Chemical Reactions on Polymers 9780841214484, 9780841212121, 0-8412-1448-4

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Chemical Reactions on Polymers

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

ACS

SYMPOSIUM

SERIES

Chemical Reactions on Polymers Judith L. Benham, EDITOR 3M Company

Jame James River Corporation

Developed from a symposium sponsored by the Division of Polymer Chemistry, Inc., and the Division of Polymeric Materials: Science and Engineering at the 192nd Meeting of the American Chemical Society, Anaheim, California, September 7-12, 1986

American Chemical Society, Washington, DC 1988

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

364

Library of Congress Cataloging-in-Publication Data Chemical reactions on polymers/editors, Judith L. Benham, James F. Kinstle. p.

cm.—(ACS symposium series; 364)

"Developed from a symposium sponsored by the Division of Polymer Chemistry, Inc., and the Division of Polymeric Materials: Science and Engineering at the 192nd Meeting of the American Chemical Society, Anaheim, California, September 7-12, 1986." Bibliographies: p. Includes indexes. ISBN 0-8412-1448-4 1. Polymers and polymerization—Congresses. 2. Chemical reactions—Congresses I. Benham, Judith L., 1947. III. American Chemical Society. Division of Polymer Chemistry, Inc. IV. American Chemical Society. Division of Polymeric Materials: Science and Engineering. V. American Chemical Society. Meeting (192nd: 1986: Anaheim, Calif.) VI. Series. QD380.C456 668.9—dc19

1988 87-31913 CIP

Copyright © 1988 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. This consent is given on the condition, however, that the copier pay the stated per copy fee through the Copyright Clearance Center, Inc., 27 Congress Street, Salem, M A 01970, for copying beyond that permitted by Sections 107 or 108 of the US. Copyright Law. This consent does not extend to copying or transmission by any means—graphic or electronic—for any other purpose, such as for general distribution, for advertising or promotional purposes, for creating a new collective work, for resale, or for information storage and retrieval systems. The copying fee for each chapter is indicated in the code at the bottom of the first page of the chapter. The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN THE UNITED STATES OF AMERICA

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

ACS Symposium Series M. Joan Comstock, Series Editor 1988 ACS Books Advisory Board Harvey W. Blanch

Vincent D. McGinniss

University of California—Berkeley

Battelle Columbus Laboratories

Malcolm H. Chisholm

Daniel M. Quinn

Indiana University

University of Iowa

Alan Elzerman Clemson University

John W. Finley Nabisco Brands, Inc.

C. M. Roland U.S. Naval Research Laboratory

Natalie Foster Lehigh University

W. D. Shults Oak Ridge National Laboratory

Marye Anne Fox The University of Texas—Austin

Roland F. Hirsch U.S. Department of Energy

G. Wayne Ivie USDA, Agricultural Research Service

Geoffrey K. Smith Rohm & Haas Co.

Douglas B. Walters National Institute of Environmental Health

Michael R. Ladisch

Wendy A. Warr

Purdue University

Imperial Chemical Industries

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Foreword The ACS S Y M P O S I U M S E R I E S was founded in 1974 to provide a

medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing A D V A N C E S IN C H E M I S T R Y SERIES except that, in order to save time, the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, lished papers are no research are acceptable, because symposia may embrace both types of presentation.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Preface C H E M I C A L R E A C T I O N S O N P O L Y M E R S has emerged as one of the most active fields in polymer science because of its unique ability to produce specialty polymers with desirable chemical and physical properties through modification of readily available polymers. The field is extremely diverse and has grown to encompass many topics. The use of chemical modification to introduce functional reactiv int polymers t alte polymer surfaces, to provid to aid in analytical characterization of polymers represents a significant portion of the scope of this scientifically interesting and technologically useful field of research. Other topics include radiation chemistry of polymers, use of dopants for improved conductive properties, and polymer modification for biological applications (e.g., drugs and peptide synthesis) and for electronic applications. The rapid growth of these areas, and the continuing identification of new opportunities for specialty polymers, has led to an increasing body of literature reporting research on polymer modification, as well as numerous review articles and monographs, during the last decade. The symposium from which this book was developed had three goals: to provide a single forum for presentation of research from several diverse areas of polymer modification by chemical reactions; to present to the scientific community the most recent and emerging technical achievements of leading academic, industrial, and government researchers in the field; and to bring together an international group of scientists, specializing in reactions on polymers, for discussion of topics in this rapidly growing and changing field of polymer science. The speakers and subjects were selected with emphasis on six active research areas in chemical reactions on polymers: reactive polymers, new synthesis routes, surface modification of polymers, specialty polymers with polar/ionic groups, chemical modification for analytical characterization, and chemical modification for functionalization and curing. Inclusion of all facets of research within each of the areas was not possible; however, a good balance of topics that had not been covered previously in other symposia or books was sought. The field of chemical reactions on polymers is so diverse that one book cannot completely cover this continually expanding area of polymer science. Instead, the chapters of this book provide current research results and balanced coverage of six areas of the field. The book is designed to be

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In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

useful to chemists working with polymers in a variety of application areas, particularly to researchers who are seeking convenient routes for modifica­ tion of polymers, and to chemists interested in the synthesis and use of polymeric reagents and catalysts. The conclusions presented in this book are those of the authors, whom 1 thank for their participation in the symposium and for their preparation of manuscripts for publication in this book. I also thank Rebecca C. Nelson for her administrative assistance in preparation of the symposium and this book. Acknowledgment is made to the donors of The Petroleum Research Fund, administered by the American Chemical Society, for partial support of the symposium. Acknowledgment for financial contributions to the symposium is made to the following companies: Amoco Corporation; A R C O Chemical Company; Ε. I. du Pont de Nemours and Company; Eastman Kodak Company General Electri Company Owens-Cornin Fiberglas Corporation; Pfize tion; P P G Industries, Inc.; The Procter & Gamble Company; Signal Research Center, Inc.; and Texaco, Inc. JUDITH L . BENHAM

3M Specialty Chemicals Division St. Paul, MN 55144 September 22, 1987

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In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 1

Modification of Condensation Polymers Challenges and Opportunities William H . Daly, Soo Lee, and C. Rungaroonthaikul Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803

Electrophilic elaboration including bromination, nitration, chloromethylation, and aminomethylation of poly(2,6-dimethyl-1,4-phenylene oxide) poly -(arylene ether sulfone lene arylene ether which minimize degradation of the polymer substrates are defined with the aid of 2,2-bis[4'-(4"-phenyl­ -sulfonyl phenoxyl) phenyl]propane, a model for poly (arylene ether sulfone). Further modifications of the functionalized polymers include; reduction of the nitro or cyano substituents to amine or aminomethyl groups, respectively, quaternization of the chloromethyl group, and application of the Gabriel synthesis to the introduction of aminomethyl groups. Applications of the amino- and aminomethyl polymers as substrates for the grafting of γ-benzyl-L-glutamate N-carboxyanhydride to poly(arylene ether sulfone) are reported. Graft copolymers soluble in pyridine, DMSO and halogenated solvents are described. In recent years, especially following Merrifield's revolutionary invention of s o l i d phase synthesis , there has been a steadily increasing interest i n the a p p l i c a b i l i t y of polymers as participants i n chemical reactions. High levels of a c t i v i t y are apparent i n the f i e l d s of polymer-bound catalysts, polymeric reagents, inert c a r r i e r s for reactive substrates, and polymeric protective groups. The rapid growth i n this area i s evident from the many review a r t i c l e s and monographs published during the past decade. Reactive polymers can be synthesized by either polymerizing or copolymerizing monomers containing the desired functional groups, or performing one or more modifications on a suitable polymer to introduce the essential f u n c t i o n a l i t y . Polymers produced d i r e c t l y by polymerization of functionalized monomers have well defined structures, but the physical and mechanical properties of the 1

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0097-6156/88/0364-0004$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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resultant materials are not always suitable for the applications i n mind. Since the purpose for immobilizing the reagent/catalyst i s to optimize the environment for the active s i t e , a procedure leading to better defined polymer characteristics i s more desirable. Tailored polymeric systems can be produced by modifying preformed polymers such as; polystyrene, polyamides, poly(oxy-2,6-dimethyl-l,4phenylene), phenoxy resins and poly(arylene ether sulfone). * The support most commonly employed, polystyrene, f u l f i l l s the major c r i t e r i a favoring chemical modification, i . e . s u f f i c i e n t chemical s t a b i l i t y to allow essential transformations without degrading the backbone, compatibility with organic solvents, and active sites (aromatic rings), which can be functionalized by either e l e c t r o p h i l i c substitution or metalation followed by treatment with nucleophiles. Interestingly, only limited work on the changes i n the chain extension and f l e x i b i l i t y produced by modifying polystyrene resins has been reported. Although polystyren i glas t temperature (Tg=105°), solven extremely f l e x i b l e and "immobilize" a reagent. The resultant crosslinked resins i n h i b i t the transport of reactants and products to the active sites within the dense polymer matrix. Immobilization of reagents on polymers with r e l a t i v e l y r i g i d chains should r e s t r i c t segmental motion without i n h i b i t i n g d i f f u s i o n . L i t t l e data on the influence of r e s t r i c t e d chain mobility on the efficacy of a polymer support i n enhancing catalyst and/or reagent properties has been reported, so we have focused our attention in this area. Our interest i n semipermeable and reactive membranes has lead to a detailed study of the chemical modification of condensation polymers. The excellent mechanical properties exhibited by the modified polymers suggest that they could be employed i n s p e c i a l i t y applications such as; permselective membranes, conducting films, and catalyst membranes. 1

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E l e c t r o p h i l i c Modification of Condensation

Polymers.

In contrast to the activating influence of the hydrocarbon backbone attached to aromatic substituents i n polystyrene derivatives, the linking units of condensation polymers exhibit varying influences on the r e a c t i v i t y of enchained aromatic backbones. Linking units which promote e l e c t r o p h i l i c substitution tend to make the corresponding condensation polymers more reactive than polystyrene. The inductively activated aryloxy groups present i n the backbone of poly(arylene ether sulfone), _1, poly(2,6-dimethyl-l,4-phenylene oxide), 2j poly(2,6-diphenyl-l,4-phenylene oxide), _3, and phenoxy resin, make them excellent substrates for e l e c t r o p h i l i c modification at the sites designated i n the structures on the next page. Unfortunately, some of the more common commercially available condensation polymers are based upon linking units which deactivate aromatic rings; thus, polyamides, polyesters, and polycarbonates can be modified with e l e c t r o p h i l i c reagents only under conditions which lead to cleavage of the backbone linkages.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

β

S

™3

Halogenation. Poly(2,6-dimethyl- and 2,6-dipheny1-1,4-phenylene ether) can be aryl-brominated simply by exposure to a bromine solution; no catalyst i s r e q u i r e d . In fact, the use of Lewis acid catalysts to promote the chlorination of poly(2,6-dimethy1-1,4phenylene ether) leads to substantial degradation of the molecular weight of the chlorinated products. Membranes produced from ring brominated PPO (40% wt Br) exhibited enhanced permeability to CHi+ and CO2 and proved to be more selective i n separating CHi+/C02 mixtures. The a r y l bromides undergo f a c i l e metalation with butyl lithium to produce a r y l l i t h i u m derivatives with the expected organometallic activity. For example, reaction of l i t h i a t e d PPO with carbon dioxide produces a carboxylated PPO which exhibits unique blending characteristics . In general, i f condensation polymers are prepared with methylated a r y l repeat units, free r a d i c a l halogenation can be used to introduce halomethyl active sites and the limitations of e l e c t r o p h i l i c aromatic substitution can be avoided. The halogenation technique recently described by F o r d , involving the use of a mixture of hypohalite and phase transfer catalyst to chlorinate poly(vinyl toluene) can be applied to suitably substituted condensation polymers. 6

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Sulfonation. In a c l a s s i c paper, Noshay and Robeson detailed the conditions for sulfonating poly(arylene ether sulfone) using a sulfur t r i o x i d e - t r i e t h y l phosphate complex as the sulfonating agent. Chlorosulfonic acid can be used to sulfonate PPO. The inherent i n s t a b i l i t y of the sulfonated PP0 could be improved by converting the sulfonate group to a stable sulfone group. Treatment of PPO with a r y l s u l f o n y l chloride under Friedel-Crafts conditions produced a series of arylsulfone modified PPO's, which exhibited improved gas permeation c h a r a c t e r i s t i c s . Since the sulfonated 13

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polymers make excellent membranes for reverse osmosis applications, the l i t e r a t u r e i s rather extensive and a complete review i s beyond the scope of this paper. Reactivity of Modified Condensation Polymers 1 6

Verdet and S t i l l e employed brominated poly(phenylene oxide) intermediates i n an e f f o r t to synthesize more stable catalyst supports containing (cyclopentadienyl)metal complexes. Treatment of poly(oxy-2,6-dimethyl-l,4-phenylene) with N-bromosuccinimide under photolytic conditions produced only the bromomethyl derivative i f the D.F. did not exceed 0.35. Subsequent treatment of the bromomethylated polymer with sodium cyclopentadienide afforded the cyclopentadienyl functionalized polymer, J^, but the reaction was accompanied by crosslinking and i t was not possible to remove the bromomethyl substituents quantitatively. An alternative synthesi f thermall stabl cyclopentadienyl functionalized polymer diphenyl-l,4-phenylene) to produce an a r y l l i t h i u m polymer. Arylation of 2-norbornen-7-one with the metalated polymer yielded the corresponding 2-norbornen-7o l derivative. Conversion of the 7-ol to 7-chloro followed by treatment with butyl lithium generated the benzyl anion which undergoes a retro Diels-Alder reaction with the evolution of ethylene to produce the desired a r y l cyclopentadiene polymer, ^ . The polymer was soluble i n a variety of solvents indicating that no crosslinking occurred during functionalization-

The polymers were converted to supported catalysts corresponding to homogeneous complexes of cobalt, rhodium and titanium. The cobalt catalyst exhibited no r e a c t i v i t y i n a FischerTropsch reaction, but was effective i n promoting hydroformylation, as was a rhodium analog. A polymer bound titanocene catalyst maintained as much as a 40-fold a c t i v i t y over homogeneous titanocene i n hydrogénations. The enhanced a c t i v i t y indicated better s i t e i s o l a t i o n even without crosslinking. Even i n solution the relative r i g i d i t y of the polymer support can play a s i g n i f i c a n t role i n the r e a c t i v i t y of attached functional groups. Contrasting studies conducted with chloromethylated derivatives of poly(arylene ether sulfone) (Tg- 175°C), phenoxy resin (Tg= 65°C) and polystyrene (Tg= 105°C) allow evaluation of chain r i g i d i t y e f f e c t s . We have shown that the rates of quaternization of chloromethylated poly(arylene ether sulfones) and phenoxy resin deviate from the anticipated second order process at

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

high degrees of conversion; normal kinetics are observed when chloromethylated polystyrene and low molecular weight sulfone model compounds are used as the s u b s t r a t e s . Variations i n the structure of the t e r t i a r y amines used as nucleophiles i n this k i n e t i c study changed the i n i t i a l rates of quaternization, but did not alter the tendency for deviation from second order k i n e t i c s . In each case, the process appeared to be second order u n t i l the extent of substitution reached 40-50%, beyond that point the rate begins to decrease. The phenomena are not influenced by the addition of e l e c t r o l y t e s . Viscosity measurements during the reaction reveal a steady increase i n the r e l a t i v e v i s c o s i t y u n t i l the breakpoint i s reached and then, the r e l a t i v e v i s c o s i t y remains constant for the remainder of the reaction. Addition of electrolytes surpresses the chain expansion as the extent of charge along the backbone increases. The chloromethyl derivatives of _1 and _2 can be converted to the corresponding phosphonium salts by treatment with triphenyl phosphine. A subsequen of these salts with formaldehyd The v i n y l substituents could be converted by bromination and dehydrobromination to pendant ethynyl groups. Our objective i n this paper i s to i l l u s t r a t e the methods for functionalizing poly(arylene ether sulfone). Particular attention w i l l be paid to bromination, n i t r a t i o n , amination, chloromethylation, and aminomethylation of _1 and i t s corresponding model compound. 17

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EXPERIMENTAL Melting points, measured i n open c a p i l l a r y tubes using a ThomasHoover melting point apparatus, are uncorrected. Elemental analyses were performed by Galbraith Laboratories, Knoxville, Tennesee. B. and C-NMR spectra were generally obtained with an IBM AF-100, i f necessary the higher f i e l d Bruker WP-200 or AM-400 NMR spectrometer were employed. Chemical s h i f t s are given i n parts per m i l l i o n (ppm) on a σ scale downfield from tetramethylsilane (TMS). Infrared spectra were recorded with a Perkin-Elmer 283 spectrophotometer. Low molecular weight solids were dispersed i n KBr p e l l e t s ; polymer films were cast from CHC13. I n t r i n s i c v i s c o s i t i e s were measured by standard procedures using a Cannon Ubbelohde d i l u t i o n viscometer. A l l solvents used for general applications were of reagent grade. For special purposes, p u r i f i c a t i o n of solvents was effected using standard procedures. A l l other reagents were used as supplied commercially except as noted. A solution of chloromethyl methyl ether (6 mmole/mL) i n methyl acetate was prepared by adding acetyl chloride (141.2 g, 1.96 mol) to a mixture of dimethoxy methane (180 mL, 2.02 mol) and anhydrous methanol (5.0 mL, 0.12 m o l ) . The solution was diluted with 300 mL of 1,1,2,2-tetrachloroethane and used as a stock solution for the chloromethylation experiments. Poly[oxy-1,4-phenylene-(1·-methylethylidene)-l ,4 -phenylene-oxy(2"-cyano)-l",3"-phenylene], 20, was prepared from bisphenol-A and 2,6-dichlorobenzonitrile according to the precedure of McGrath et al. l

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In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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Modification of Condensation Polymers

DALY ET AL.

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Preparation of 2,2-bis[4 -(4"-phenylsulfonylphenoxyl)phenyl] propane,7. Treatment of the disodium s a l t of bisphenol-A (20 g. 0.088mol) with chlorophenyl phenyl sulfone (44.3 g, 0.175 mol) i n a 2:1 v:v toluene:DMS0 (100 mL) according the procedure of Johnson et al. afforded 51.2 g of crude adduct. R e c r y s t a l l i z a t i o n from benzene yielded the pure _7, mp 182-83° C; mol wt.(mass spec) 660.1. H NMR (CDC13): 1.7 (s, 6H, 2-CH3); 6.7-7.0 (m, 16 H, aromatic H s ) ; 7.8-7.95 (m, 8H, aromatic H s ortho to SO2). C NMR (CDCI3): 30.5 (-CH3); 42.2 (CH3-C-CH3); 117.7, 119.6, 127.2, 128.3, 129.1. 129.7, 132.8, 135.0, 142.0, 147.0, 152.7, 161.9 (aromatic C's). Analysis:Calc d for C39H32O6S2: C, 70.91; H, 4.84; 0, 14.53; S, 9.72. Found: C, 70.83; H, 4.99, 0, 14.54; S, 9.66. 2 2

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Bromination of 2,2-bis[4 -(4"-phenylsulfonylphenoxyl)phenyl]propane. A solution of 3.0 g (4.70 mmol) of ]_ i n 25 mL of CHCI3 was s t i r r e d in the dark under Ar at room temperature while a solution of 7.51 g (47.0 mmol) of Br2 i n 20 mL of CHCI3 was added After 5 h of s t i r r i n g , the excess bromin min. The solvent was evaporate residue was washed with 100 mL of methanol. After drying in vacuo at 45° for 12 h, 2.95 g (78.9%) of 2,2-bis-[3-bromo-4-(4-phenylsulfonylphenoxy)phenyl]propane, mp 87-91°C was obtained. *H NMR (CDCI3): 1.68 (s, 6H, 2-CH3);6.93-7.54 (m, 16 H, aromatic H's); 7.86-7.98 (m, 8H, aromatic H s ortho to SO2). C NMR (CDCI3): 30.6 (-CH3);42.5 (CH3-C-CH3); 115.6, 117.0, 121.9, 127.3, 127.5, 129.1, 129.9, 132.0, 132.9, 135_.4, 141.9, 148.5, 149.6, 161.1 (aromatic C s); IR ( f i l m ) , 1050 cm (-Br). f

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N i t r a t i o n of 2,2-bis[4 -(4"-phenylsulfonylphenoxyl)phenyl]propane. The process reported by C r i v e l l o was u t i l i z e d as follows: a solution of 3.30 g (5.2 mmol) of ]_ i n 50 mL of CHCI3 was blended with 0.84 g (10.4 mmol) of ammonium nitrate and 5.88 mL (41.6 mmol) of t r i f l u o r o a c e t i c anhydride (TFAA) i n a 100 mL RBF. The mixture was s t i r r e d at room temperature for 11 h. After evaporating the excess TFAA by purging with argon for 30 min, the solution volume was reduced to 5 mL. The product was precipitated by pouring the reaction mixture into 100 mL of methanol, recovered by f i l t r a t i o n , washed with 50 mL of water and dried in vacuo at 35° for 48 h; 3.85 g (75.3%) of 2,2-bis[3-nitro-4-(4-phenylsulfonyl-phenoxyl)phenyl] propane, % mp 104-6° was obtained. H NMR (CDCI3): 1.74 (s, 6H, 2CH3); 7.19, 7.31, 7.60, 7.68, 8.04 (m, 24 H, aromatic H's); C NMR (CDC13): 30.5 (-CH3); 42.7 (CH3-C-CH3); 117.9, 120.1, 122.9, 124.0, 127.4, 128.3, 129.2, 130.0, 133.1, 136.6, 141.6 146.4, 146.7, 160.4, (aromatic C's); IR ( f i l m ) ; 1535, 1340 cm (-NO2). Z : i

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Reduction of 2,2-bis[3 -nitro-4 -(4"-phenylsulfonylphenoxyl)phenyl] propane. Compound J3, 200 mg (0.55 meg) was dissolved i n a mixture of 30 mL of dichloromethane (DCM) and 30 mL of methanol and 240 mg of 10% palladium on charcoal was added. After purging the solution with argon for 30 min, 520 mg (13.6 mmol) of sodium borohydride was added portionwise over 10 min. The reaction mixture was s t i r r e d under argon for 1 hr before addition of 30 mL of DCM. The mixture was f i l t e r e d , the f i l t r a t e evaporated, and the residue extracted with DCM. Evaporation of the extract yielded 140 mg (76.2%) of 2,2-

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

10 1

bis[3'-amino-4 -(4"-phenylsulfonylphenoxyl)phenyl]propane, _10, mp 85-9°. H NMR (CDCI3): 1.76 (s, 6H, 2-CH3); 7.02, 7.11, 7.31, 7.46, 7.52, 7.88, 7.95, 7.98 (m, 24 H, aromatic H's); C NMR (CDCI3): 30.8 (-CH3); 42.4 (CH3-Ç-CH3); 115.6, 116.6, 117.4, 120.6, 127.4. 129.2, 129.9, 132.9, 134.8, 138.2, 139.1, 142.1 148.8,161.8 (aromatic C's); IR ( f i l m ) : 3460, 3380, 1625 cm"" (-NH2). X

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Chlorornethylation of 2,2-bis[4'-(4"-phenylsulfonylphenoxyl)pheny1] propane. A solution of J_> 40 g (0.06 mol) was blended with 400 mL of 6 M chloromethyl methyl ether solution and 0.7 mL (6 mmol) of SnCli+ i n a 500 mL resin k e t t l e , and the mixture was refluxed for 8 h under argon. The solvent was d i s t i l l e d u n t i l the volume was reduced to 20 mL and 300 mL of ethanol was added to produce a clear solution. The product, 2,2-bis[3-chloromethyl-4-(4-phenylsulfonylphenoxyl) phenyl]propane, _11, c r y s t a l l i z e d from the i c e cooled solution, 40.2 g (87%) mp 182-83°C was isolated by f i l t r a t i o n . H NMR (CDCI3): 1.7 (s 6H 2-CH3) C1) 6.7-7.0 (m, 16 H, aromatic H's) SO2). C NMR (CDC13): CH3); 117.7, 119.9, 127.3, 128.7, 129.1, 129.3, 129.8, 132.8, 135.5, 142.1, 147.2, 150.9, 161.5 (aromatic C s ) . Analysis: C a l c d for C1+1H31+06S2C12: C, 64.98; H, 4.5; CI, 9.36; S, 8.56; 0, 12.66. Found: C, 64.86; H, 4.69; CI, 9.47, S, 8.62; 0, 12.30. l

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Phthalimidomethylation of 2,2-bis[3'-chloromethyl-4'-(4"-phenylsulfonylphenoxyl)phenyl]propane, 11. To a solution of 1.0 g (2.64 meq) of i n 20 mL DMF was added 1.20 g (6.49 mmol) of potassium phthalimide. After s t i r r i n g for 8 h at 100° C, the unreacted potassium phthalimide was removed by f i l t r a t i o n and the f i l t r a t e evaporated under reduced pressure. The residue was washed sequentially with 30 mL of d i s t i l l e d water and 15 mL of methanol. After drying i vacuo at 40° C for 24 h, 1.16 g (90.1%) of the product, 2,2-bis[3-phthalimidomethy1-4'-(4"-phenylsulfonylphenoxyl)phenyl]propane, JL2^ was obtained. Spectral data were consistent with quantitative substitution: H NMR (CDCI3): 1.69 (s, 6H, 2-CH3); 4.76 (s, 4H, -CH2N Phth); 6.8-7.5 (m, 16 H, aromatic H s ) ; 7.61, 7.64 (d, 8H, aromatic H's i n phthalimide); 7.8-7.84 (m, 8H, aromatic H's ortho to SO2). C NMR (CDCI3): 30.5 (-CH3); 37.2 (-CH2NPhth); 42.2 (CH3-C-CH3); 116.9, 117.1, 119.5, 120.4, 123.0, 127.4, 127.6, 127.8, 129.1, 129.7, 131.7, 132.9, 133.9, 134.9, 141.5, 147.4, 150.3, 161.8, 167.5 (aromatic C's); IR ( f i l m ) ; 1772, 1716 cm" (phthalimide C O ) . n

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f

13

1

Hydrazinolysis of 2,2-bis[3'-phthalimidomethyl-4'-(4"-phenylsulfonyl phenoxyl)phenyl]propane, 12. A solution of 1.00 g (2.0 meq) of 12 and 3 mL (34.5 mmol) of hydrazine hydrate i n 25 mL of methanol was heated at reflux for 24 h. After evaporation of solvent, the residue was extracted with 30 mL of CHCI3, the extract was evaporated, and the crude product was washed sequentially with 25 mL of 2% aqueous sodium bicarbonate, 100 mL of water, and 50 mL of methanol. Drying in vacuo at 40° C for 24 h afforded 0.70 g (97.5%) of 2,2-bis[3-aminomethyl-4'-(4"-phenylsulfonylphenoxyl)phenyl]propane, U NMR (CDCI3): 1.69 (s, 6H, 2-CH3); 2.07 l

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

1.

DALY ETAL.

11

Modification of Condensation Polymers

(b,-NH2); 3.73 (s, 4H, -CH^N^; 6.79-7.54 (m, 16 H, aromatic H's); 7.84, 7.95 (d, 8H, aromatic H's ortho to S02). C NMR (CDCI3): 30.9 (-CH3); 41.7 (-CH2NH2); 42.6 (CH3-C-CH3); 117.1, 120.2, 127.0, 127.4, 127.8, 129.2, 129.6, 130.0, 133.0, 134.4, 135.1, 142.0 147.8, 150.4, 162.0, (aromatic C's); IR ( f i l m ) ; 3390, 3340 cm (-NH2). 13

±

1

Bromination of Poly(arylene ether sulfone). A solution of 4.42 g (10.0 meq) of i n 50 mL of CHCI3 was s t i r r e d i n the dark under Ar at room temperature while a solution of 3.55 g (22.2 meq) of Br2 i n 20 mL of CHCI3 was added. After 17 h of s t i r r i n g , the excess bromine was removed by purging with Ar for 30 min. The solution volume was reduced to 40 mL before pouring into 700 mL of methanol. The precipitated product was recovered by f i l t r a t i o n , washed with 100 mL of methanol, and dried in vacuo at 45° overnight. A t o t a l of 4.86g of brominated polymer, 14, was recovered. H NMR (CDCI3) 1.68 (s 6H 2-CH3) 6.93-7.54 (m 11 H aromatic H's); 7.86-7.9 C NMR (CDC13): 30.6 (-CH3);42. 119.9, 121.9, 127.6, 128.4, 129.8, 131.4, 135.5, 146.3 148.6, 150.2, 153.2, 161.1 (aromatic C's); IR ( f i l m ) ; 1050 cm (-Br). X

13

L

1

Nitration of Poly(arylene ether sulfone). A solution of 4.00 g (0.05 mol) of ammonium nitrate i n 42 mL (0.3 mol) of t r i f l u o r o a c e t i c anhydride was added to 22.10 g (0.05 eq) of _1 dissolved i n 200 mL of CHC13· The slurry was s t i r r e d at room temperature for 24 h during which time the inorganic s a l t dissolved. The volume of the reaction mixture was reduced to 100 mL under reduced pressure before precipitating the product by pouring the reaction mixture into 1 L of methanol. The product was separated by f i l t r a t i o n and washed sequentially with 200 mL methanol, 100 mL saturated aqueous NaHC03, 400 mL of water, and 100 mL of methanol. After drying in vacuo for 24 h at 45° C, 22.10 g (99.2%) of poly(nitroarylene ether sulfone),15, D.F.= 1.0, [η] - 0.34 dl/g (CHCI3 at 30° C) was obtained. R NMR (CDCI3): 1.73 (s, 6H, 2-CH3); 6.89-7.40, 7.50, 7.8-7.9 (m, 15 H, aromatic H's); C NMR (CDCI3): 30.6 (-CH3); 42.7 (CH3-C-CH3); 117.5, 117.9, 119.8, 123.9, 128.4, 129.9, 135.4, 136.9, 141.8, 145.4, 145.9, 146.9, 148.8, 153.5, 160.8, 161.9, (aromatic C's); IR ( f i l m ) ; 1550, 1360 cm (-NO2). l

13

1

Reduction of Nitrated Poly(arylene ether sulfone), 15. A 250 mL round bottomed flask was charged with 3.00 g (6.16 meq) of 15, D.F.= 1.0, and 30 mL of THF, 0.01 g of tetrabutylammonium chloride, and 5.00 g (22.1 mmol) of stannous chloride. After s t i r r i n g for 30 min at room temperature, 100 mL of cone. HC1 was added over a 30 min i n t e r v a l and s t i r r i n g was continued for 48 h at 70° C. The THF was evaporated and the residue was neutralized with s o l i d NaOH i n an ice bath. The poly(aminoarylene ether sulfone), 16, was extracted from the residue with 50 mL CHCI3, reprecipitated by adding the CHCI3 solution to 500 mL of methanol, and dried in vacuo at 50° C for 16 h. The product, 1.20 g (42.6%), [η]- 0.32 dl/g (CHCI3 at 30° C) exhibited the following spectra: H NMR (CDCI3): 1.64 (s, 6H, 2CH3); 3.69 (b, 2H, -NH2); 6.50-7.29, (m, 11 H, aromatic H's); 7.78, 7.86 (d, 4H, aromatic H's ortho to SO2); C NMR (CDC13): 30.8 X

13

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

12

CHEMICAL REACTIONS

O N

POLYMERS

( - C H 3 ) ; 42.4 ( C H 3 - C - C H 3 ) ; 115.6, 116.6, 117.4, 117.7, 119.7, 120.7, 128.4, 129.7, 135.4, 138.3, 139.1, 147.3, 148.6, 152.8, 161.7, 161.9, (aromatic C s ) ; IR ( f i l m ) ; 1620, 3360, 3480 cm (-NH2). f

1

Chloromethylation of Poly(arylene ether sulfone). To a 500 mL three-necked resin k e t t l e equipped with condenser, mechanical s t i r r e r , and pressure equalizing dropping funnel, was charged with 75 mL of chloromethyl methyl ether solution and 0.13 mL (1.13 mmol) of SnCli+. After the solution was heated to 1 0 0 ° C, a solution of _1 ( 5 . 0 g, 11.25 meq) i n 63 mL of tetrachloroethane was added slowly over a period of 15 min. The reaction mixure was s t i r r e d and maintained at 100° C for 3 hours before the catalyst was deactivated by i n j e c t i n g 2 . 0 mL of methanol. The reaction volume was reduced to 70 mL before p r e c i p i t a t i n g the chloromethylated polymer i n methanol. The polymer was recovered by f i l t r a t i o n , washed with methanol and dried i n a vacuum dessicator for 24 h. The crude polymer was p u r i f i e d b dissolutio i dioxane reprecipitatio i methanol, followed by successiv 40% aqueous dioxane containin After drying in vacuo at 50° C for 48 h, 5.81 g (96.7%) of, Γ 7 , was recovered. H NMR ( C D C I 3 ) : 1 . 6 8 (s, 6 H , 2 - C H 3 ) : 4.53 (s, 4 H , - C H 2 C I ) ; 6 . 8 - 7 . 4 (m, 10 H, aromatic H's); 7 . 9 (d, 4 H , aromatic H's ortho to S 0 2 ) . C NMR ( C D C I 3 ) : 30.7 ( - C H 3 ) ; 40.8 ( - C H 2 C I ) ; 42.4 ( C H 3 - C - C H 3 ) ; 117.8, 1 2 0 . 1 , 128.9, 129.1, 129.5, 129.8, 135.9, 147.4, 151.1, 162.0 (aromatic C's). Elemental Analysis was consistent with the introduction of 1.89 - C H 2 C I groups/repeat u n i t . Anal. Found: C, 6 4 . 9 7 ; H, 4.72; CI, 12.55; S, 6 . 2 0 ; 0 . 11.91. X

1 3

Phthalimidomethylation of Poly(arylene ether sulfone). E l e c t r o p h i l i c Approach. To a mechanically s t i r r e d solution of 22.10 g (0.05 eq) of _1 i n 200 mL of DCM was added dropwise a solution of 8.85 g (0.05 mol) of N-hydroxymethylphthalimide and 5 . 0 g of trichloromethanesulfonic acid i n 200 mL of t r i f l u o r o a c e t i c acid. The addition required 1 h during which time the mixture darkened to a deep brown. After s t i r r i n g for 6 h at room temperature, the polymer was precipitated i n 1 . 5 L of methanol and washed sequentially with 400 mL of cone, ammonium hydroxide, 1 . 5 L of water, and 1 . 5 L of methanol. The poly(phthalimidomethylarylene ether sulfone),_18^, D.F.= 0 . 5 , was isolated as a white powder, 19.90 g (76.3%), [η]= 0.40 dl/g ( C H C I 3 at 30° C). Nucleophilic Approach. To a mechanically s t i r r e d solution of 5 . 0 0 g (18.5 meq) of J J , D. F.= 2 . 0 , i n 50 mL of DMF was added a solution of 6 . 0 0 g (26.9 meq) of potassium phthalimide i n 150 mL of DMF. After s t i r r i n g for 10 h at 1 0 0 ° C, the precipitated salts were removed by f i l t r a t i o n , and the product was isolated by pouring the f i l t r a t e into 1 L of methanol. Following a water wash and a methanol wash, the precipitate was dried at 4 5 ° C for 24 h; 5.50 g, ( 9 9 . 1 % ) of the product, J L 8 , D. F.= 2 . 0 , [η] = 0.41 dl/g, was obtained. Spectral data were consistent with quantitative substitution. The spectra obtained from samples prepared by either technique exhibited the following q u a l i t a t i v e absorbances: H NMR ( C D C 1 3 ) '· 1.69 (s, 6 H , 2 - C H 3 ) ; 4.76 (s, 4 H , - C H 2 N P h t h ) ; 6 . 8 - 7 . 4 (m, 10 H, aromatic H's); 7 . 6 6 (d, 8 H , aromatic H's i n phthalimide); 7.7-7.9 (m, 4 H , aromatic H's ortho to S 0 2 ) . X

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

1.

DALY ET AL.

Modification

13

of Condensation Polymers

13

C NMR (CDCI3): 30.9 (-CH3); 38.1 (-CH NPhth); 42.4 (CH3-C-CH3); 117.1, 120.1, 127.5, 127.6, 129.6, 135.4, 147.5, 150.3, 161.9, (aromatic C's); IR ( f i l m ) ; 1773, 1717 cm" (phthalimide C=0). 2

1

Hydrazinolysis of Poly(phthalidimidomethylarylene ether sulfone). To a solution of 5.00 g (4.94 meq) of JL8, D.F.= 0.5, i n 150 mL of THF and 150 mL of ethanol, was added 3.5 mL (51.6 mmol) of hydrazine hydrate at 70° C. After s t i r r i n g for 18 h at 70° C, the precipitate was recovered by f i l t r a t i o n , and extracted with 300 mL of THF. The f i l t r a t e was evaporated and the residue extracted with 50 mL of THF. The extracts were combined, the volume reduced to 50 mL, and the product precipitated by pouring the solution into 500 mL of methanol. The polymer was washed sequentially with 50 mL of saturated aqueous NaHC03, 200 mL of water, and 200 mL of methanol, dried in vacuo at 50° C for 16 h, and 3.50 g (79.9%) of poly(aminomethylarylene ether sulfone),19, D.F.= 0.5, [η]= 0.39 dl/g, was recovered. R NMR (CDCI3): 1.69 (s 6H 2-CH3); 1.92 (b,lH, -NH2); 3.73 (s H's); 7.80-7.89 (d, 4H (CDCI3): 30.9 (-CH3), 41.8 (-CH2NH2); 42.5 (CH3-C-CH3); 117.0, 117.7, 119.8, 120.2, 125.7, 128.4, 129.7, 133.4, 147.1, 147.7, 149.9, 152.9, 161.9, (aromatic C's), IR ( f i l m ) , 3400 cm" (-NH2). l

1

Reduction of Poly(2-cyano-l,3-phenylene arylene ether), 20 Twenty-five mL of a 1.0 M solution of lithium aluminum hydride (LAH) i n THF was cooled to 0° C before adding a solution of 1.64 g (5.0 meg) of ^0 i n 120 mL of THF. The resultant slurry was s t i r r e d for 24 h at 0° C, refluxed for 1 h, recooled to 5° C, and the excess LAH decomposed with 2 mL of water. The volume of the solution was reduced to 25 mL before pouring the mixture into 500 mL of 5% HC1 to dissociate the amine aluminum salt complex and precipitate the polymer. The polymer was recovered by f i l t r a t i o n , r e s l u r r i e d i n 20 mL of water and the pH adjusted to 9.0 with NaOH. After recovery of the neutralized polymer was recovered, i t was dried in vacuo redissolved i n CHCI3, and reprecipitated using water as the nonsolvent. F i n a l drying in vacuo for 24 h at 35° C l e f t 1.2 g (72.3%) of poly[oxy-1,4-phenylene-(1-methylethylidene)-l',4'-phenylene-oxy(2"-aminomethyl)-l ,3"-phenylene], 21, [η] (CHC13) - 0.3 d l / g . H NMR (CDC1 3): 1.67-1.85 (b, 8H, 2 CH3 and NH2) ; 3.91 (s, 2H, -CH2-N); 6.66-7.23 (m, 11H, aromatic H's). C NMR (CDCI3): 30.95 (-CH3); 35.47 (-CH2-NH2); 42.02 (CH3-C-CH3); 114.0, 117.7, 128.0, 145.4, 155.2, 157.0 (aromatic C's). Analysis: Calc'd for C22H21NO2: C, 79.73; H, 6.39; 0, 9.65; N, 4.23. Found: C, 79.33; H, 6.42; 0, 9.9; N, 4.07. ,,

X

13

RESULTS AND

DISCUSSION

Since poly(oxy-2,6-dimethyl-l,4-phenylene) has exhibited a high tendency to undergo cleavage, rearrangements and to crosslink i n the presence of e l e c t r o p h i l i c reagents, our attention has been focused on modification of poly(arylene ether sulfone),_l, and phenoxy resin,4_. The active sites i n these polymers are the 3-positions of the bisphenol-A repeating units. We w i l l report the extent of 2i+

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

14

CHEMICAL REACTIONS ON POLYMERS

substitution by a given reagent as the degree of functionalization (D.F.) Normally only one substituent i s introduced per activated aromatic ring, i . e . , the two active rings per repeating unit i n polymers prepared from bisphenol-A lead to a maximum D.F. of 2. Selection of appropriate conditions to modify polymers i s f a c i l i t a t e d by preliminary studies with well designed model compounds. The work with model systems i s c r i t i c a l when studying condensation polymers because the main chain linkages have proved to be remarkably l a b i l e under certain conditions. Condensation of 4chlorophenyl phenyl sulfone with the disodium salt of bisphenol-A yields 2,2-bis[4 -(4"-phenylsulfonylphenoxyl)phenyl] propane, Tj excellent model for the poly(arylene ether sulfone) substrate. Conditions for quantitative bromination, n i t r a t i o n , chloromethylation, and aminomethylation of the model compound were established. Comparable conditions were employed to modify the corresponding polymers. The NMR and infrared spectra of the derivatized model compounds are useful i n establishin modified polymers. Carefu spectra for each of structures 7-13 confirms the r e g i o s e l e c t i v i t y of the substitution on the oxyphenyl unit and inertness of the phenyl sulfone units. The chemical s h i f t s of the key carbons for the analysis, those of the oxyphenyl rings, are summarized i n Table I. ,

a

Table I.

λ5

Ζ

C h a r a c t e r i z a t i o n of Model Compounds.

5

CH^

£ η

Chemical S h i f t in ppm

c

Compound

X=

7

Η

8

Br

9

N0

1

c

Obs. Cole.

2

c

Obs. Cole.

147.0

147.0

128.3

128.3

3

c

Obs. Cale.

119.6 119.6

4 Obs. Calc.

152.7

152.7

148.5

149.2

132.0

131.6

115.6

114.2

149.6

156.0

2

146.7

147.8

124.0

123.0

133.1

139.2

146.4

147.4

2

10

NH

148 8

148.3

115.6

115.9

138.2

138.8

139.1

140.3

11

CH C1

147.2

147.2

129.1

128.3

129.3

128.7

150.7

152.7

12

CH NPh

147 4

147.1

129.1

128.4

127.6

127.5

150.3

151.1

13

CH NH

147.8

146.8

127.8

126.7

135.1

134.5

150.4

151.1

2

2

2

2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

n

1.

DALY ET AL.

Modification

15

of Condensation Polymers

The calculated chemical s h i f t s are based upon a d d i t i v i t y factors f o r the sulfone, isopropylidene, and oxyphenyl linkages derived from the spectrum of The spectra of derivatives with D.F.=2 establish the chemical s h i f t s of the 3-substituted rings. Studies on model compounds with D.F.=1 confirm that the spectra of p a r t i a l l y substituted samples can be calculated by appropriate combination of the spectra of unsubstituted and 3-substituted rings. Quantitative substitution i s d i f f i c u l t to achieve with polymeric substrates, but interpretation of spectra of low D.F. derivatives i s straight forward.

24

Bromination I n i t i a l studies on bromination of poly(arylene ether sulfone) were directed toward perbromination to produce f i r e r e t a r d a n t s . The conditions used, bromine i n the presence of iron catalyst i n a l k y l bromides at reflux, must have produced substantially degraded products but approximately 6 Br/repeat unit were introduced. We wished to effect bromination under more controlled conditions to produce a range of brominated products to serve as substrates for Heck-type vinylation reactions. We found that aromatic bromination must be conducted at room temperature or below i n the presence of a large excess of bromine to assure minimal chain cleavage; reactions run i n refluxing CHCI3 or i n the presences of thallium chloride, which was used successfully to promote the bromination of p o l y s t y r e n e , lead to s i g n i f i c a n t l y degraded products. If poly(3methylarylene ether sulfone), 22, i s employed as the substrate, bromination can be directed either to the aromatic ring, 23^ or to the benzyl position, 24, by controlling the bromination conditions. Attack at the benzyl position i s promoted by photolysis of the halogen or u t i l i z a t i o n of N-bromosuccinimide i n the presence of free r a d i c a l i n i t i a t o r s . 25

26

9

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

16

CHEMICAL REACTIONS ON POLYMERS

N i t r a t i o n and Reduction. In conjunction with a project involving N-carboxyanhydride (NCA) interaction with aminopropylcellulose to produce peptide grafts, we sought to produce soluble, well characterized polymers with primary amine substituents. The project proved to be one of the challenges associated with modification of condensation polymers. Two substituents were targeted, 3-amino- and 3-aminomethyl, as a primary amine function was needed to i n i t i t a t e NCA polymerization. Polymers with 3-amino substituents were to be produced simply by reduction of the corresponding 3-nitro derivatives. The usual n i t r a t i n g agents for aromatic compounds, i . e . fuming n i t r i c acid or n i t r i c - s u l f u r i c acid mixtures tend to decompose condensation polymers. However, C r i v e l l o has reported that mixtures of metal nitrates i n t r i f l u o r o a c e t i c anhydride promote n i t r a t i o n of poly(aryl carbonate)s and poly(phenylene oxide)s, only i n the case of the polycarbonates wa s i g n i f i c a n t los f molecula weight during the modification procedure to nitrate poly(arylen effect of n i t r a t i o n on the hydrolytic s t a b i l i t y of the corresponding derivatives. Derivatives with D.F.'s up to two are produced under very mild conditions, but some reduction i n molecular weight was observed. The chain cleavage was promoted by the acid medium; surprisingly, i n the presence of basic nucleophiles l i k e sodium methoxide, l i t t l e change i n hydrolytic s t a b l i t y r e l a t i v e to that of the unsubstituted polymer was observed. 27

-

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—

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-

©

—

-

©

-L^

-

î

NO» THF

-

€

H

-

ù

•"-"2/

/ /un AC

I

CH.

-

©

-

>

2

-

&

—

© NH

16.

-

{ "

Ο

" '

2

0

Bz-0-Ç-CH CH 2

0

2 v t e C

I

^S

THF

0

CH. I

25

/ NH

CH -τ

0

CH CH 2

2

£-O-Bz 0

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

1.

DALY ET AL.

17

Modification of Condensation Polymers

Nitrated poly(arylene ether sulfone), 15, proved to be remarkably resistant to reduction. No amino functions could be detected following treatment of the nitrated polymers with sodium d i t h i o n i t e , sodium borohydride, lithium aluminum hydride, palladium and sodium borohydride or low pressure hydrogénation. However, _15 can be reduced with stannous chloride and hydrochloric acid i n refluxing THF to the corresponding poly(aromatic amine), 16^. The 3amino derivative dissolved readily i n THF and CHCI3 and i n t r i n s i c v i s c o s i t y measurements indicated that l i t t l e change i n the molecular weight occurred during the reduction. We have shown that NCA s can be grafted to 16^ to produce soluble graft copolymers, ^5, and are currently working on the conditions to control the extent of grafting. The nitrated model compound, _9, proved even more resistant to reduction than the polymeric analog; the dissolving metal technique used to reduce _L5 f a i l e d on 9_ , but f i n a l l y the amino model, 10, was produced by treatment of 9^ with 25-fold f sodiu borohy dride. Compound JO serve polymerization. 1

Chloromethylation We have developed techniques for controlled chloromethylation of condensation polymers containing oxyphenyl repeating units. The chloromethylation can be effected with chloromethyl methyl ether, or l,4-bis-(chloromethoxy)butane i n the presence of stannic chloride. More recently we have been evaluating a mixture of chloromethyl ether and methyl acetate, produced by mixing acetyl chloride with dimethoxymethane i n the presence of a c a t a l y t i c amount of methanol, as a chloromethylating agent. Since the active chloromethyl ether i s produced s e l e c t i v e l y and the reaction mixture can be used d i r e c t l y , the procedure minimizes exposure to potential carcinogens. However, the presence of methyl acetate which i s formed as a by-product i n the reaction, moderates the a c t i v i t y of the chloromethylating agent s i g n i f i c a n t l y (Table I I ) . Note that polystyrene does not react with this reagent under conditions which are effective i n introducing chloromethyl groups on more activated aromatic rings. During the chloromethylation process, gelation occurs at high degrees of conversion, unless an effort i s made to maximize polymer d i l u t i o n and the concentration of chloromethylating reagent. Although soluble derivatives with D.F.'s less than 1.5 can be produced using a chloromethyl ether to substrate ratio of 10:1, a 20:1 ratio i s required to eliminate crosslinking as the D.F. approaches 2.0. Selection of the proper catalyst also minimizes the extent of concomitant crosslinking reactions. Evaluation of a series of Lewis Acid catalysts by comparing the extent of active chloride introduction on poly(arylene ether sulfone) within one hour at 110°C established the following order of r e a c t i v i t y : SbCls > AsCl3 > SnCli* > ZnCl2 > AICI3 > TiCli+ > SnCl2 > FeCl3Poly(2,6-dimethylphenylene oxide) exhibits a unique dependence upon the nature of the catalyst 1 6

20

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

18

because the phenoxy ether backbone tends to form stable inactive catalysts with each Lewis acid described above except stannic chloride. This fact, coupled with the r e l a t i v e l y small broadening of the molecular weight d i s t r i b u t i o n observed when stannic chloride was employed as the catalyst i n poly(arylene ether sulfone) modifications, prompted us to select stannic chloride as the general catalyst for choromethylation of condensation polymers. T a b l e II. Chloromethylation of Condensation P o l y m e r s Polymer

Reagent

Reactant Ratio

( Ιη] )

Temp( C) Time(h)

Reagent: Polymer: S n C l

% Subst (DF)

[η]

4

PPO, 2 (0.50)

CH 0CH Cl 3

e

2

1,4-bis

d

10

0.1

2

05

b

b

0.54

60

100(1.0)

25

97(0.97)

96

60(1.2)

96

95(1.9)

0.51

113

75(1.5)

0.65

110

96(1.9)

85

100(2.0)

90

100(2.0)

Poly(Ary1ene ether s u l f o n e ) , (0.51)

CH 0CH Cl 20

0.1

20

0.1

10

0.1

4.2

0.5

20

0.1

e

3

2

',4-bis

d

C

C

C

C

0.51

Sulfone Model, 7 CH 0CH C1 3

2

8

C

A c e t y l a t e d Phenoxy Resin (0.53)

CH 0CH C1 3

e

2

20

0I

C

0.45

Polystyrene CH 0CH Cl 3

2

1,4-bis

d

a

10 3.6

1.3

d

50

24

25

17

100(1.0)

a) 50:50 mixture of chloromethyl methyl ether and methyl acetate, b) solvent, c h l o r o f o r m ; c) solvent, tetrachloroethone; d) 1,4-bis(chloromethoxy)butane.

The substrate catalyst r a t i o plays an important role i n c o n t r o l l i n g reaction s e l e c t i v i t y ; a 1 0 : 1 substrate:catalyst r a t i o provided an acceptable balance between the rate of active chloride introduction and the extent of crosslinking. Table II summarizes the conditions required to prepare derivatives of p o l y ( o x y - 2 , 6 - d i m e t h y l - l , 4 phenylene), polysulfone, and phenoxy resin with varying degrees of active s i t e s . Comparison of the i n i t i a l v i s c o s i t i e s of the polymer substrates with those of the derivatives indicates that l i t t l e v a r i a t i o n i n the molecular weight has occurred during the modification. Condensation polymers composed of deactivated aromatic rings, i . e . polycarbonates, polyesters or polyamides undergo chloromethylation only i n the presence of stoichiometric amounts of Lewis acid catalysts; the reaction i s accompanied by s i g n i f i c a n t reductions i n the molecular weight. '

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

1. D A L Y E T A L .

Modification

of Condensation Polymers

19

The chloromethylated polymers are very reactive substrates for nucleophilic attack; further elaboration can be accomplished under homogeneous conditions i n aprotic solvents, or under heterogeneous conditions i n the presence of phase transfer c a t a l y s t s . The following examples are representative of approaches to functiona l i z e d condensation polymers via chloromethylated intermediates. Aminomethylation Conversion of chloromethylated polymers to our second target system, aminomethylated polymers, was approached i n several d i f f e r e n t ways. Two of the approaches, which were used successfully to convert model compound _11_ to the desired aminomethyl products f a i l e d when applied to the polymer system. The f i r s t of these, the Delépine reaction, appeared to be the most reasonable and economical, but only insoluble, apparently crosslinked products could be i s o l a t e d .

P a r t i a l l y Hydrolysed Insoluble Product The Delépine reaction involves nucleophilic displacement of active halides by hexamethylenetetramine, followed by hydrolysis of intermediate quaternary ammonium salt to release the amine. Normally the reaction i s useful for the conversion of a l k y l halides to primary amines without concomitant formation of secondary amines. Treatment of polymer 17 with hexamethylenetetramine i n a mixture of ethanol/THF afforded an insoluble r e s i n . Using diazabicyclooctane (DABCO), we demonstrated that the reaction could be limited to attack by a single nitrogen i n a multifunctional amine, so we did not anticipate crosslinking via bis-quat s a l t formation. Hydrolysis of 26^ with anhydrous HC1 i n ethanol generated free amino groups as evidenced by a positive ninhydrin test, but quantitative hydrolysis could not be achieved and the product remained insoluble. One would have expected a simple bis-quat to hydrolyse and open the crosslinked structure. 29

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

Reduction of azides i s a c l a s s i c a l approach to primary amine synthesis. Treatment of _17 with sodium azide i n DMF or i n THF/H2O mixtures i n the presence of phase transfer catalysts effects a quantitative conversion to the corresponding polymeric azide, 27. Recently the reduction of azides to primary amines v i a hydrolysis of iminophosphoranes produced by interaction of the azide with t r i e t h y l phosphite was r e p o r t e d . Application of this technique to the azidomethyl polymer, 27, as shown below, f a i l e d to produce a soluble polyamine. 30

Insoluble Resin The most successful approach to producing an aminomethyl derivative was the Gabriel synthesis. A phthalimide substituent can be introduced by Sn2 displacement of the chloride on _17^ with potassium phthalimide under homogeneous conditions i n DMF. The reaction i s quantitative i n a l l D.F. ranges and the phthalimidomethyl intermediates, 18, are quite soluble i n organic solvents.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

1.

DALY ET AL.

Modification

of Condensation Polymers

21

Direct aminomethylation of _1 or _2 can be effected by phthalimidomethylation with N-hydroxymethylphthalimide in t r i f l u o r o a c e t i c acid; however, some reduction i n the molecular weight of the substituted polymers can be detected by v i s c o s i t y measurements when the e l e c t r o p h i l i c phthalimidomethylation procedure i s employed. The aminomethyl substituent i s released by hydrazinolysis of the phthalimide substituents i n mixtures of THF/ethanol. The mixed solvent system was necessary; hydrazinolysis i n pure ethanol f a i l e d to remove the blocking groups quantitatively. Interestingly, the s o l u b i l i t y of the aminomethyl polymer, 19, depends upon the D. F. Polymers, which are soluble in THF, are formed i f the D.F. does not exceed 1. Using _19^ with a D.F. - 1.0, NCA's were allowed to react at various NCA/amine r a t i o s . A l l graft copolymers of _19 and the NCA of benzyl glutamate were soluble i n pyridine and DMSO. Polymers with short grafts 1-3 peptide units, were also soluble i n CHC13The most interesting aminomethyl derivative of condensation polymers that we have prepared t dat i derived fro direct reduction of poly(2-cyano-l,3-phenylen Enchainment of benzonitril 2,6-dichlorobenzonitrile with the potassium salt of bisphenol-A; copolymers with lower n i t r i l e contents can be produced by copolycondensation of bisphenol-A, 2,6-dichlorobenzonitrile and 4,4 -dichlorodiphenyl s u l f o n e . The pendent n i t r i l e function provides an active s i t e for further elaboration. Vie have shown that cyanoethylcellulose can be reduced to aminopropylcellulose using borane complexes. However, polymer 20 could not be reduced under similar conditions. The more powerful reducing agent, LAH, was required to effect the reduction of the enchained benzonitrile. Addition of a THF solution of 20^ to a solution of LAH i n THF produced a homogeneous reaction mixture, but, within one hour, the reduced polymeric complexes began to p r e c i p i t a t e . We used high d i l u t i o n techniques and long reaction times to assure complete reduction. Isolation of the desired poly(2aminomethyl-1,3-phenylene arylene ether), 21, was complicated by the formation of polyamine-metal complexes and a gelatinous precipitate of hydroxides. The multistep i s o l a t i o n procedure required to free the polyamine of metal ions reduced the actual yields of 21_ to about 70%. Both 20^ and n _ a r e soluble i n CHCI3; the i n t r i n s i c v i s c o s i t i e s of the two polymers were 0.59 and 0.30 dl/g, respectively. Thus, the reduction appears to be accompanied by some chain cleavage. 3 1

f

21

31

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

The s o l u b i l i t y properties of 21^ render i t an excellent support for benzyl glutamate g r a f t i n g . Reaction of various ratios of NCA/amine ratios yielded grafts of the predicted chain length. The graft copolymers were completely soluble i n THF and CHCI3 and could be cast into films. The unique properties of these materials are under investigation. Conclusions Among the condensation polymers derived from bisphenol-A, poly(arylene ether sulfone) exhibits the best balance between r e a c t i v i t y and backbone s t a b i l i t y for subsequent modification. We have shown that e l e c t r o p h i l i c substitution of the aryleneoxy units, i . e . bromination, n i t r a t i o n and chloromethylation, can be achieved. Introduction of amino and aminomethyl substituents provides a nucleophilic resin with applications i n ion-exchange and graft polymerization technology. A l l of the modified poly(arylene ether sulfone)s can be t int membranes furthe h will focus on the permselectivit

Literature Cited 1. Merrifield, R. B. J. Am. Chem. Soc. 1963, 85, 2149. 2. Bailey, D. C.; Langer, S. H. Chem. Rev. 1981, 82, 109; Frechet, J. M. J. Tetrahedron 1981, 37, 663; Akelah Α.; Sherrington, D.C. Polymer, 1983, 24, 1369; and references cited therein. 3. Polymer Supported Reactions in Organic Synthesis; Hodge, P.; Sherrington, D. C. Eds. Wiley: New York, 1980; Mathur, Ν. K.; Narang, C. K.; Williams, R. E. Polymers as Aids in Organic Chemistry; Academic: New York, 1980; Polymeric Reagents and Catalysts; Ford, Warren T., Ed.; ACS Symposium Series 308; American Chemical Society: Washington, DC, 1986. 4. Correct IUPAC nomenclature:poly(oxy-2,6-dimethyl-1,4-pheylene), PPO, poly(oxy-1,4-phenylenesulfonyl-1',4'-phenyleneoxy-1",4" phenylene (1'''-methylethylidene)-1''',4'''-phenylene), poly(arylene ether sulfone), and poly(oxy-(2-hydroxytri­ methylene) oxy-1,4-phenylene(1'-methylethylidene)-1',4' phenylene), phenoxy resin. 5. Ford, Warren T. in Polymeric Reagents and Catalysts; Ford, Warren T., Ed.; ACS Symposium Series 308; American Chemical Society: Washington, DC, 1986; pp 247-285. 6. White, D. M.;Orlando,C.M.in Polyethers; Vandenberg, Ε.,Ed.; ACS Symposium Series 6; American Chemical Society: Washington, DC, 1975; pp 178-184. 7. Vollmert, B.;Schoene, W. Angew. Makromol. Chem. 1969, 7, 15. 8. Percec, S.; Li, G. Polymer Preprints 1986, 27(2),19. 9. Chalk, A. J.; Hay, A.S. J. Polym. Sci., Polym. Chem. Ed. 1969, 7, 691. 10. Xie, S.; MacKnight, W.J.; Karasz, F.E. J. Appl. Polym. Sci., 1984, 29, 2679. 11. Mohanraj, S.; Ford, Warren T. Macromolecules 1986, 19, 2470. 12. Noshay, Α.; Robeson, L. M. J. Appl. Polym. Sci. 1976, 20, 1885. 13. Huang, R. Y.; Kim, J.J. J. Appl. Polym. Sci. 1984, 29, 4017. 14. Ward,III, W.J.; Salemme, R.M. U. S. Patent 3 780 496, 1973. 15. Li, G. U. S. Patent 4 521 224, 1985. 16. Verdet, L.; Stille, J.K. Organometallics 1982, 1, 380.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

1. D A L Y E T A L .

Modification of Condensation Polymers

23

17. Daly, W. H.; Wu, S. J. in New Monomers and Polymers ed. by Culbertson, Bill M.; Pittman, C.U.; Plenum: New York, 1984, pp 201-222. 18. Daly, W. H. J. Macromol. Sci. Chem. 1985, A22, 713. 19. Percec, V.; Auman, B. C. Makromol. Chem. 1984, 185, 2319. 20. Amoto, J. S.; Karady, S.; Sletzinger, M.; Weinstock, L. M. Synthesis 1979, 970. 21. Mohanty, D. K.; Hedrick, J. L.; Gobetz, K. Johnson, B.C.; Yilgor, I.; Yang, R.; McGrath, J. E. Polymer Preprints 1982, 23(1), 284; Heath, D. R.;Wirth, J. C. U. S. Patent 3 730 946, 1973; Chem. Abstr. 1973, 77, P127232. 22. Johnson, R. N.; Farnham, A. G.; Clendinning, R.A.; Hale, W.F.; Merrian, C.N.J.Polym.Sci. Part A-l, 1967, 5, 2375. 23. Crivello, J. V. J. Org. Chem. 1981, 46, 3056. 24. Wu, S.J. Ph.D. Dissertation, Louisiana State University, December 1983. 25. Ohmae, I; Takeuchi Y.Japan Kokai 7,550,352 1975; Chem Abstr 1976, 84, P31968k. 26. Farrall, M. J.; Frechet 27. Rungaroonthaikul, C. Ph.D. Dissertation, Louisiana State University, May 1986. 28. Daly, W. H.; Chotiwana, S.; Nielson, R. A. Polymer Preprints 1979, 20, 835. 29. Blazevic, N.; Kolbah, D.; Belin, B.;Sunjic, V.; Kajfez, F. Synthesis 1979, 161. 30. Koziara, Α.; Osowska-Poacewicka, K.; Zawadski, S.; Zwierzak, A. Synthesis 1985, 202. 31. Daly, W. H.; Chotiwana, S.; Liou, Y-C. in Polymeric Amines and Ammonium Salts, ed. by Goethals, E. J., Pergamon: New York 1980, p 37. 32. Daly, W, H.; Munir, A. J. Polym. Sci. Polym. Chem. Ed. 1984, 22, 975. RECEIVED August 27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 2

Dimethylene Spacers in Functionalized Polystyrenes 1

Graham D. Darling and Jean M . J. Fréchet

2

Department of Chemistry, University of Ottowa, Ottowa, Ontario K1N 9B4, Canada

Modes of attachment of functional groups to crosslinked polystyrene are discussed (1). Attention is drawn to improved stability and catalysts incorporatin polystyrene aryl and functional group heteroatom, and the simplicity and versatility of their synthesis through high-conversion functional group modifications. B e g i n n i n g as ion-exchange r e s i n s (2), and blossoming as s u p p o r t s f o r s o l i d - p h a s e p e p t i d e s y n t h e s i s (3), f u n c t i o n a l i z e d p o l y s t y r e n e s have p r o g r e s s i v e l y expanded i n v a r i e t y and importance as i n s o l u b l e c a t a l y s t s o r r e a g e n t s i n the s e g r e g a t i o n , s e p a r a t i o n , p r o t e c t i o n , a c y l a t i o n , a l k y l a t i o n , dehydrohalogenation, o x i d a t i o n or reduction of s m a l l m o l e c u l e s , r e a c t i o n s which are o f t e n f o l l o w e d by s i m p l e p u r i f i c a t i o n and r e g e n e r a t i o n of the s o l i d phase (4-, j ) ) . C u r r e n t l y , most of t h e s e r e a c t i v e polymers are prepared from ( c h l o r o m e t h y l ) p o l y s t y r e n e , which i t s e l f i s e a s i l y made by c o n t r o l l e d f u n c t i o n a l i z a t i o n (_2, 6·) o f c o m m e r c i a l l y a v a i l a b l e s t y r e n e - d i v i n y l b e n z e n e copolymer. F a c i l e n u c l e o p h i l i c displacement of l a b i l e b e n z y l i c c h l o r i d e , f r e q u e n t l y under p h a s e - t r a n s f e r c o n d i t i o n s (_7), a l l o w s f u n c t i o n a l f r e e m o l e c u l e s b e a r i n g n u c l e o p h i l i c heteroatoms t o become a t t a c h e d t o the macromolecular m a t r i x . However, the new carbon-heteratom bonds formed i n t h e s e f u n c t i o n a l group m o d i f i c a t i o n s are themselves r e l a t i v e l y f r a g i l e , s i n c e resonance s t a b i l i z e s the p a r t i a l charges devel o p e d d u r i n g t h e i r r u p t u r e ( 8 , 9) as shown below. —(-CH -CH-}~ 2

^CH

2

~*X

1

Current address: IBM

2

Current address: Department of Chemistry, Cornell University, Ithaca, N Y 14853-1301

Almaden Research Laboratory, San Jose, C A 95114

0097-6156/88/0364-0024$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2.

DARLING A N D FRÉCHET

Dimethylene Spacers

25

Many examples o f such b e n z y l i c i n s t a b i l i t y are p r o v i d e d by c l a s s i c a l ( f r e e - m o l e c u l e ) o r g a n i c c h e m i s t r y , as w e l l as a few by t h e s m a l l e r and more s p e c i a l i z e d f i e l d o f polymer-supported r e a g e n t s and c a t a lysts. Hence: - B e n z y l i c q u a t e r n a r y phosphonium and ammonium s a l t s are d e a l k y l a t e d by m i l d h e a t i n g and/or n u c l e o p h i l i c a n i o n s , p a r t i c u l a r l y i o d i d e (9) and t h i o l a t e ( 1 0 ) , but a l s o h y d r o x i d e ( 1 1 ) . Most N - b e n z y l p y r i d i n i u m o r q u a t e r n a r y a r y l ammonium compounds are p a r t i c u l a r l y s u s c e p t i b l e ( 1 2 ) . Decompositions o f t h i s s o r t have s e r i o u s l y l i m i t e d the u s e f u l n e s s o f s o l i d p h a s e - t r a n s f e r c a t a l y s t s d e r i v e d from ( c h l o r o m e t h y l ) p o l y s t y r e n e (13, 1 4 ) . - B e n z y l groups are c l e a v e d from amines heated w i t h i n o r g a n i c a c i d s ( 1 5 ) , c a r b o x y l i c a n h y d r i d e s (16) o r cyanogen bromide ( 1 7 ) . A c i d s a l s o c a t a l y z e the d i s p r o p o r t i o n a t i o n o f benzylamine t o d i b e n z y l a m i n e and ammonia ( 1 8 ) . - N - b e n z y l - s u l f o n a m i d e s are c l e a v e d under " r e l a t i v e l y m i l d c o n d i t i o n s " w i t h potassium a l k o x i d ( 1 9 ) - B e n z y l e t h e r s are amongs (20). S i g n i f i c a n t c l i p p i n f u n c t i o n a l i t y , r e s u l t e d d u r i n g attempted H C l - c a t a l y z e d h y d r o l y s e s o f p o l y s t y r e n e - s u p p o r t e d o x a z o l i n e i n t e r m e d i a t e s ( 2 1 , 22) and c h i r a l s u p p o r t s (23, 2 4 ) . - Benzyl-type esters hydrolyze r e l a t i v e l y e a s i l y . This i s w e l l known f o r p o l y m e r i c systems (22, 25, 2 6 ) . - A c e t y l bromide c l e a v e s d i b e n z y l s u l f i d e , w h i l e d i e t h y l o r d i i s o propyl are r e s i s t a n t (27). - B e n z y l - s i l a n e s are n o t immune t o h y d r o x i d e o r o t h e r n u c l e o p h i l e s (28, 2 9 ) . - B e n z y l - n i t r o g e n , s u l f u r , o r -oxygen bonds are somewhat suscept i b l e t o h y d r o g e n o l y s i s , e i t h e r d u r i n g c a t a l y t i c hydrogénation (30, 3 1 ) , o r upon treatment w i t h L - s e l e c t r i d e ( 3 2 ) , o r even l i t h i u m a l u m i nium h y d r i d e ( 3 3 ) . Thus, the chemist or c h e m i c a l engineer may l e g i t i m a t e l y f e a r f u r t h e r a t t a c k by u n d e s i r e d n u c l e o p h i l e s on b e n z y l i c carbon, as a main o r s i d e - r e a c t i o n i n the course of assembly, a p p l i c a t i o n o r r e g e n e r a t i o n o f many members of t h i s s t r u c t u r a l c l a s s o f f u n c t i o n a l polymer, l e a d i n g t o l o s s o f r e a c t i v e s i t e s o r mobile groups from t h e s o l i d phase. As t h e l a s t s t e p o f a s o l i d - p h a s e s y n t h e s i s , such as t h a t o f p o l y p e p t i d e s by M e r r i f i e l d , c o n t r o l l e d s e p a r a t i o n o f pendant from p o l y s t y r e n e support may even be u s e f u l (_3, 25) — b u t g e n e r a l l y such d e c o m p o s i t i o n o f a r e a c t i v e polymer o n l y s e r v e s t o d e a c t i v a t e i t w h i l e i n t r o d u c i n g contaminants t o both s o l i d and l i q u i d phases. I n a d d i t i o n , o x i d a t i o n (15, 34) or a l k y l a t i o n (35, 36) may take p l a c e a t b e n z y l i c methylene carbons made p a r t i c u l a r l y a c i d i c by b e i n g bound a t once t o a r y l and e l e c t r o n - w i t h d r a w i n g groups or p o l a r i z a b l e secondrow elements. D i r e c t c o n n e c t i o n of pendant heteroatom t o p o l y s t y r e n e a r y l i s a s y n t h e t i c a l l y more d i f f i c u l t , but o f t e n s t i l l f e a s i b l e ( 3 7 ) , a l t e r n a t i v e . However, though bonds from phenyl t o many common heteroatoms are r e l a t i v e l y s t r o n g , resonance s t a b i l i z a t i o n o f p a r t i a l p o s i t i v e charge developed on an a r y l a t e d atom a c t i v a t e s i t t o l e a v e o t h e r s u b s t i t u e n t s : a l k y l a n i l i u m s a l t s (12) and a n i l i n e s ( 3 8 ) , as w e l l as p h e n o l i c e s t e r s ( 3 9 ) , a r e r e l a t i v e l y easy t o c l e a v e . A r y l l i n k a g e s ,

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26

CHEMICAL REACTIONS ON POLYMERS

r e s o n a t i n g w i t h r e a c t i o n p r o d u c t s , make many non-metal atoms e a s i e r t o o x i d i z e . More e l e c t r o p o s i t i v e elements, such as s i l i c o n ( 4 0 ) , a r e e a s i l y d i s p l a c e d from phenyl by p r o t o n s and o t h e r L e w i s a c i d s through e l e c t r o p h i l i c a r o m a t i c s u b s t i t u t i o n . Furthermore, an a n t i p o d a l e l e c ­ t r o n - w i t h d r a w i n g group can a c t i v a t e b e n z y l hydrogen on t h e polymer backbone f o r i n o p p o r t u n e i o n i c o r r a d i c a l s i d e - r e a c t i o n s ( 4 1 ) . On t h e o t h e r hand, i n s e r t i n g even one more methylene group between polymer and pendant would r e s u l t i n a primary bond n e i t h e r u n s t a b l e nor d e s t a b i l i z i n g towards n u c l e o p h i l e s , p e r m i t t i n g a c h e m i c a l l y more r o b u s t working m o l e c u l e w h i l e r e t a i n i n g t h e a t t r a c t i v e p h y s i c a l p r o ­ p e r t i e s of p o l y s t y r e n e r e s i n . A d d i t i o n a l l y , e x t e n d i n g a r e a c t i v e s i t e f u r t h e r from polymer backbone improves c o n t a c t w i t h f r e e sub­ s t r a t e i n t h e l i q u i d phase (4-2, 43) , as w e l l as w i t h s i m i l a r f u n c t i o ­ n a l neighbours t o enhance a c o o p e r a t i v i t y e f f e c t ( 4 4 ) , f o r an o v e r a l l i n c r e a s e i n c a t a l y t i c o r o t h e r a c t i o n . F o r example, among both polymers and f r e e m o l e c u l e s c o n t a i n i n g a p h e n e t h y l s u b s t r u c t u r e i t has been observed t h a t : - 2-phenethyl-halopyridiniu t o t h e i r b e n z y l , and even methyl o r e t h y l , c o u n t e r p a r t s (45, 4 6 ) ; - N-benzyl-N-phenethyl-N,N-dimethylammonium c h l o r i d e l o s e s predo­ m i n a n t l y b e n z y l when heated w i t h t h i o p h e n o x i d e , g i v i n g s t a b l e N,Ndimethylphenethylamine (47); - Ν,Ν-dimethylphenethylamine i t s e l f i s i n e r t t o f u r t h e r t r e a t m e n t w i t h hot a c e t i c anhydride (48); - s i m p l e c a r b o x y l i c a c i d s can be a l k y l a t e d (26) or p h o t o c h l o r i nated ( 4 9 ) , cinnamates p h o t o c r o s s l i n k e d (50) and t - b u t y l c a r b o n y l a t e d amino a c i d s d e p r o t e c t e d by a c i d o l y s i s ( 5 1 ) , w h i l e r e m a i n i n g e s t e r i f i e d t o p o l y s t y r e n e v i a dimethylene s p a c e r ; - q u a t e r n a r y phosphonium s a l t s connected through dimethylene s p a c e r s a r e s t a b l e r and more a c t i v e p h a s e - t r a n s f e r c a t a l y s t s than b e n z y l i c ones f o r r e a c t i o n o f c y a n i d e or t h i o l a t e w i t h a l k y l h a l i d e s ; r a t e s f u r t h e r improve w i t h even l o n g e r s p a c e r s (52, 5 3 ) ; - p h e n e t h y l - s u p p o r t e d p o l y s t y r y l t a r t a r a t e , f u n c t i o n n i n g as a s t a b l e s o l i d - p h a s e c h i r a l a u x i l i a r y f o r t h e S h a r p l e s s e p o x i d a t i o n of a l l y l i c a l c o h o l s , g i v e s h i g h e r c h e m i c a l and o p t i c a l y i e l d s than i t s b e n z y l i c analogue ( 5 4 ) ; I n t r o d u c t i o n o f dimethylene s p a c e r s onto p o l y s t y r e n e . Most of t h e t e c h n i q u e s and r e a c t i o n s d e s c r i b e d below, though o f t e n a p p l i c a b l e t o s o l u b l e p o l y s t y r e n e have been o p t i m i z e d u s i n g a 1% d i v i n y l b e n z e n e c r o s s l i n k e d g e l . To s i m p l i f y n o t a t i o n s , such a polymer h a v i n g 20% of i t s a r o m a t i c groups s u b s t i t u t e d w i t h f u n c t i o n a l group Ζ would be r e p r e s e n t e d as shown below and be g i v e n t h e molecul a r formula: ( C H ) .(C H ) .(C H Z) . 1 0

1 0

0 - 0 1

8

8

0 7 9

8

7

0 - 2 0

^CH-CH^ DF :

0.20

© - 1

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2.

DARLING A N D FRÉCHET

Dimethyiene Spacers

F u n c t i o n a l i z a t i o n through hydroxyethyl

27

group.

A d i m e t h y i e n e s p a c e r , t e r m i n a t e d by a v e r s a t i l e h y d r o x y l "handle", i s e a s i l y i n t r o d u c e d onto commercial c r o s s l i n k e d p o l y s t y r e n e r e s i n , w i t h o u t rearrangement (55) o r g r a f t i n g o f e t h y l e n e g l y c o l oligomer ( 5 6 ) , by t r e a t i n g the c o l d l i t h i a t e d polymer w i t h e x c e s s e t h y l e n e o x i d e ( 3 7 ) . The r e s u l t i n g ( h y d r o x y e t h y l ) p o l y s t y r e n e i s v i r t u a l l y i d e n t i c a l t o product made l e s s s i m p l y by c y a n a t i o n / h y d r o l y s i s / reduct i o n o f commercial ( c h l o r o m e t h y l ) p o l y s t y r e n e (52, 5 7 ) , o r by c o p o l y m e r i z a t i o n o f s t y r e n e , d i v i n y l b e n z e n e and t h e p r o t e c t e d f u n c t i o n a l monomer (26, 5 8 ) . P a s t e f f o r t s t o prepare p o l y s t y r e n e s p o s s e s s i n g l o n g e r f u n c t i o n a l i z e d o l i g o m e t h y l e n e s p a c e r s , by F r i e d e l - C r a f t s a l k y l a t i o n o f d i h a l i d e s , o r r e a c t i o n o f d i h a l i d e s o r c y c l i c halomium i o n s w i t h m e t a l l a t e d polymer, have g e n e r a l l y been accompanied by s i g n i f i cant a d d i t i o n a l c r o s s l i n k i n g o f polymer networks (53, 59, 6 0 ) . A r e c e n t e x c e p t i o n i s Tomoi e t a l ' s (61) a l k y l a t i o n o f s o l u b l e or c r o s s l i n k e d p o l y s t y r e n e w i t h w-bromoalkenes c a t a l y z e d b 30 mol% trifluoromethanesulfoni which i s r e p o r t e d t o procee d e c o m p o s i t i o n o f polymer backbone. ( H y d r o x y e t h l y ) p o l y s t y r e n e has p r e v i o u s l y been f u r t h e r f u n c t i o n a l i z e d w i t h o u t b r e a k i n g the C-0 bond, by t r a n s e s t e r i f i c a t i o n ( 5 4 ) , o r by c a r b o x y l i c a c i d w i t h d i c y c l o h e x y l c a r b o d i i m i d e ( 5 1 ) , o r by a c i d anhydride ( 5 8 ) , o r by a c y l h a l i d e s (26, 49) or c h l o r o d i a l k y l p h o s p h i t e s o r phosphines (50) and a c i d a c c e p t o r . D e r i v a t i z i n g with 3 , 5 - d i n i t r o b e n z o y l c h l o r i d e i n p y r i d i n e , f o l l o w e d by n i t r o g e n a n a l y s i s , i s a r e l i a b l e way o f a s s a y i n g polymer-bound h y d r o x y l (37, 5 7 ) . A l k y l a t i n g and a r y l a t i n g r e a g e n t s (62) a l s o r e a c t w i t h p o l y m e r i c a l c o h o l i n a s t r a i g h t f o r w a r d manner. For ( h y d r o x y e t h y l ) p o l y s t y r e n e t o succeed as a v e r s a t i l e s y n t h e t i c i n t e r m e d i a t e ( 5 7 ) , t e c h n i q u e s must be e v o l v e d t o r e p l a c e oxygen by o t h e r atoms w h i c h may be more s u i t e d t o good f u n c t i o n o f f i n a l reagent. Such c o n v e r s i o n s must be c o m p l e t e l y q u a n t i t a t i v e , s i n c e unr e a c t e d , s i d e - r e a c t e d o r o v e r - r e a c t e d f u n c t i o n a l i t i e s cannot be removed from the s o l i d p r o d u c t , and may u l t i m a t e l y i n t e r f e r e w i t h i t s destined a c t i v i t y . N u c l e o p h i l i c s u b s t i t u t i o n a t 2-phenethyl under SN1 c o n d i t i o n s i s o c c a s i o n a l l y accompanied by a c u r i o u s s c r a m b l i n g o f both methylene c a r b o n s , a t t r i b u t e d by some t o t h e i n t e r m e d i a c y o f a n o n c l a s s i c a l three-membered carbonium i o n ; however, s i n c e t h e consequences a r e o n l y d e t e c t a b l e i n i s o t o p i c a l l y - l a b e l l e d m o l e c u l e s , the m e c h a n i s t i c d e t a i l i s moot ( 6 3 ) . The a l k e n e b e i n g c o n j u g a t e d , e l i m i n a t i o n c a n be a more i m p o r t a n t s i d e - r e a c t i o n o f p h e n e t h y l f u n c t i o n a l i t i e s than w i t h many o t h e r s . F o r t u n a t e l y , i t s o c c u r r e n c e d u r i n g f u n c t i o n a l group m o d i f i c a t i o n c a n o f t e n be a v o i d e d by c a r e f u l c h o i c e o f r e a c t i o n s t r a t e g y and c o n d i t i o n s ; f o r example, by choosing t o s y l a t e as a l e a v i n g group (64, 6 5 ) , and by w o r k i n g i n p o l a r s o l v e n t s a t low o r moderate t e m p e r a t u r e s w i t h s t r o n g n u c l e o p h i l e s t h a t are a l s o weak bases ( 6 6 ) . T h i s k i n d o f d e c o m p o s i t i o n i s n o t a problem f o r most t a r g e t polymer r e a g e n t s and c a t a l y s t s , whose f i n a l f u n c t i o n a l i t i e s are g e n e r a l l y poor l e a v i n g groups under b a s i c c o n d i t i o n s .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

F u n c t i o n a l i z a t i o n t h r o u g h t o s y l o x y e t h y l _grou£. ( C h l o r o e t h y l ) p o l y s t y r e n e s and ( i o d o e t h y l ) p o l y s t y r e n e s a r e each prepared from t h e a l c o h o l by common r e a g e n t s i n a s i n g l e s t e p w i t h o u t c o m p l i c a t i o n s , but one-pot procedures f a i l t o produce c o m p l e t e l y pure bromide, which must be prepared from t h e t o s y l a t e by a s s i s t e d h a l i d e exchange ( 5 7 ) . The p r e p a r a t i o n of ( t o l u e n e s u l f o n y l o x y e t h y l ) p o l y s t y r e n e i t s e l f , i f performed i n i c e - c o l d p y r i d i n e as f o r t h e f r e e analogue ( 6 4 , 6 5 ) , r e q u i r e d a week t o complete (67) i f q u a t e r n a r y ammonium and o t h e r s i d e - p r o d u c t s (68) a r e t o be a v o i d e d . I n c o n t r a s t , w i t h n o n - n u c l e o p h i l i c d i i s o p r o p y l a m i n e (69) as a c i d a c c e p t o r i n s t e a d o f p y r i d i n e , ( h y d r o x y e t h y l ) p o l y s t y r e n e and t o l u e n e s u l f o n y l c h l o r i d e need o n l y be r e f l u x e d i n carbon t e t r a c h l o r i d e f o r a few hours t o g i v e t h e d e s i r e d t o s i c e s t e r as s o l e product i n q u a n t i t a t i v e y i e l d (57).

T o s y l a t e i s d i s p l a c e d by weak oxyanions w i t h l i t t l e e l i m i n a t i o n i n a p r o t i c s o l v e n t s , p r o v i d i n g a l t e r n a t i v e r o u t e s t o polymer-bound e s t e r s and a r y l e t h e r s . A l k o x i d e s , u n f o r t u n a t e l y , g i v e s i g n i f i c a n t f u n c t i o n a l y i e l d s of ( v i n y l ) p o l y s t y r e n e under t h e same c o n d i t i o n s . Phosphines and s u l f i d e s can a l s o be prepared from t h e a p p r o p r i a t e anions ( 5 7 ) , t h e l a t t e r l i p o p h i l i c enough f o r p h a s e - t r a n s f e r c a t a l y s i s f r e e from p o i s o n n i n g by r e l e a s e d t o s y l a t e . T r a n s f o r m a t i o n s t o polymer-bound amino compounds, which a r e o f t e n u s e f u l as l i g a n d s f o r m e t a l s i o n s or o t h e r f r e e s p e c i e s ( 6 7 ) , employ a wide s e l e c t i o n of o r g a n i c r e a c t i o n s . Quaternary ammonium s a l t s r e s u l t from h e a t i n g i s o l a t e d polymer t o s y l a t e w i t h t e r t i a r y amine; they may a l s o be prepared i n one s t e p from ( h y d r o x y e t h y l ) p o l y s t y r e n e and t o l u e n e s u l f o n y l c h l o r i d e and a t w o - f o l d e x c e s s of amine. Secondary amines, such as p y r r o l i d i n e , must be a l k y l a t e d w i t h c a r e : too p o l a r a s o l v e n t l e a d s t o p a r t i c i p a t i o n of a second nearby polymer-bound a l k y l a n t i n t h e f o r m a t i o n of a q u a t e r n a r y ammonium s a l t , a l o n g w i t h t h e d e s i r e d i m m o b i l i z e d t r i a l k y l amine. The except i o n , as seen above, i s d i i s o p r o p y l a m i n e , w h i c h r e f u s e s t o d i s p l a c e t o s y l a t e even i n t h e r e f l u x i n g pure amine, o r i n h o t d i m e t h y l formamide o r o t h e r p o l a r s o l v e n t , w h i l e m e t a l d i i s o p r o p y l a m i d e i s n o t o r i o u s as a p o w e r f u l n o n - n u c l e o p h i l i c base. However, carboxamide i s n o t d i f f i c u l t t o form from ( c a r b o x y m e t h y l ) p o l y s t y r e n e , a g a i n u s i n g t o l u e n e s u l f o n y l c h l o r i d e as condensing agent; t h i s can then be reduced t o ( d i i s o p r o p y l - e t h y l a m i n o e t h y l ) p o l y s t y r e n e , w h i c h i s of i n t e r e s t as a polymer-bound n o n - n u c l e o p h i l i c base .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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DARLING A N D FRÊCHET

Dimethyiene Spacers

29

An amide a n i o n w i l l p r e f e r s u b s t i t u t i o n i f i t s b a s i c i t y i s s u f f i c i e n t l y lowered by resonance, and can be u s e f u l where t h e n e u t r a l nitrogen i s unreactive or otherwise u n s u i t a b l e . Quaternizat i o n cannot be prevented i n the a l k y l a t i o n o f even f r e e n e u t r a l i m i d a z o l e , but an i m i d a z o l i d e a n i o n w i l l match w i t h o n l y one of t h e e l e c t r o p h i l i c s i t e s t e r m i n a t i n g dimethyiene spacer on p o l y s t y r e n e .

P h t h a l i m i d e and N - a l k y l - t o l u e n e s u l f o n a m i d e s a l t s a r e s i m i l a r l y a l k y l a t e d , and c a n f u r t h e r m o r e be c l e a v e d t o polymer-bound secondary and p r i m a r y amines r e s p e c t i v e l y ( 5 7 ) . P o t a s s i u m p y r r o l i d o n i d e g i v e s polymer-bound t e r t i a r y amide, of i n t e r e s t as a s o l i d c o s o l v e n t catalyst;

I n c o n t r a s t , the a c y c l i c a n i o n s of N-methyl acetamide and N-methyl-ot o l u a m i d e p r e f e r p r o t o n s t o carbon, f o r c i n g an a l t e r n a t i v e approach such as a c y l a t i o n o f ( m e t h y l a m i n o e t h y l ) p o l y s t y r e n e . I t i s unfort u n a t e too t h a t 4-N-methyl-pyridinamide, whose c o n j u g a t e a c i d p r e f e r s a l k y l a t i o n on r i n g r a t h e r than s i d e - c h a i n n i t r o g e n , i s s i m i l a r l y t o o b a s i c and/or h i n d e r e d f o r good y i e l d s o f i m m o b i l i z e d d i a l k y l a m i n o p y r i d i n e a c y l a t i o n c a t a l y s t from ( t o l u e n e s u l f o n y l o x y e t h y l ) p o l y s t y r e n e though not from ( b r o m o p r o p y l ) p o l y s t y r e n e (Fréchet, J.M.J.; D e r a t a n i , Α.; D a r l i n g , G.D.; Macromolecules i n p r e s s ) , whose s y n t h e s i s from s p e c i a l t y monomer i s however more d i f f i c u l t f o r the g e n e r a l o r g a n i c l a b o r a t o r y . N e v e r t h e l e s s , t h i s i l l u s t r a t e s one o f t h e few cases where a t h r e e carbon spacer shows s i g n i f i c a n t advantages over i t s two carbon a n a l o g . A number o f s y n t h e t i c approaches were undertaken towards a polymer-bound v e r s i o n o f the v e r s a t i l e N - m e t h y l - 2 - h a l o p y r i d i n i u m c o n d e n s a t i o n agent developped by Mukaiyama ( 7 0 ) , a p h e n e t h y l s u b s t i t u t e d analogue o f w h i c h shows e x c e p t i o n a l s t a b i l i t y and poten­ t i a l f o r r e c y c l a b i l i t y (71) . P o l y m e r i c a l k y l a t i o n o f 2 - c h l o r o p y r i d i n e o r 2-methoxypyridine was i n c o m p l e t e due t o h i n d r a n c e and d e a c t i ­ v a t i o n o f h e t e r o c y c l i c n i t r o g e n , though the impure product s t i l l showed some d e h y d r a t i n g a b i l i t y ( 7 2 ) . A l t e r n a t i v e f o r m a t i o n o f 2p y r i d o n e by o x i d a t i o n (73) o f p y r i d i n i u m c h l o r i d e w i t h b a s i c f e r r i c y a n i d e was accompanied by s m a l l amounts o f c o l o u r e d r i n g - o p e n i n g (74) s i d e - p r o d u c t s . The same 2-pyridone c o u l d be o b t a i n e d by s t r o n g l y h e a t i n g p o l y m e r i c t o s y l a t e i n a l a r g e excess o f 2-methoxy­ p y r i d i n e as s o l v e n t , f o l l o w e d by h y d r o l y s i s . Conditions of f o r m a t i o n from the t r i m e t h y l s i l y l e t h e r of the 4-isomer, which ought t o d i s p l a y s i m i l a r behaviour by analogy w i t h the c o r r e s p o n d i n g f r e e m o l e c u l e s ( 7 5 ) , a r e m i l d e r and more e c o n o m i c a l . Treatment o f ( 4 p y r i d o n e t h y l ) p o l y s t y r e n e by t h i o n y l o r c a r b o n y l c h l o r i d e s , c o n c u r r e n ­ t l y w i t h m e t a t h e s i s by t e t r a f l u o r o b o r a t e l i p o p h i l i c c o u n t e r i o n , a f f o r d s a s o l i d - p h a s e reagent c a p a b l e o f t r a n s f o r m i n g a m i x t u r e o f a l c o h o l and c a r b o x y l i c a c i d t o the e s t e r . However, the measured

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

30

CHEMICAL REACTIONS ON POLYMERS

(PVCH.CH.N Θ

P)-CH CH OTs 2

2

N

0

OTs

7 7

OCH

ν

3

J

CHP (P>CH CH N 2

2

/

a c t i v i t y of t h e polymer i s somewhat l e s s than hoped f o r , p r o b a b l y due to l a c k of a c c e s s i b i l i t y o f s i t e s deep w i t h i n a polymer m a t r i x i n s u f ­ f i c i e n t l y s w o l l e n by o r g a n i c s o l v e n t s Undoubtedly c o n d i t i o n s can s t i l l be o p t i m i z e d f o r t h i

D e l i b e r a t e p r o d u c t i o n of ( v i n y l ) p o l y s t y r e n e from ( t o l u e n e s u l f o x y e t h y l ) p o l y s t y r e n e o r ( h a l o e t h y l ) p o l y s t y r e n e s was b e s t a c c o m p l i ­ shed by q u a t e r n i z a t i o n w i t h Ν,Ν-dimethylaminoethanol, f o l l o w e d by t r e a t m e n t w i t h base: b e t a - d e p r o t o n a t i o n i s encouraged i n t h e c y c l i c z w i t t e r i o n i c i n t e r m e d i a t e . R e a c t i o n was f a s t e r and c l e a n e r than w i t h o t h e r r e a g e n t s recommended ( 6 4 , 76, 77) f o r e l i m i n a t i o n s , such a s a l k o x i d e , d i a z a b i c y c l o u n d e c e n e or q u a t e r n a r y ammonium h y d r o x i d e ; t h i s new and e f f i c i e n t procedure may f i n d a p p l i c a t i o n elsewhere. H y d r o m e t a l l a t i o n or o t h e r a d d i t i o n s t o polymer-bound o l e f i n may prove u s e f u l s t e p s i n f u t u r e s y n t h e s e s by polymer m o d i f i c a t i o n . HO-CH

2

p V C H C H C I + Me NCH CH OH — • ( p V C H 2

2

2

2

2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CI

2.

DARLING AND

31

Dimethyiene Spacers

FRÉCHET

EXPERIMENTAL SECTION I n f r a r e d s p e c t r a of KBr p e l l e t s were measured on a N i c o l e t 10DX FTIR. E l e m e n t a l a n a l y s e s were performed u s i n g P a r r p e r o x i d e bombs and by MHW L a b o r a t o r i e s ( P h o e n i x , AZ). (Hydroxyethyl)polystyrene. ( 1 0 1 0 ) 0 . 0 1 - ( 8 8 ) 0 . 5 7 ' ( 8 7 ) 0 . 4 2 (Bromo)polystyrene (20.00 g, 60 meq), o r i g i n a l l y prepared from commercial 1% c r o s s l i n k e d p o l y s t y r e n e r e s i n ( 3 7 ) , was suspended i n 500 ml dry benzene under n i t r o g e n . Into t h i s p a l e orange s u s p e n s i o n was i n j e c t e d 2.2 M nBuLi/hexane (60 ml, 132 meq), and the whole was s t i r r e d a t 60°C f o r 3 h o u r s . The l i q u i d phase was removed by f i l t r a t i o n , and the b e i g e r e s i d u e , s t i l l under n i t r o g e n , was suspended i n 200 ml dry THF, and c o o l e d t o -50°C, b e f o r e r e c e i v i n g condensed e t h y l e n e o x i d e by i n j e c t i o n (9.5 ml, 190 meq), t h e n b e i n g f u r t h e hours w h i l e g r a d u a l l y warmin y e l l o w s u s p e n s i o n was t h e n f i l t e r e d , and t h e r e s i d u e washed 1 X THF:H 0 3:1, 1 X THF:H 0:conc HC1/H 0 8:2:1, 3 X H 0, 1 X THF, 2 X CH3OH, 1 X E t 0 , t h e n d r i e d under vacuum o v e r n i g h t : IR (KBr) peaks absent a t 1487, 1408, 1073, 1010, and 718 cm" f o r a r y l bromide p r e c u r s o r , and a t 1150-1060 cm" f o r ether side-products (CH -0-CH ); peaks p r e s e n t a t 3400 ( b r , CH 0-H) and 1046 ( s , CH -0) cm" . Anal. C

H

C

H

C

2

H

B r

2

2

2

2

1

1

2

2

1

2

Calcd for ( C H 0, 5.47; B r , 0. 1 0

C

1 0

2

H

C

H

:

C

) l « ( 8 8 ) o 57·( 10 12°)o 4 2 ' Found: C, 86.51; H, 8.05; θ", 5.51; 0

8 6

0

5 8 ;

' Br,

H

7

' 0.

'

9 6 ;

(3,5-dinitrobenzoyloxyethyl)polystyrene. ( 10 10)0.01'( 8 8)0.57-( 10 12°)0.42 ( H y d r o x y e t h y l ) p o l y s t y r e n e (0.13 g, 0.44 meq),was heated w i t h 3 , 5 - d i n i t r o b e n z o y l c h l o r i d e (0.13 g, 0.55 meq) i n 2 ml dry p y r i d i n e a t 100°C under n i t r o g e n f o r 2 h o u r s , t h e n t h e y e l l o w - g r e e n s u s p e n s i o n was f i l t e r e d , and the r e s i d u e washed 3 X H 0, 1 X MEK, I X C H C 1 , 2 X CH3OH, and d r i e d under vacuum o v e r n i g h t , y i e l d i n g 0.20 g of a p a l e y e l l o w - b e i g e powder: IR (KBr) peaks absent a t 3400 and 1046 cm" f o r alcohol precursor; peaks p r e s e n t a t 3098 (w, A r - H ) , 1733 ( s , C=0), 1547 ( s , A r - N 0 ) , 1344 ( s , A r - N 0 ) , 1277 ( s , C0-0), 1164 (m, C0-0), 721 (m, A r - N 0 ) cm" . Anal. C

H

C

H

C

2

2

H

2

1

2

1

2

2

C

H

C

H

N

C a l c d f o r (C H )o.01·( 8 s)o.57-( 17 14 2°6)o.42 N, 5.66. 10

10

: Ν

'

5

·

7 6

·

F

o

u

n

d

:

(2,4-dinitrophenoxyethyl)polystyrene. ( 10 10)0.01-( 8 8)0.63'( 10 12°)0.36 ( H y d r o x y e t h y l ) p o l y s t y r e n e (0.51 g, 1.5 meq) was heated w i t h 2 , 4 - d i n i t r o f l u o r o b e n z e n e (0.30 ml, 2,4 meq) y e l l o w l i q u i d , and t r i e t h y l a m i n e (0.30 ml, 2.2 meq) i n 2 ml dry t o l u e n e a t 88°C f o r 40 h o u r s , then the dark r e d s u s p e n s i o n was f i l t e r e d , and the r e s i d u e washed 3 X acetone u n t i l f i l t r a t e was c o l o u r l e s s , 3 X H 0, 1 X MEK, I X C H C 1 , 2 X CH3OH, and d r i e d under vacuum o v e r n i g h t , y i e l d i n g 0.74 g of b r i g h t y e l l o w powder: IR (KBr) peaks absent a t 3400 and 1046 cm" for alcohol precursor; peaks C

H

C

H

C

H

2

2

2

1

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

32

CHEMICAL REACTIONS ON POLYMERS

p r e s e n t a t 1609 ( s , A r - N 0 ) , 1536 ( s , A r - N 0 ) , 1344 ( s , A r - N 0 ) , 1287 ( s , A r - N 0 ) , 1152 (m, C H - 0 A r ) , 1087 (m, C H - 0 A r ) , 833 (m, Ar-H) cm" for d e s i r e d product. 2

2

2

1

2

2

2

(Toluenesulfonyloxyethyl)polystyrene. C

H

C

H

C

H

( 1 0 l o ) o . 0 1 - ( 8 9 ) o . 7 0 ' ( 1 0 1 2 % . 2 9 (Hydroxyethyl)polystyrene (10.35 g, 35 meq), t o l u e n e s u l f o n y l c h l o r i d e (8.4 g, 44 meq), and d r y d i i s o p r o p y l a m i n e (10 m l , 71 meq), were s t i r r e d t o g e t h e r i n 70 ml carbon t e t r a c h l o r i d e under n i t r o g e n a t room temperature, then heated t o r e f l u x f o r 6 hours. The p a l e y e l l o w s u s p e n s i o n was f i l t e r e d , and the r e s i d u e washed 1 X acetone, 3 X H 0 , 1 X MEK, I X C H C 1 , 2 X E t 0 , and d r i e d under vacuum o v e r n i g h t t o y i e l d 14.28 g of a v e r y p a l e y e l l o w powder: IR (KBr) peaks absent a t 3400 and 1046 cm" f o r a l c o h o l p r e c u r s o r ; peaks p r e s e n t a t 1363 ( s , S0-0C), 1180 ( d o u b l e t , s, S0-0C), 1098 (m C - 0 ) 964 ( s S-0-C) 905 (m S-0-C) 815 (m, S-0-C), 760 (m, S 0 ) cm" . A n a l . C a l c d f o 5,74; N, 0. Found: 9, 5,73; N, 0. 2

2

2

2

1

3

(3-nitrophenoxyethyl)polystyrene. C

H

C

H

C

H

S 0

( 10 10)0.01-( 8 8)0.70( 17 18 3)0.29 (Toluenesulfonyloxyethyl)poly­ s t y r e n e (0.51 g, 0.91 meq), m - n i t r o p h e n o l p a l e y e l l o w c r y s t a l s (0.25 g, 1.8 meq) and anhydrous potassium carbonate (0.26 g, 2.0 meq) were s t i r r e d i n 5 ml d r y dimethylformamide under n i t r o g e n a t 60°C f o r 16 hours. The r e d s u s p e n s i o n was f i l t e r e d , and t h e r e s i d u e washed 1 X acetome, 3 X H 0 , 1 X MEK, I X C H C 1 , 2 X CH3OH, and d r i e d under vacuum o v e r n i g h t t o g i v e a p a l e y e l l o w powder: IR (KBr) peaks absent a t 1363 and 1176 cm f o r t o s i c e s t e r p r e c u r s o r ; peaks p r e s e n t a t 1531 ( s , A r - N 0 ) , 1351 ( s , A r - N 0 ) , 1245 (m, C H - 0 A r ) , 1029 (m, C H ~ OAr) and 738 (m, Ar-H) cm" . A n a l . C a l c d f o r 2

2

2

2

2

2

2

1

C

H

C

H

C

H

N 0

( 10 10)0.01-( 8 8)0.70-( 16 15 3)0.29

:

N

2

' '

6 7

F

'

o

u

n

d

:

Ν

'

2

Λ

5

'

(N-pyridinium)polystyrene tosylate, c h l o r i d e . C

H

C

H

C

H

4

9 9

1

0

,

4

m e q

a n d

t o l u e n

( 10 10)0.01'( 8 8)0.75( 10 12%.24 ( · 8» ) s u l f o n y l c h l o r i d e (5.0 g, 26 meq) were suspended i n d r y p y r i d i n e (60 ml, 700 meq) c h i l l e d i n an i c e b a t h t o 0°C under n i t r o g e n . The m i x t u r e was a l l o w e d t o warm t o room temperature over 4 hours, then r e f l u x e d f o r 2 h o u r s , then c o o l e d and f i l t e r e d , and t h e r e s i d u e washed 3 X H 0 , 1 X MEK, I X C H C 1 , 1 X CH3OH, 1 X E t 0 , and d r i e d under vacuum o v e r n i g h t , y i e l d i n g 6.72 g of a peach-coloured powder: IR (KBr) peaks absent a t 1046 cm" f o r a l c o h o l p r e c u r s o r , a t 1363 and 1176 cm" f o r t o s y l e s t e r i n t e r m e d i a t e , and a t 1245 and 657 f o r a l k y l c h l o r i d e s i d e - p r o d u c t ; peaks p r e s e n t a t 3500 ( s , b r , absorbed H 0 ) , 1633 (m, p y r ) , 1582 (w, p y r ) , 1196 ( s , S0-0"), 1123 ( s . S0-0"), 1034 ( s , S0-0"), 1012 ( s , S0-0"), 682 (m, p y r ) and 569 cm" (m, A r S 0 " ) . The product was then washed w i t h c o n c e n t r a t e d h y d r o c h l o r i c a c i d , then 1 X HC1/H 0:THF 1:1, 1 X HC1/H 0:THF 1:4, 3 X H 0 , 1 X MEK, 1 X C H C 1 , 1 X CH 0H, 1 X E t 0 , 1 X hexane, and d r i e d under vacuum 2

2

2

2

1

1

2

+

1

3

2

2

2

2

3

2

2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2.

33

Dimethyiene Spacers

DARLING A N D FRÉCHET

o v e r n i g h t , y i e l d i n g 5.99 g o f beige powder: IR (KBr) peaks absent a t 1196, 1123, 1034, 1012 and 569 cm" f o r t o s y l a t e a n i o n ; peaks s t i l l p r e s e n t a t 1633, 1582 and 682 cm" f o r p y r i d i n i u m n u c l e u s . Anal. 1

1

Calcd for ( C C I , 6.19.

1 0

H

)

1 0

C

0

0

H

C

H

l«( 8 8)o 7 5 ( 1 5 1 6

N C 1

) o 24

:C 1

6

» '

1 5

F

'

o

u

n

d

:

(N-pyrrolidinethyl)polystyrene. C

H

C

H

C

H

S 0

( 10 10)0.01-( 8 8)0.70-( 17 18 3)0.29 (Toluenesulfonyloxyethyl)p o l y s t y r e n e (0.19 g,*0.34 meq), d r y p y r r o l i d i n e (0.032 ml, 0.38 meq) and anhydrous p o t a s s i u m c a r b o n a t e (o.050 g, 0.36 meq) were s t i r r e d i n 2 ml d r y p y r i d i n e under n i t r o g e n a t room temperature f o r 2 h o u r s , then s l o w l y warmed t o r e f l u x over 5 h o u r s . The red-orange s u s p e n s i o n was f i l t e r e d , and t h e r e s i d u e washed 3 X H 0 , 1 X MEK, I X C H C 1 , 1 X E t 0 , and d r i e d under vacuum o v e r n i g h t t o g i v e a y e l l o w - b e i g e powder: IR (KBr) peaks absent a t 1363 and 1176 c m for tosic ester p r e c u r s o r , and a t 1633, 158 1123, 1034, 1012, 682 an t o s y l a t side-products pea p r e s e n t a t 2784 cm" ( C H ) . A n a l . C a l c d f o r 2

2

2

2

- 1

1

2

C

H

C

H

C

H

N

:Ν

3

( 1 0 1 0 ) 0 . 0 1 - ( 8 8 ) 0 . 7 0 - ( 1 4 1 9 ) 0.29 ' '

0 6

F

'

o

u

n

d

:

N

2

' '

9 8

'

(N-pyrrolidinonethyl)polystyrene. ( 10 10)0.01-( 8 9)0.794'( 17 18 3)0.196 (Toluenesulfonyloxyethyl)p o l y s t y r e n e (0.31 g, 0.42 meq), d r y p y r r o l i d i n o n e (0.051 ml, 0.66 meq) f r e s h l y - c r u s h e d potassium h y d r o x i d e (0.11 g, 2.0 meq) were r a p i d l y s t i r r e d i n 4 ml dry d i m e t h y l s u l f o x i d e under n i t r o g e n a t room temperature f o r 3 h o u r s , t h e n a t 60°C f o r 24 hours. The beige-brown s u s p e n s i o n was then f i l t e r e d , and t h e r e s i d u e washed 3 X H 0 , 1 X MEK, 1 X C H C 1 , 2 X CH3OH, and d r i e d under vacuum o v e r n i g h t , y i e l d i n g 0.26 g o f p a l e y e l l o w - b e i g e powder: IR (KBr) peaks absent a t 1363 and 1176 cm" f o r t o s i c e s t e r p r e c u r s o r ; peak p r e s e n t a t 1691 ( s , NC=0) cm" . A n a l . C a l c d f o r C

H

C

H

C

H

S 0

2

2

2

1

1

C

H

C

H

C

H

N

( 10 10)0.01-( 8 8)0.794-( 14 17 °)0.196

:

Ν

2

' -

1 8

'

F

o

u

n

d

:

N

2

' '

0 6

'

(3-nitrobenzoyloxyethyl)polystyrene. ( C

H

C

H

C

H

S 0

10 10)0.01-( 8 8)0.794'( 17 18 3)0.196 (Toluenesulfonyloxyethyl)p o l y s t y r e n e (0.41 g, 0.55 meq), n - n i t r o b e n z o i c a c i d p a l e grey powder (0.14 g, 0.83 meq) and anhydrous p o t a s s i u m c a r b o n a t e (0.17 g, 1.2 meq)were r a p i d l y s t i r r e d i n a m i x t u r e o f 4 ml d i m e t h y l s u l f o x i d e and 0.5 ml hexamethylphosphoramide under n i t r o g e n and warmed t o 60°C f o r 22 h o u r s . The p a l e brown s u s p e n s i o n was f i l t e r e d and washed 1 X a c e t o n e , 3 X H 0 ( r a p i d l y ) , 1 X MEK, I X C H C 1 , 1 X E t 0 , and d r i e d under vacuum o v e r n i g h t , y i e l d i n g 0.41 g of y e l l o w - b e i g e powder: IR (KBr) peaks absent a t 1363 and 1176 cm" f o r t o s i c e s t e r p r e c u r s o r , and a t 1046 cm" f o r h y d r o l y s i s s i d e - p r o d u c t ; peaks p r e s e n t a t 1727 ( s , C=0), 1535 ( s , A r - N 0 ) , 1351 ( s , N 0 ) , 1263 (m, C0-0), 1134 (Mm< C0-0) and 720 (m, Ar-H) cm" . A n a l . C a l c d f o r 2

2

2

2

1

1

2

2

1

C

H

C

H

C

H

N 0

( 10 10)0.01'( 8 8)0.794-( 17 15 4)0.196

:

N

l

' '

9 3

'

F

o

u

n

d

:

N

1

> '

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

8 7

'

34

CHEMICAL REACTIONS ON POLYMERS

ACKNOWLEDGMENTS F i n a n c i a l support of t h i s r e s e a r c h by the N a t u r a l S c i e n c e s and E n g i n e e r i n g R e s e a r c h C o u n c i l o f Canada i n the form o f an o p e r a t i n g g r a n t ( t o JMJF) and a p o s t - g r a d u a t e s c h o l a r s h i p ( t o GDD) i s g r a t e f u l l y acknowledged.

LITERATURE CITED 1. From Darling, G.D.; Ph.D. Dissertation, University of Ottawa, Ottawa, Ontario, Canada, 1987. 2. Pepper, K.W.; Paisley, H.M.; Young, M.A.; J. Chem. Soc., 1953, 4097. 3. Merrifield, R.B.; J. Am. Chem. Soc., 1963, 85, 2149. 4. Akelah, Α.; Sherrington, D.C.; Chem. Rev., 1981, 81, 557. Fréchet, J.M.J.; Tetrahedron, 1981, 37, 663. Hodge, P.; Sherrington D.C (Editors); "Polymer-Supported Reactions in Organi Mathur, N.K.; Narang Organic Chemistry", Academic Press, 1980. 5. Ford, W.T. (Editor); "Polymeric Reagents and Catalysts", American Chemical Society, Washington, D.C., 1986. 6. Pinnell, R.P.; Khune, G.D.; Khatri, N.A.; Manatt, S.L.; Tetrahedron Lett., 1984, 25, 3511. 7. Fréchet, J.M.J.; Polym. Sci. Tech., 1984, 24, 1. Fréchet, J.M.J.; De Smet, M.D.; Farrall, M.J.; J. Org. Chem., 1979, 44, 1774. 8. Arnett, E.M.; Reich, R.; J. Am. Chem. Soc., 1980, 102, 5892. 9. Westaway, K.C.; Poirier, R.A.; Can. J. Chem., 1975, 53, 3216. 10. Deady, L.W.; Korytsky, O.L.; Tetrahedron Lett., 1979, 451. 11. Dehmlow, E.V.; Slopianka, M.; Heider, J . ; Tetrahedron Lett., 1977, 2363. 12. Snyder, H.R.; Speck, J.C.; J. Am. Chem. Soc., 1939, 61, 2895. 13. Tomoi, M.; Ford, W.T.; J. Am. Chem. Soc., 1981, 103, 3821. 14. Cinorium, M.; Colonna, S.; Molinari, H.; Montanari, F.; J. Chem. Soc. (C), 1976, 394. 15. Traynelis, V.J.; Ode, R.H.; J. Org. Chem, 1970, 35, 2207. 16. Mariella, R.P.; Brown, K.H.; Can. J. Chem., 1973, 53, 2177. 17. Snyder, H.R.; Speck, J.C.; J. Am. Chem. Soc., 1939, 61, 668. 18. Vorbruggen, H.; Krolikiewicz, K.; Chem. Ber., 1984, 117, 1523. 19. Searles, S.; Nukina, S.; Chem. Rev., 1959, 59, 1077. 20. Barluenga, J . ; Alonso-Cires, L.; Campos, P.J.; Asensio, B.; Synthesis, 1983, 53. 21. Lecavalier, P.; Bald, E.; Jiang, Y.; Fréchet, J.M.J.; Hodge, P.; Reactive Polymers, 1985, 3, 315. 22. Colwell, A.R.; Duckwall, L.R.; Brooks, R.; McManus, S.P.; J. Org. Chem, 1981, 46, 3097. 23. Worster, P.M.; McArthur, C.R.; Leznoff, C.C.; Angew. Chem., Int. Ed. Engl., 1979, 18, 221. 24. Deady, L.W.; Korytsky, D.L.; J. Org. Chem., 1979, 45, 2717. 25. Patchornik, Α.; Kraus, M.A.; J. Am. Chem. Soc., 1970, 92, 7587. 26. Camps, F.; Castells, J . ; Ferrando, M.J.; Font, J . ; Tetrahedron Lett., 1971, 1713. 27. Goldfarb, Y.L.; Ispiryan, R.M.; Belenkii, L.I.; Dokl. Cheml Proc. Acad. Sci. USSR Chem. Sec., 1967, 209.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2.

DARLING A N DFRÊCHET

Dimethyiene Spacers

35

28. Gilman, H.; Brook, A.G.; Miller, L.S.; J. Am. Chem. Soc., 1953, 75, 4531. 29. Chan, T.H.; Chang, E.; Vinokur, E.; Tetrahedron Lett., 1970, 1137. 30. Hartung, W.H.; Simonoff, R.; Org. React., 1953, 7, 263. 31. Erhardt, P.W.; Synth. Commun., 1983, 13, 103. 32. Newhome, G.R.; Majestic, V.K.; Sauer, J.D.; Org. Prep. Proced. Int., 1980, 12, 345. 33. Tweedie, V.L.; Allabash, J.C.; J. Org. Chem., 1961, 26, 3676. 34. Oda, R.; Hayashi, Y.; Tetrahedron Lett., 1967, 3141. 35. Fréchet, J.M.J.; Eichler, E.; Polym. Bull., 1982, 7, 345. 36. Ford, W.T.; Ref. 5, 155. 37. Farrall, M.J.; Fréchet, J.M.J.; J. Org. Chem., 1976, 41, 3877. Frechet, J.M.J.; Farrall, M.J.; "Chemistry and Properties of Crosslinked Polymers" (Labana, S.S., Editor), Academic Press, 59, 1977. 38. Chambers, R.A.; Pearson D.E. J Org Chem. 1963 28 3144 39. March. J. "Advanced Interscience, Toronto, 40. Chan, T.H.; Fleming, I.; Synthesis, 1979, 761. 41. Neckers, D.C.; Ref. 5, 107. 42. Brown, J.M.; Jenkins, J.Α.; J. Chem. Soc., Chem Comm., 1976, 458. 43. Molinari. H.; Montanari, F.; Quici, S.; Tundo, P.; J. Am. Chem. Soc., 1979, 101, 3920. 44. Tomoi, M.; Ikeda, M.; Kakiuchi, H.; Tetrahedron Lett., 1978, 3757. 45. Fischer, O.; Chem. Ber., 1899, 32, 1297. 46. M.Kametami, C,; Nomura, Y.; Chem. Pharm. Bull., 1960, 8, 741. 47. Kametami, T.; Kigasawa, K.l Hiiragi, M.; Wagatsuna, N.; Wakisaka, K.; Tetrahedron Lett., 1969, 635. 48. Tiffeneau, M.; Fuhrer, K.; Bull. Soc. Chim. Fr., 1914, 15, 162; Chem. Abstr. 8, 1567. 49. Bosch, P.; Font, J . ; Moral, Α.; Sanchez-Ferrando, F.; Tetrahedron, 1978, 34, 947. 50. Lieto, J . ; Milstein, D.; Albright, R.L.; Minkiewicz, J.V.; Gates, B.C.; CHEMTECH, 1983, (1), 46. 51. Camps, F.; Castells, J . ; Pi, J . ; An. Quim., 1974, 70, 848; Chem. Abstr. 83, 10018g. 52. Chiles, M.S.; Jackson, D.D.; Reeves, P.C.; J. Org. Cheml, 1980, 45, 2915. 53. Tomoi, M.; Ogawa, E.; Hosokama, Y.; Kakiuchi, H. J. Polym. Sci., Polym. Chem. Ed., 1982, 20, 3015, 3421. 54. Farrall, M.J.; Alexis, M.; Trecarten, M.; Nouv. J. Chim., 1983, 7, 449. 55. Cristol, S.J.; Douglass, J.R.; Meek, J.S.; J. Am. Chem. Soc., 1951, 73, 816. 56. Lebedev, N.N.; Baranov, Y.I.; Vysokomolekul. Spedin., 1966, 8, 198; Chem. Abstr., 65, 808g. 57. Darling, G.D.; Fréchet, J.M.J.; J. Org. Chem., 1986, 51, 2270. 58. Hirao, Α.; Takenada, K.; Yamaguchi, K.; Nakahama, S.; Yamazaki, N.; Polym. Comm., 1983, 24, 339. 59. Tundo, P.; Synthesis, 1978, 315. 60. McManus, S.P.; Olinger, R.D.; J. Org. Chem., 1980, 45, 2717. 61. Tomoi, M.; Kori, N.; Kakiuchi, H.; Reactive Polymers, 1985, 3, 341.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

36

62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74. 75. 76. 77.

CHEMICAL REACTIONS ON POLYMERS

Whalley, W.B.; J. Chem. Soc., 1950, 2241. Lee, C.C.; Spinks, J.W.T.; J. Am. Chem. Soc., 1960, 82, 138. Saunders, W.H.; Edison, D.H.; J. Am. Chem. Soc., 1960, 82, 138. Veeravagu, P.; Arnold, R.T.; Eigenmann, E.W.; J. Am. Chem. Soc., 1964, 86, 3072. March, J . ; Ref. 39, 895. Cheminat, Α.; Benezra, C.; Farrall, M.J.; Fréchet, J.M.J.; Can. J. Chem., 1981, 59, 1405. Tipson, R.S.; J. Org. Chem., 1944, 9, 235. Nagasaka, T.; Ito, H.; Ozawa, N.; Kosugi, Y.; Hamaguchi, F.; Yakugaku Zasshi, 1980, 100, 962. Mukaiyama, T.; Angew. Chem. Int. Ed. Engl, 1979, 18, 707. Paquette, L.A.; Nelson, N.A.; J. Org. Chem., 1962, 27, 1085. Darling, G.D.; Bald, E.; Fréchet, J.M.J.; Polym. Prep., Am. Chem. Soc., Div. Polym. Chem., 1983, 24, 354. Sugasawa, S.; Akahoshi, S.Y.; Suzuki, M.; J. Pharm. Soc. Japan, 1952, 72, 1273; Chem Abstr. 1953 47 10539g Decker, H.; Chem. Ber. Liveris, M.; Miller, ; , , , Nishikubo, T.; Iizawa, T.; Ashi, K.K.; Okawara, M.; Tetrahedron Lett., 1981, 22, 3873. Oediger, H.; Moller, F.; Angew. Chem., Int. Ed. Engl., 1967, 6, 76.

RECEIVED August

27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 3

Chemical Modification of Poly(vinyl chloroformate) by Phenol Using Phase-Transfer Catalysis 1

S. Boivin, P. Hemery, and S. Boileau

College de France, 11 Place Marcelin Berthelot, 75231 Paris Cédex 05, France

The nucleophili formate) with pheno conditions has been studied. The C-NMR spectra of partly modified polymers have been examined in detail in the region of the tertiary carbon atoms of the main chain. The results have shown that the substitution reaction proceeds without degradation of the polymer and selectively with the chloroformate functions belonging to the different triads, isotactic sequences being the most reactive ones. 13

F u n c t i o n a l i z e d polymers have found i n c r e a s i n g use as s u p p o r t s , r e a g e n t s or c a t a l y s t s namely i n the f i e l d o f o r g a n i c s y n t h e s i s , m e t a l c h e l a t i o n o r pharmacology (J_). I t i s w e l l known t h a t c h e m i c a l m o d i f i c a t i o n o f polymers c o n t a i n i n g f u n c t i o n a l groups i s one o f t h e g e n e r a l r o u t e s f o r the s y n t h e s i s o f new p o l y m e r i c r e a g e n t s . I n the l a s t few y e a r s , the study o f the r e a c t i o n s o f the f u n c t i o n a l groups o f macromolecules has r e c e i v e d much a t t e n t i o n . K i n e t i c s and mechanisms of p o l y m e r - t r a n s f o r m a t i o n r e a c t i o n s depend on c h a r a c t e r i s t i c p o l y m e r i c e f f e c t s l i k e neighbouring-groups e f f e c t s as w e l l as c o n f i g u r a t i o n a l , c o n f o r m a t i o n a l , e l e c t r o s t a t i c o r super-molecular e f f e c t s . A t h e o r e t i c a l study s h o u l d take i n t o account a l l these e f f e c t s but i n p r a c t i c e the c o n s i d e r a t i o n o f even one o f them i s v e r y d i f f i c u l t . A mathematical treatment has been proposed by BOUCHER ( 2 ) and by PLATE and NOAH ( 3 ) . One o f t h e best known examples o f p o l y m e r - t r a n s f o r m a t i o n r e a c t i o n s i s the q u a t e r n i z a t i o n o f p o l y ( 4 - v i n y l p y r i d i n e ) by v a r i o u s a l k y l

Current address: Laboratoire de Chimie Macromoleculaire associe au Centre National de la Recherche Scientifique: U A 2 4 , Paris, France 0097-6156/88/0364-0037$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

38

and a r y l a l k y l h a l i d e s which y i e l d s a p o l y e l e c t r o l y t e . K i n e t i c s t u d i e s have been r e p o r t e d by s e v e r a l a u t h o r s ( 4 - 7 ) . They found r e t a r d a t i o n o f the r e a c t i o n which has been a t t r i b u t e d t o a dominant n e i g h b o u r i n g - g r o u p s e f f e c t w i t h t h e r e a c t i v i t y o f a p y r i d y l group m a i n l y due t o t h e s t e r i c h i n d r a n c e o f i t s m o d i f i e d n e i g h b o u r s . S i m i l a r n e i g h b o u r i n g - g r o u p s e f f e c t s as w e l l as e l e c t r o s t a t i c e f f e c t s have been observed i n the case o f n u c l e o p h i l i c s u b s t i t u t i o n o f p o l y ( m e t h y l m e t h a c r y l a t e ) w i t h o r g a n o l i t h i u m r e a g e n t s and t h e i r analogues ( 8 ) . Another well-known example o f p o l y m e r - t r a n s f o r m a t i o n r e a c t i o n i s the h y d r o l y s i s o f p o l y ( m e t h y l m e t h a c r y l a t e ) . K i n e t i c and m e c h a n i s t i c s t u d i e s c o r r e s p o n d i n g t o t h i s k i n d of r e a c t i o n have shown t h a t t h e r e a c t i v i t y o f e s t e r groups i s s e n s i t i v e t o r e a c t i o n c o n d i t i o n s , n e i g h b o u r i n g - g r o u p s e f f e c t s and t o polymer t a c t i c i t y ( 9 - 1 3 ) . Under b a s i c c o n d i t i o n s i t has been found t h a t s y n d i o t a c t i c sequences would be t h e most r e a c t i v e . Such c o n f i g u r a t i o n a l as w e l l as c o n f o r m a t i o n a l e f f e c t s have been a l s o r e p o r t e d by MILLAN t a l i th f nucleophili substitution of poly(viny and w i t h sodium i s o o c t y l t h i o g l y c o l a t ( 1 5 ) . The a u t h o r s have shown t h a t these r e a c t i o n s proceed s e l e c t i v e l y on t h e i s o t a c t i c TT d i a d s which can o n l y e x i s t e i t h e r i n t h e GTTG* i s o t a c t i c o r i n the TTTG h e t e r o t a c t i c t r i a d s , t h e former ones b e i n g much more r e a c t i v e than t h e l a t t e r ones. Nucleophilic substitution of chlorine i n poly(vinyl chloroformate) (PV0CC1) has been r e p o r t e d as one o f the b e s t procedure f o r the s y n t h e s i s o f new f u n c t i o n a l polymers (j_6). I t has been shown t h a t PV0CC1 can r e a c t w i t h n u c l e o p h i l i c compounds c o n t a i n i n g labile hydrogen atoms l i k e a l c o h o l s , phenols and amines (J_7). S i n c e i t i s p o s s i b l e t o prepare w e l l - d e f i n e d h i g h m o l e c u l a r weight PV0CC1 i n q u a n t i t a t i v e y i e l d s (J_8,J_9), c o n v e n i e n t c o n d i t i o n s have been found f o r the c h e m i c a l m o d i f i c a t i o n o f t h i s polymer w i t h e x c e l l e n t y i e l d s o f s u b s t i t u t i o n ( 2 0 ) . The b e s t r e s u l t s have been o b t a i n e d by u s i n g phase t r a n s f e r c a t a l y s i s (21-24). The u s e f u l n e s s o f t h i s t e c h n i q u e t o perform a g r e a t d e a l o f r e a c t i o n s i s now w e l l e s t a b l i s h e d i n o r g a n i c c h e m i s t r y (25-27). I n phase t r a n s f e r c a t a l y s i s a s u b s t r a t e i n an o r g a n i c phase i s r e a c t e d c h e m i c a l l y w i t h a reagent p r e s e n t i n another phase which i s u s u a l l y aqueous o r s o l i d . R e a c t i o n i s a c h i e v e d by means o f t h e t r a n s f e r agent; t h i s agent o r c a t a l y s t i s c a p a b l e o f s o l u b i l i z i n g o r e x t r a c t i n g i n o r g a n i c and o r g a n i c i o n s , i n the form o f i o n p a i r s , i n t o o r g a n i c media " (E.V. Dehmlow and S.S. Dehmlow ( 2 5 ) ) . I n the case o f the c h e m i c a l m o d i f i c a t i o n o f PV0CC1, two phases systems have been used : an o r g a n i c phase (PV0CC1 i n CH2CI2) and e i t h e r an aqueous phase (aq. 50% NaOH) o r a s o l i d phase (K2CO3 , potassium c a r b o x y l a t e ) w i t h a c a t a l y t i c amount o f BU4NHSO4 (TBAH), d i c y c l o h e x y l - l 8 - c r o w n - 6 o r c r y p t a n d [222]. These phase t r a n s f e r c a t a l y s i s c o n d i t i o n s a r e m i l d enough i n o r d e r t o a v o i d polymer d e g r a d a t i o n : they r e q u i r e l o w e r temperatures and s h o r t e r r e a c t i o n times than c l a s s i c a l c o n d i t i o n s . Furthermore, t h e a d d i t i o n o f a phase t r a n s f e r c a t a l y s t a l l o w s t o modify PV0CC1 w i t h a l k a l i n e s a l t s l i k e a l k a l i n e c a r b o x y l a t e s (22) o r w i t h u n s a t u r a t e d h e t e r o c y c l i c amines l i k e i n d o l e o r c a r b a z o l e (23,24). 11

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

3.

BOIVIN E T AL.

39

Phase-Transfer Catalysis

Moreover i t has been shown t h a t PV0CC1 prepared by f r e e - r a d i c a l p o l y m e r i z a t i o n o f v i n y l c h l o r o f o r m a t e (V0CC1) i s an a t a c t i c polymer h a v i n g a B e r n o u i l l i a n s t a t i s t i c a l d i s t r i b u t i o n as expected ( J j ) ) . I n o r d e r t o extend our s t u d i e s on t h e c h e m i c a l m o d i f i c a t i o n o f PV0CC1, the s t e r e o s e l e c t i v e c h a r a c t e r o f t h e n u c l e o p h i l i c s u b s t i t u t i o n o f the c h l o r o f o r m a t e u n i t s w i t h phenol has been examined by t h e s t u d y o f the 13c-NMR s p e c t r a o f p a r t l y m o d i f i e d polymers i n t h e r e g i o n o f t h e a l i p h a t i c methine carbon atoms. The r e s u l t s o b t a i n e d i n t h i s f i e l d a r e p r e s e n t e d here.

EXPERIMENTAL

Polymer p r e p a r a t i o n . PV0CC1 sample has been prepared by f r e e - r a d i c a l p o l y m e r i z a t i o n o f pure V0CC1 ( a c q u i r e d from t h e SNPE, p u r i t y 99%) i n CH Cl2 a t 35°C u s i n g d i c y c l o h e x y l p e r o x y d i c a r b o n a t initiator The e x p e r i m e n t a l procedur The m o l e c u l a r weight M 2

P r e p a r a t i o n o f m o d i f i e d polymers. P h e n o l , BU4NHSO4 (TBAR), C H C 1 a r e commercial p r o d u c t s and they a r e used w i t h o u t s p e c i a l p u r i f i c a t i o n . The method f o r t h e c h e m i c a l m o d i f i c a t i o n o f PV0CC1 w i t h phenol has been d e s c r i b e d elsewhere (20,21). The degrees o f s u b s t i t u t i o n have been determined by e l e m e n t a l a n a l y s i s o f t h e r e m a i n i n g CI and C c o n t e n t s and by H NMR a c c o r d i n g t o the i n t e g r a t i o n o f the d i f f e r e n t peaks observed. The ^H-NMR s p e c t r a have been r e c o r d e d a t 60 MHz i n CD3COCD3 a t 27°C : ô(ppm/TMS) : ^CHar. : 7.1 ppm; -CH c h a i n : 5.2 ppm; -CH ~ c h a i n : 2.1 ppm. * 2

2

1

(

2

1

3c-NMR s p e c t r o s c o p y . The t a c t i c i t i e s f o r both s t a r t i n g and m o d i f i e d polymers have been determined from t h e 3c-NMR s p e c t r a r e c o r d e d a t 50.3 MHz, a t 20°C, w i t h a AM 200 SY Bruker s p e c t r o m e t e r . The polymers have been examined as a 10$ s o l u t i o n i n CD3COCD3 ( r e f : TMS). 1

1

RESULTS AND DISCUSSION

In a p r e v i o u s work i t has been found t h a t t h e c h e m i c a l m o d i f i c a t i o n o f PV0CC1 by phenol i n CH2CI2, by u s i n g p y r i d i n e as HC1 scavenger, l e a d s to a s o l u b l e polymer c o n t a i n i n g 88% o f v i n y l p h e n y l carbonate u n i t s (20). A b e t t e r y i e l d o f s u b s t i t u t i o n has been o b t a i n e d by u s i n g a liquid/liquid two phases system (50% aqueous NaOH/CH2Cl2) w i t h BU4NHSO4 as phase t r a n s f e r c a t a l y s t (21_,24) a c c o r d i n g t o t h e f o l l o w i n g r e a c t i o n scheme :

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

40

CHEMICAL REACTIONS ON POLYMERS

aq. 50% NaOH 00 Na

+

~CH -CH~ + Ô 0=0 Ô A 0

NBu^ X

^_

00 NBu^

+

-HNBUj.^X

—

00 NBu,"

+ A,CH -CH-~ 2

2

ÇH Ç1 2

4

Na X

n

6

4

0=0 01

X" : C l " ; HS0 ~

2

4

Under such c o n d i t i o n s the s u b s t i t u t i o n r e a c t i o n o f PV0CC1 w i t h phenol i s q u i t e f a s t a t room temperature as shown by the r e s u l t s o f Table I . The degree o f s u b s t i t u t i o whereas the m o d i f i c a t i o c o n d i t i o n s (run 3 ) . Table I . Chemical m o d i f i c a t i o n o f PV0CC1 by phenol a t room temperature (PV0CC1 : 5 mmole; [Na0H]/[PV0CCl] = 2; [TBAH]/[PV0CC1] = 0.05)

Run

1 2 3 4 5 6 7

0OH (mmole)

CH C1 (ml)

5.1 5.0 5.1 5.1 0.7

50 50 50 50 35 40 45

1

2

4

'R 2.3

time (mn.)

2

15 25 45 120 20 35 30

^b) 84 91 100 98 14 29 46

a) D.S.(fl) -j-^c) 86

-

100 12 27 48

d

IH ^ _

-

100 14 29 44

a

^degree of s u b s t i t u t i o n b)determined by e l e m e n t a l a n a l y s i s o f the r e m a i n i n g C l and C. °)determined by H NMR. ) c a l c u l a t e d from the i n t e g r a t i o n o f the methine carbon peaks on 3c-NMR s p e c t r a . 1

d

1

R a t i o s [ c h l o r o f o r m a t e ] / [ p h e n o l ] h i g h e r than 1 have been used i n o r d e r t o prepare m o d i f i e d polymers w i t h a degree o f s u b s t i t u t i o n lower than 50% (runs 5-7, Table I ) . Under such c o n d i t i o n s i t can be n o t i c e d t h a t the s u b s t i t u t i o n r e a c t i o n s proceed q u a n t i t a t i v e l y w i t h r e s p e c t t o the i n i t i a l phenol c o n t e n t . The e v o l u t i o n o f the 3rj-NMR s p e c t r a o f m o d i f i e d polymers w i t h the degree o f s u b s t i t u t i o n , i n the r e g i o n o f the a l i p h a t i c methine carbon atoms, i s shown i n F i g u r e 1. Spectrum A c o r r e s p o n d i n g t o PV0CC1 p r e s e n t s t h r e e s i g n a l s l o c a t e d a t 78.9, 77.85 and 76.9 ppm which belong t o t e r t i a r y carbon atoms b e a r i n g c h l o r o f o r m a t e groups whereas the t h r e e s i g n a l s l o c a t e d a t 75.3, 73.6 and 72.0 ppm belong t o 1

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

BOIVIN ET AL.

Phase-Transfer Catalysis

F i g u r e 1. C-NMR s p e c t r a o f m o d i f i e d PV0CC1 samples a t v a r i o u s c o n v e r s i o n s : A ( 0 ? ) ; Β ( 1 4 % ) ; C ( 2 9 ? ) ; D ( 4 6 ? ) ; Ε (100?).

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

42

CHEMICAL REACTIONS ON POLYMERS

t e r t i a r y carbon atoms b e a r i n g carbonate groups. S p e c t r a B, C and D have been o b t a i n e d from p a r t l y m o d i f i e d polymers w i t h degrees o f s u b s t i t u t i o n e q u a l t o 14?, 29? and 46? r e s p e c t i v e l y (runs 5-7, Table I ) . I n the cases o f PV0CC1 and p o l y ( v i n y l phenyl carbonate) ( s p e c t r a A and Ε r e s p e c t i v e l y ) , t h e t e r t i a r y carbons o f t h e main c h a i n a r e s e n s i t i v e to t r i a d effects according to a B e r n o u i l l i a n s t a t i s t i c a l d i s t r i b u t i o n . Moreover, i n t h e case o f PV0CC1 (spectrum A ) , t h e m u l t i p l i c i t y o f t h e s i g n a l s shows t h a t t h e t e r t i a r y carbons o f t h e main c h a i n are l i k e l y s e n s i t i v e t o pentad e f f e c t s . The assignment o f the t h r e e main s i g n a l s t o i s o - , h e t e r o - and s y n d i o t a c t i c t r i a d s has been suggested p r e v i o u s l y f o r both PV0CC1 and p o l y ( v i n y l p h e n y l carbonate) ( 3 ) . I n t h e p r e s e n t work t h i s assignment has been c o n s i d e r e d t o be t r u e and i s i n d i c a t e d i n F i g u r e 1. I n t h e case o f p a r t l y m o d i f i e d polymers t h e s p e c t r a B, C and D show more c o m p l i c a t e d s t r u c t u r e s which can be presumably due t o s i g n i f i c a n t neighbouring-group groups and m o d i f i e d o r u n m o d i f i e methine carbon atoms. As shown i n Table I (runs 4-7) t h e degrees o f s u b s t i t u t i o n c a l c u l a t e d from the i n t e g r a t i o n o f t h e s i g n a l s c o r r e s p o n d i n g t o t h e methine carbons o f v i n y l c h l o r o f o r m a t e u n i t s and o f v i n y l phenyl carbonate u n i t s i n the m o d i f i e d polymers a r e i n good agreement w i t h the v a l u e s o b t a i n e d by e l e m e n t a l a n a l y s i s as w e l l as by 'H NMR. Such a r e s u l t a l l o w s t o compare the i n t e g r a t i o n s o f 3c-NMR s p e c t r a o f t h e s e polymers i n t h e r e g i o n o f t h e t e r t i a r y carbons o f t h e main c h a i n . The percentages o f t h e d i f f e r e n t t r i a d s b e a r i n g e i t h e r a c h l o r o f o r ­ mate o r a carbonate f u n c t i o n are r e p o r t e d i n Table I I . They have been c a l c u l a t e d from the i n t e g r a t i o n o f 3c-NMR s p e c t r a shown i n F i g u r e 1 . The sums o f the percentages ( i + i ' ) , (h+h') and ( s + s ) a r e independent o f the degree o f s u b s t i t u t i o n and a r e e q u a l t o t h e v a l u e s o f PV0CC1 ( i ) , ( h ) , ( s ) r e s p e c t i v e l y , w i t h i n the experimental e r r o r s . From these r e s u l t s i t i s r e a s o n a b l e t o c o n c l u d e t h a t no i n v e r s i o n i n the o r d e r o f the c h e m i c a l s h i f t s o f the t e r t i a r y carbon atoms b e l o n g i n g t o t h e d i f f e r e n t t r i a d s o c c u r s from t h e s t a r t i n g PV0CC1 t o t h e p o l y ( v i n y l phenyl c a r b o n a t e ) . Moreover t h e c h e m i c a l m o d i f i c a t i o n o f PV0CC1 by phenol does n o t induce any d e g r a d a t i o n o f the polymer. The degrees o f s u b s t i t u t i o n o f c h l o r o f o r m a t e f u n c t i o n s b e l o n g i n g t o i s o - , h e t e r o - and s y n d i o t a c t i c t r i a d s r e s p e c t i v e l y have been c a l c u l a t e d from t h e percentages shown i n Table I I . T h e i r e v o l u t i o n w i t h the t o t a l degree o f s u b s t i t u t i o n i s p l o t t e d i n F i g u r e 2. I t can be concluded t h a t t h e r e a c t i v i t y o f t h e c h l o r o f o r m a t e f u n c t i o n s decreases i n t h e f o l l o w i n g o r d e r : 1

1

f

i s o > hetero > syndio i n the f i r s t s t e p s o f s u b s t i t u t i o n (D.S. ^ 25?) . From the f o r e g o i n g i t c a n be suggested t h a t t h e c h l o r o f o r m a t e f u n c t i o n s b e l o n g i n g t o meso d i a d s are more r e a c t i v e than those b e l o n g i n g t o racemic d i a d s . A s i m i l a r r e s u l t has been observed p r e v i o u s l y by MILLAN e t a l . (J_4) i n the case o f t h e n u c l e o p h i l i c s u b s t i t u t i o n o f p o l y ( v i n y l c h l o r i d e ) w i t h sodium t h i o p h e n a t e .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

BOIVIN ET AL.

Phase- Transfer Catalysis

F i g u r e 2. Conversion o f c h l o r o f o r m a t e f u n c t i o n s c o r r e s p o n d i n g t o d i f f e r e n t t r i a d s ( i , h , s ) vs the degree o f s u b s t i t u t i o n o f the polymer.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

44

CHEMICAL REACTIONS ON POLYMERS

Table I I .

Percentages of i s o - , hetero- and syndiotactic triads bearing either a chloroformate or a carbonate group i n PV0CC1 and i n the modified polymers ) a

H-C-0C0C1 Run

b)

spectrum

(A) (B) (C) (D) (E)

PV0CC1 5 6 7 4 a

f

c)

6(ppm)

d)

78.9 i 0.25 0.19 0.16 0.11

H-Ç-OCO 0 2

77.85 h

76.9 s

75.3 i

73.6 h»

72.0 s

0.,48 0..41 0..34 0.,28

0..27 0..25 0..21 0..18

0 0.06 0.11 0.13

0 0.06 0.12 0.21

0 0.,02 0.,06 0., 10

f

1

f

) i+h+s+i +h +s'=1 ) see Table I. °)see F i g . 1. )Chemical s h i f t s of ~X-NMR signals corresponding to the a l i p h a t i c methine carbons of the main chain i n ppm/TMS. b

d

CONCLUSION

In conclusion the nucleophilic substitution of poly(vinyl chloroformate) with phenol by using a l i q u i d / l i q u i d two phases system (50% aqueous NaOH/CI^C^) with BU4NHSO4 as phase transfer catalyst proceeds both without degradation of the polymer and s e l e c t i v e l y with different triads. In order to explain why the chloroformate functions belonging to i s o t a c t i c sequences are the most reactive, further work i s presently undertaken concerning the study of the conformational structure of PV0CC1 macromolecules i n solution. Along the same l i n e , i t would be interesting to examine some substitution reactions of trimeric models having different stereoconfigurations. Moreover i t would be worth extending this preliminary study to the examination of the behaviour of PV0CC1 samples with different t a c t i c i t i e s .

REFERENCES 1. MATHUR,N.K.; NARANG,C.K.; WILLIAMS,R.Ε. Polymers as Aids in Organic Chemistry; Academic Press : New York, 1980; GECKELER,K.; PILLAI,V.N.R.; MUTTER,M. Adv. Polym. Sci. 1981, 39, 65; AKELAH,A.; SHERRINGTON,D.C. Chem. Rev. 1981, 81, 557; Polymer 1983, 24, 1369; FORD,W.T.; TOMOI,M. Adv. Polym. Sci. 1984, 55, 49. 2. BOUCHER,E.A. Prog. Polym. Sci. 1978, 6, 63. 3. PLATE,Ν.Α.; NOAH,O.V. Adv. Polym. Sci. 1979, 31, 133.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

3.

BOIVIN E T AL.

Phase-Transfer Catalysis

45

4. TSUCHIDA,E.; IRIE,S. J. Polym. Sci. Polym. Chem. Ed. 1973, 11, 789. 5. ΝΟΑΗ,Ο.V.; LITMANOVICH,A.D.; PLATE,N.A. J. Polym. Sci. Polym. Phys. Ed. 1974, 12, 1711. 6. MORCELLET-SAUVAGE,J.; LOUCHEUX,C. Makromol. Chem. 1975, 176, 315. 7. BOUCHER,E.A.; MOLLETT,C.C. J. Chem. Soc. Faraday Trans.1 1982, 78, 75; BOUCHER,E.A.; KHOSRAVIBABADI, E. J. Chem. Soc. Faraday Trans. 1 1983, 79, 1951. 8. BOURGUIGNON,J.J.; GALIN,J.J.; BELLISSENT,H.; GALIN,J.C. Polymer 1977, 18, 937; BOURGUIGNON,J.J.; GALIN,J.C. Polymer 1982, 23, 1493. 9. PLATE,N.A. Pure Appl. Chem. 1976, 46, 49. 10. DE LOECKER,W.; SMETS,G. J. Polym. Sci. 1959, 40, 203. 11. BAINES,F.C.; BEVINGTON,J.C. J. Polym. Sci. A-1 1968, 6, 2433. 12. KLESPER,E.; BARTH,V. Polymer 1976, 17, 777, 787. 13. BUGNER, D.E. Am. Chem Soc Polym Prep 1986 27(2) 57 14. MARTINEZ,G.; MIJANGOS,C. A-17, 1129; Polym Chem. Ed. 1985, 23, 1077; MIJANGOS,C.; MARTINEZ,G.; MICHEL,Α.; MILLAN,J.; GUYOT,A. Eur. Polym. J. 1984, 20, 1. 15. MIJANGOS,C.; MARTINEZ,G.; MILLAN,J. Eur. Polym. J. 1986, 22, 423. 16. MEUNIER,G.; BOIVIN,S.; HEMERY,P.; SENET,J-P.; BOILEAU,S. in Modification of Polymers; CARRAHER,C.E.; MOORE,J.A. Plenum Press : New York, 1983; Vol.21, p.2293. 17. SCHAEFGEN,J.R. Am. Chem. Soc. Polym. Prep. 1967, 8(1), 723; J. Polym. Sci. 1968, C24, 75. 18. BOILEAU,S.; JOURNEAU,S.; MEUNIER,G. Fr. Patent 1980, 2 475 558. 19. MEUNIER,G.; HEMERY,P.; BOILEAU,S.; SENET,J-P.; CHERADAME,H. Polymer 1982, 23, 849. 20. MEUNIER,G.; BOIVIN,S.; HEMERY,P.; BOILEAU,S.; SENET,J-P. Polymer 1982, 23, 861. 21. BOIVIN,S.; CHETT0UF,A.; HEMERY,P.; BOILEAU,S. Polym. Bull. 1983, 9, 114. 22. BOIVIN,S.; HEMERY,P.; SENET,J-P.; BOILEAU,S. Bull. Soc. Chim. France 1984, II 201. 23. KASSIR,F.; BOIVIN,S.; BOILEAU,S.; CHERADAME,H.; WOODEN,G.P.; OLOFSON,R.A. Polymer 1985, 26, 443. 24. BOIVIN,S.; HEMERY,P.; BOILEAU,S. Can. J. Chem. 1985, 63, 1337. 25. WEBER,W.P.; GOKEL,G.W. Phase Transfer Catalysis in Organic Synthesis, Springer-Verlag : New York, 1978; STARKS,C.M.; LIOTTA,C. Phase Transfer Catalysis : Principles and Techniques, Academic Press : New York, 1978; DEHMLOW,E.V.; DEHMLOW,S.S. Phase Transfer Catalysis, Verlag Chemie : Weinheim, 1980. 26. ANTOINE, J.P.; DE AGUIRRE, I.; JANSSENS, F.; THYRION, F. Bull. Soc. Chim. France 1980, 5-6, II-207. 27. MONTANARI, F.; LANDINI, D.; ROLLA, F. Topics in Current Chemistry 1982, 101, 147. RECEIVED August 27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter

4

Chemical Modification of Poly(2,6-dimethyl-1,4-phenylene oxide) and Properties of the Resulting Polymers Simona Percec and George Li Standard Oil Research and Development, 4440 Warrensville Center Road, Cleveland, OH 44128

The chemical modificatio f pol (2,6-dimethyl-1,4 phenylene oxide) (PPO reactions is presented was accomplished by the electrophilic substitution reactions such as: bromination, sulfonylation and acylation. The permeability to gases of the PPO and of the resulting modified polymers is discussed. Very good permeation properties to gases, better than for PPO were obtained for the modified structures. The thermal behavior of the substituted polymers resembled more or less the properties of the parent polymer while their solution behavior exhibited considerable differences. A l t h o u g h t h e use o f polymers as membrane m a t e r i a l s has i n c r e a s e d m a r k e d l y (1-3), t h e development o f s t r u c t u r e / p e r m e a b i l i t y r e l a t i o n s h i p has l a g g e d and i s an i m p o r t a n t a r e a o f f u t u r e investigations. Among t h e many a r o m a t i c polymers which p o s s e s s h i g h g l a s s t r a n s i t i o n t e m p e r a t u r e s , PPO (T =212*C) shows t h e h i g h e s t p e r m e a b i l i t y t o gases. One s i g n i f i c a n t f a c t o r i n i t s h i g h p e r m e a b i l i t y stems from l a r g e d i f f u s i o n c o e f f i c i e n t s o f gases i n PPO as compared t o o t h e r g l a s s y polymers w i t h r i g i d c h a i n backbone (4.) . In s p i t e o f t h i s , t h e r e l a t i v e l y low s e l e c t i v i t y t o gases a s s o c i a t e d w i t h t h e l a c k o f s o l u b i l i t y i n c o n v e n t i o n a l membrane forming d i p o l a r a p r o t i c solvents prevented the f a c i l e preparation of PPO membrane systems f o r a c t u a l use i n gas s e p a r a t i o n s . S e v e r a l s t u d i e s have a p p e a r e d i n t h e l i t e r a t u r e (5-9) d e s c r i b i n g t h e r e a c t i o n s o f v a r i o u s compounds w i t h PPO i n o r d e r t o change t h e p r o p e r t i e s o f t h i s polymer b u t none o f them have v a l u e d t h e c h e m i c a l s t r u c t u r e i n terms o f gas p e r m s e l e c t i v i t y b e h a v i o r . In o u r r e s e a r c h , t h r e e c h e m i c a l m o d i f i c a t i o n approaches were i n v e s t i g a t e d : bromination, s u l f o n y l a t i o n , and a c y l a t i o n on t h e a r o m a t i c r i n g . The s p e c i f i c o b j e c t i v e o f t h i s p a p e r i s t o p r e s e n t t h e c h e m i c a l m o d i f i c a t i o n on t h e PPO backbone by a v a r i e t y o f e l e c t r o p h i l i c s u b s t i t u t i o n r e a c t i o n s and t o examine t h e f e a t u r e s t h a t d i s t i n g u i s h m o d i f i e d PPO from u n m o d i f i e d PPO w i t h r e s p e c t t o gas p e r m e a t i o n p r o p e r t i e s , polymer s o l u b i l i t y and t h e r m a l b e h a v i o r . G

0097-6156/88/0364-0046$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

4. PERCEC AND LI

Poly(g,6-dimethyl-l,4-phenylene

oxide)

47

Experimental Materials.. The s t a r t i n g PPO was purchased from A l d r i c h Chemical Co. Two r e p r e c i p i t a t i o n s from chloroform into methanol served to p u r i f y the polymer. The bromine, chlorosulfonic acid, s u l f o n y l chlorides, a c i d chlorides as well as a l l other reagents and solvents were purchased from A l d r i c h Chemical Co. and were used without further purification. Aluminum t r i c h l o r i d e was sublimated i n a Pyrex glass tube p r i o r to use. Reactions. The bromination of the aromatic r i n g was achieved at room temperature using a known procedure . The sulfonylation reaction was performed i n a two-step process. The f i r s t step involved the reaction of PPO with chlorosulfonic acid according to a l i t e r a t u r e method (11). The sulfonated PPO was hygroscopic and unstable. We succeeded (12.) i n converting the sulfonate groups into stabl aromatic compounds at elevate solution was washed with d i l u t e sodium bicarbonate, and the product p r e c i p i t a t e d i n methanol, f i l t e r e d and dried. The F r i e d e l - C r a f t s substitution reactions (.13.) were c a r r i e d out i n nitrobenzene solution i n the presence of A1C1 , under nitrogen and a temperature range of 40-80 C. Sulfonyl chlorides (R S0 C1) and carboxylic a c i d chlorides (R C(0)C1) respectively, were used as s u l f o n y l a t i n g and acylating agents. After the required reaction time, the reaction mixture was washed with water u n t i l the pH was neutral. The separated polymer solution was dried over anhydrous MgS04, f i l t e r e d and p r e c i p i t a t e d i n methanol. A f i n a l p u r i f i c a t i o n was c a r r i e d out by p r e c i p i t a t i o n of the product from chloroform solution into methanol. The polymer was then vacuum dried to constant weight. The polymer films were prepared by d i s s o l v i n g the polymer i n a suitable solvent (chloroform) to form 7 wt% solutions. The solution was then poured over a clean glass plate and spread out evenly to a uniform thickness with the a i d of a doctor blade. The films were a i r dried, removed from the glass plate and further vacuum dried at 60 C for 72 hours. 3

e

1

2

2

e

Measurements. 200 MHz !H NMR spectra were recorded from CDC1 solu­ tions (TMS i n t e r n a l standard) on a Nicolet NT 200 spectrometer. DSC measurements were c a r r i e d out with a DuPont D i f f e r e n t i a l Scanning Calorimeter (Model 1090) under nitrogen atmosphere. The scanning rate was 10*C/min. i n a l l cases. Indium was used as a standard. Elemental analyses were performed by Standard O i l Research and Development A n a l y t i c a l Laboratory. A modified G i l b e r t c e l l (14.) was used to determine the gas permeation properties of polymer f i l m s . The t e s t i n g area of the f i l m was 45.8 cm . The f i l m thickness was i n a range of 1.27 χ 10~ mm - 2.81 χ 10~ mm. The test side was exposed to a carbon dioxide : methane : nitrogen mixture i n a mole r a t i o 3.11 : 33.6 : 63.29. The permeant was picked up by a c a r r i e r gas, helium, and injected i n t e r m i t t e n t l y through a sample valve into a gas chromâtograph for analysis. The p a r t i a l pressure of the test gas was 29.7 p s i (0.21 MPa) while the p a r t i a l pressure of the product gas on the permeant side was held at an i n s i g n i f i c a n t l e v e l by purging with 2 9.7 p s i 3

2

2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2

48

CHEMICAL REACTIONS ON POLYMERS

(0.21 MPa) h e l i u m a t a f l o w r a t e much i n e x c e s s rate.

of the permeation

R e s u l t s and D i s c u s s i o n B r o m i n a t e d PPO. The e l e c t r o p h i l i c a r o m a t i c b r o m i n a t i o n o f t h e PPO was c a r r i e d out i n c h l o r o f o r m s o l u t i o n t o y i e l d p o l y m e r s w i t h d i f f e r e n t degrees of s u b s t i t u t i o n . F o r the h i g h l y brominated s t r u c t u r e s t h e T expanded o v e r a c o n s i d e r a b l e t e m p e r a t u r e range. A maximum v a l u e o f 273'C was o b t a i n e d f o r 100 mol % b r o m i n a t e d PPO. The s o l u t i o n p r o p e r t i e s o f t h e b r o m i n a t e d PPO d e r i v a t i v e s were s i m i l a r t o t h o s e o f t h e p a r e n t polymer. The gas p e r m e a t i o n p r o p e r t i e s o f PPO and PPO c o n t a i n i n g between 6.5% t o 100% Br groups p e r r e p e a t u n i t a r e summarized i n T a b l e I . G

The s t e a d y s t a t e s e p a r a t i o n f a c t o r (a) f o r t h e two gases (C0 and CH ) i s d e f i n e d as t h e r a t i o o f t h e i r i n d i v i d u a l p e r m e a b i l i t i e s . The gas p e r m e a b i l i t y c o n s t a n t s (P) a r e g e n e r a l l y e x p r e s s e d by t h e amount o f t h e gas a t s t a n d a r f o r t h e t h i c k n e s s , membran gas as i n t h e f o l l o w i n g e q u a t i o n : 2

4

ρ

(Amount o f t h e gas) (Membrane t h i c k n e s s ) =

(Membrane area)

(Time)

( D i f f e r e n t i a l p r e s s u r e o f gas) 3

2

le

where Ρ i s e x p r e s s e d i n u n i t s cm (STP) c m » c m ~ » s ~ c m H g . P e r m e a b i l i t y i s a l s o as r e p o r t e d i n B a r r i e r , one B a r r i e r b e i n g e q u a l t o 1X10~ P. I t c a n be seen from T a b l e I t h a t no change e i t h e r i n p e r m e a b i l i t y f o r C 0 o r C0 /CH s e l e c t i v i t y was o b t a i n e d when t h e d e g r e e o f b r o m i n a t i o n f o r PPO i s low (6.5 m o l e % ) . However, a t h i g h e r l e v e l s o f b r o m i n a t i o n , t h e r e were i n c r e a s e s i n b o t h p e r m e a b i l i t y f o r C 0 and C0 /CH s e l e c t i v i t y . The maximum e f f e c t s (an i n c r e a s e o f 2.47 t i m e s f o r C 0 p e r m e a b i l i t y and 1.45 t i m e s f o r C0 /CH s e l e c t i v i t y t o t h a t o f PPO) were r e a c h e d a t 100% s u b s t i t u t i o n degree o f the aromatic r i n g . 10

2

2

2

4

2

4

2

2

4

S u l f o n y l a t e d PPO. The s u l f o n y l a t i o n i s a c h i e v e d by s u l f o n a t i o n r e a c t i o n on PPO, f o l l o w e d by t h e r e a c t i o n w i t h a r o m a t i c compounds as o u t l i n e d i n Scheme 1. No comments r e g a r d i n g t h e t h e r m a l and s o l u t i o n b e h a v i o r o f t h e p o l y m e r s o b t a i n e d by t h i s two s t e p p r o c e d u r e a r e i n c l u d e d here s i n c e t h e s e p r o p e r t i e s a r e d i s c u s s e d i n t h e next s e c t i o n f o r s u l f o n y l a t e d PPO m o d i f i e d under F r i e d e l - C r a f t s c o n d i t i o n s . The changes o f t h e C 0 p e r m e a b i l i t y and s e p a r a t i o n f a c t o r f o r C0 /CH , compared t o t h e t y p i c a l v a l u e s o f PPO s t a n d a r d a r e shown i n T a b l e I I f o r PPO m o d i f i e d w i t h d i f f e r e n t s u l f o n y l g r o u p s . The b e s t enhancement was o b t a i n e d f o r PPO c o n t a i n i n g p h e n y l s u l f o n e g r o u p s . The p r e s e n c e o f -S0 (OH) groups r e d u c e d t h e c a r b o n d i o x i d e p e r m e a b i l i t y by a f a c t o r o f t h r e e . T h i s can be e x p l a i n e d (JU5.) by t h e d e c r e a s e i n l o c a l segmental m o b i l i t y o f t h e polymer c h a i n s due t o t h e i n t e r a c t i o n s a r i s i n g from hydrogen b o n d i n g . However, t h e o v e r a l l t r a n s p o r t p r o c e s s f o r t h i s polymer membrane i s more c o m p l i c a t e d and i n v o l v e s a more pronounced d i s c r i m i n a t i o n a g a i n s t methane m o l e c u l e s due t o t h e h i g h l y p o l a r n a t u r e o f t h e polymer. T h i s l e a d s t o a t w o f o l d i n c r e a s e i n t h e C0 /CH s e p a r a t i o n f a c t o r . 2

2

4

2

2

4

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

4.

PERCEC AND LI

Table I .

No.

Poly(2,6'dimethyl-l,4-phenylene

The P e r m e a b i l i t y

Polymer

Substitution

49

oxide)

t o Gases o f B r o m i n a t e d PPO

*co

3

Degree )

«002/^4

2

b

(mol%)

(barrer) >

1.

PPO

0.0

64.00

16.40

2.

BRPPO

6.5

64.00

16.72

3.

BRPPO

21.5

67.20

17.71

4.

BRPPO

46.0

78.08

19.35

5.

BRPPO

6.

BRPPO

100.0

158.08

23.73

a)

Determined by elemental

b)

1 Barrer = 10"

10

analysis

[cm (STP) cm] / [cm «sec •cmHg] 3

2

α = Separation f a c t o r

SO,

CH

3

"

Ar Scheme 1. on PPO.

Two s t e p p r o c e d u r e o f s u l f o n y l a t i o n

reaction

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

50

CHEMICAL REACTIONS ON POLYMERS

Table I I .

The P e r m e a b i l i t y

t o Gases o f S u l f o n y l a t e d

No.

R

Substitution Degree

1.

Η

0

2.

3.

Ο - S - C H CH 6

4

3

- S - C H (CH ) O 6

3

4.

Ο - S - C H

5.

-

6.

- S - OH 6

6

3

5

S - C H C H Ο 6

2

4

2

5

D e t e r m i n e d by e l e m e n t a l

a )

P

C0

a 2

64

PPO

C0 /CH 2

4

16.4

60

89.60

21.81

23

72.96

20.00

38

99.20

27.38

31

73.60

16.40

—

19.84

32.80

analysis.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

4. P E R C E C A N D LI

Poly(2,6-dimethyl-l,4-phenylene oxide)

51

F r i e d e l - C r a f t s R e a c t i o n s on PPO and P r o p e r t i e s o f t h e R e s u l t i n g Polymers. There a r e two hydrogens on t h e a r o m a t i c r i n g o f PPO which can r e a c t t h r o u g h F r i e d e l - C r a f t s r e a c t i o n s . The s u b s t i t u t i o n o f t h e f i r s t a v a i l a b l e p o s i t i o n from t h e a r o m a t i c r i n g o c c u r s e a s i l y by t h e t r e a t m e n t o f t h e PPO w i t h s u l f o n y l c h l o r i d e o r a c i d c h l o r i d e s i n t h e presence of a F r i e d e l - C r a f t s c a t a l y s t . The r e m a i n i n g a r o m a t i c hydrogen c o u l d n o t be removed by a second a b s t r a c t i o n r e a c t i o n , and c o n s e q u e n t l y o n l y m o n o s u b s t i t u t i o n was a c h i e v e d . Table I I I p r e s e n t s t h e experimental r e a c t i o n c o n d i t i o n s used i n t h e s u l f o n y l a t i o n and a c y l a t i o n o f t h e PPO backbone and t h e degrees of s u b s t i t u t i o n obtained. The s u b s t i t u t i o n degree d e t e r m i n e d by H NMR s p e c t r o s c o p y was between 17.5% and 7 9 . 4 % , depending on t h e r e a c t i o n c o n d i t i o n s and s u l f o n y l a t i n g o r a c y l a t i n g agent. A complete s u b s t i t u t i o n o f t h e PPO a r o m a t i c r i n g s was n o t o b t a i n e d under t h e s e e x p e r i m e n t a l conditions. The p r e s e n c e o f one c a r b o n y l o r s u l f o n y l group a t t a c h e d t o a PPO p h e n y l r i n g , d r a s t i c a l l y d e c r e a s e s t h e n u c l e o p h i l i c i t y o f the remaining u n s u b s t i t u t e d i s u b s t i t u t i o n of the phenyleni t h e s t r o n g e l e c t r o n w i t h d r a w i n g c h a r a c t e r o f t h e c a r b o n y l and s u l f o n y l groups. A t t h e same time, when b u l k y s u b s t i t u e n t s a r e a t t a c h e d t o t h e PPO backbone, s t e r i c h i n d r a n c e a l s o d e c r e a s e s t h e a c c e s s a b i l i t y o f nearby u n s u b s t i t u t e d p o s i t i o n s (JL£) . Consequently, e l e c t r o n i c f a c t o r s r e t a r d t h e second e l e c t r o p h i l i c s u b s t i t u t i o n on t h e same PPO p h e n y l r i n g w h i l e s t e r i c f a c t o r s a l s o c o n t r i b u t e t o l i m i t t h e degree o f m o n o s u b s t i t u t i o n t o about 80%. T y p i c a l ^-H NMR s p e c t r a o f t h e s u l f o n y l a t e d PPO and a c y l a t e d PPO a r e p r e s e n t e d i n F i g u r e s 1-2 t o g e t h e r w i t h t h e assignment o f t h e i r p r o t o n i c r e s o n a n c e s (JJ7) . M u l t i p l e resonances from t h e a l i p h a t i c r e g i o n i n F i g u r e 1 a r e due t o t h e sequence d i s t r i b u t i o n o f t h e structural units. I t i s d i f f i c u l t t o p r o v i d e an e x a c t assignment f o r t h i s region at t h i s time. The p e r c e n t o f s u b s t i t u t i o n o f t h e PPO a r o m a t i c u n i t s was d e t e r m i n e d from t h e r a t i o o f t h e i n t e g r a l s o f p r o t o n r e s o n a n c e s due t o u n s u b s t i t u t e d 2 , 6 - d i m e t h y l - l , 4 - p h e n y l e n e u n i t s ( s i g n a l H a t 5=6.5 ppm) and s u b s t i t u t e d u n i t s ( s i g n a l at δ = 6 . 0 ppm). 1

a

In a l l c a s e s m o n o s u b s t i t u t i o n was demonstrated by m e a s u r i n g t h e r a t i o between t h e i n t e g r a l s o f t h e u n s u b s t i t u t e d a r o m a t i c p r o t o n o f t h e s u b s t i t u t e d p h e n y l e n i c u n i t s and some r e p r e s e n t a t i v e p r o t o n s from t h e newly a t t a c h e d pendant groups. F o r example, t h e r a t i o between t h e s i g n a l s c and e from s p e c t r a I I and I I I ( F i g u r e 1 ) , t h e r a t i o between t h e s i g n a l s c and f from t h e s p e c t r a IV and VI ( F i g u r e 2 ) , and c and e from t h e s p e c t r a VI ( F i g u r e 2) were u s e d t o demonstrate m o n o s u b s t i t u t i o n . Both t h e r m o g r a v i m e t r i c a n a l y s i s and d i f f e r e n t i a l s c a n n i n g c a l o r i m e t r i c s t u d i e s were c a r r i e d out on m o d i f i e d and u n m o d i f i e d PPO samples. T a b l e IV p r e s e n t s t h e weight l o s s e s and t h e g l a s s t r a n s i t i o n t e m p e r a t u r e s o f t h e most r e p r e s e n t a t i v e p o l y m e r s . As was e x p e c t e d , t h e s u b s t i t u t i o n o f PPO w i t h r i g i d and b u l k y s i d e groups d e c r e a s e s t h e f l e x i b i l i t y o f t h e polymer c h a i n and t h e g l a s s t r a n s i t i o n t e m p e r a t u r e s o f m o d i f i e d polymers i n c r e a s e s . T h i s

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

52

CHEMICAL REACTIONS ON POLYMERS

Table I I I .

M o d i f i c a t i o n o f PPO under F r i e d e l - C r a f t s (PPO 5% S o l u t i o n i n N i t r o b e n z e n e )

Reaction Conditions No.

Modifying

PPO:M.A.:A1C1

Agent

(mol:mol:mol)

Sulfonyl

3

Time

Conditions

Substitution

Temperature e

degree

(hours)

( C)

(mol %)

Chlorides

1.

N(CH ) S0 C1

1.

2.

C H S0 C1

1. 0: 1. 0: 1. 10

7 .0

80

60. 7

3.

BrC H S0 Cl

1. 0::1. 0: 1. 10

9.,5

80

59. 0

4.

CH C H S0 C1

1..0::1.,0::1.,10

7.,5

80

66. 6

3

6

2

5

2

2

6

4

3

6

2

4

2

5.

(CH ) C H S0 C1

1.,0::1.,0::1.,10

7..0

60

46. ,3

6.

j^^j^^j^o ci

1..0::1..0::1..10

8..5

80

63. ,5

1..0 :1 .0::1 .10

4 .0

50

42, .7

3

3

a

6

2

2

2

Acid Chlorides : 7 . C H C0C1 2

5

8.

CH (CH ) C0C1

1 .0 :1 .0 :1 .10

3 .0

50

58 .6

9.

CH (CH ) C0C1

1 .0 :1 .0 :1 .10

6 .0

50

59 .0

10. . C H ( C H ) C 0 C 1

1 .0 :0 .5 :0 .55

3 .0

50

17 .5

11. , C H ( C H ) C 0 C 1

1 .0 :1 .0 :1 .10

6 .0

50

55 .0

12. , C H ( C H ) C 0 C 1

1 .0 :1 .0 :1 .10

6 .5

50

50 .0

13. , C H C H C 0 C 1

1 .0 :0 .5 :0 .55

6 .0

50

29 .2

14. , C H C H C 0 C 1

1 .0 :1 .0 :1 .10

8 .0

60

79 . 4

3

2

3

2

3

2

3

6

)

2

5

3

1 Q

2

3

a

2

1 2

1 2

1 4

2

6

4

1

d e t e r m i n e d by H NMR M.A. - m o d i f y i n g agent

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

4.

P E R C E C A N D LI

10

8

Poly(2,6-dimethyl-l,4'phenylene

6

4

oxide)

2

δ (ppm) 1

Figure 1. H NMR spectra of PPO ( I ) , PPO modified with benzene sulfonyl chloride (Sample No. 2, Table III) ( I I ) , and PPO modified with p-toluenesulfonyl chloride (Sample No. 4, Table III) (III) Reproduced with permission from Ref. 17. Copyright 1987, Wiley.)

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

54

CHEMICAL REACTIONS ON POLYMERS

I.CH3

yCH

"CH

t

3

a

φι:: CH t f

3

3

VI

CH

t a

c =o

I CH -f I CH *-e I

3

3

2

2

(CH ) -g CH, *-d 2

2.0

1 0

d

\

1.0

CH

Q-o-dI^CH C = 0 I ÇH -f

p CC H f

3

3

O3

t

2

6.5

1.75

c

Vf

10

3.0

\

6

4 δ

M

I

2

CH -d 3

IV

(ppm)

Figure 2. H NMR spectra of PPO acylated with propionyl chloride (Sample No. 8, Table III) (IV), PPO acylated with myristoyl chloride (Sample No. 11, Table III) (V), and PPO acylated with £-toluoyl chloride (Sample No. 14, Table III) (VI). (Reproduced with permission from r e f . 17. Copyright 1987 Wiley.)

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988. 0-150

10

11

PPO a c y l a t e d w i t h myristoyl chloride

PPO a c y l a t e d w i t h myristoyl chloride

Source:

0-250

PPO s u l f o n y l a t e d with dimethyl sulfamoyl chloride

Reproduced with permission from Ref. 17.

0-200

100-200

PPO s u l f o n y l a t e d with p-toluenesulfonyl chloride

CO

75-175

Table I I I

200-300

150-300

250-325

200-300

175-300

CO

0.1

0.7

1.9

0.2

0.6

(%)

Weight L o s s

Zone I I Temp. Range

Copyright 1987, Wiley.

0.0

0.0

0.0

0.4

0.3

(%)

Weight L o s s

Zone I Temp. Range

PPO

Polymer

Number

Thermal C h a r a c t e r i z a t i o n o f PPO M o d i f i e d by F r i e d e l - C r a f t s

Corresponding t o

T a b l e IV.

300-400

300-400

325-400

300-400

300-400

CO

Temp. Range

3.0

2.5

11.7

3.5

0.2

(%)

Weight L o s s

Zone I I I

Reactions

T

G

165

116

245

225

212

CO

56

CHEMICAL REACTIONS ON POLYMERS

e f f e c t was e x e m p l i f i e d by t h e PPO m o d i f i e d w i t h p - t o l u e n e s u l f o n y l c h l o r i d e which has a T o f 2 6 5 C . S i m i l a r l y an i n c r e a s e i n t h e v a l u e o f t h e T was a l s o o b s e r v e d when PPO was m o d i f i e d w i t h p o l a r s u b s t i t u e n t s such as d i m e t h y l s u l f a m o y l group. In t h i s case t h e T v a l u e was 245*C. The i n c r e a s e i n t h e l e n g t h o f t h e s i d e c h a i n r e s u l t s n o r m a l l y i n an i n t e r n a l p l a s t i c i z a t i o n e f f e c t c a u s e d by a lower p o l a r i t y o f t h e main c h a i n and an i n c r e a s e i n t h e c o n f i g u r a t i o n a l e n t r o p y . Both e f f e c t s r e s u l t i n a lower a c t i v a t i o n e n e r g y o f segmental m o t i o n and c o n s e q u e n t l y a lower g l a s s t r a n s i t i o n t e m p e r a t u r e . The m o d i f i c a t i o n o f PPO w i t h m y r i s t o y l c h l o r i d e o f f e r s t h e b e s t example. No s i d e c h a i n c r y s t a l l i z a t i o n was d e t e c t e d by DSC f o r t h e s e p o l y m e r s . The s u l f o n y l a t e d and a c y l a t e d PPO p r e s e n t s s o l u b i l i t y c h a r a c t e r i s t i c s which a r e c o m p l e t e l y d i f f e r e n t from t h o s e o f t h e p a r e n t PPO. T a b l e V p r e s e n t s t h e s o l u b i l i t y o f some m o d i f i e d s t r u c t u r e s compared t o t h o s e o f u n m o d i f i e d PPO. I t i s v e r y i m p o r t a n t t o n o t e t h a t , a f t e r s u l f o n y l a t i o n , most o f t h e polymers become soluble i n dipolar aproti N,Nd i m e t h y l f o r m a m i d e (DMF the same t i m e i t i s i n t e r e s t i n g t o mention t h a t , w h i l e PPO c r y s t a l l i z e s f r o m methylene c h l o r i d e s o l u t i o n , a l l t h e s u l f o n y l a t e d p o l y m e r s do n o t c r y s t a l l i z e and form i n d e f i n i t e l y s t a b l e s o l u t i o n s i n m e t h y l e n e c h l o r i d e . O n l y some o f t h e a c e t y l a t e d p o l y m e r s become s o l u b l e i n DMF and DMAC, and none a r e s o l u b l e i n DMSO. The polymers a c e t y l a t e d w i t h a l i p h a t i c a c i d c h l o r i d e s such as p r o p i o n y l c h l o r i d e are a l s o s o l u b l e i n acetone. The p e r m e a t i o n p r o p e r t i e s o f s u b s t i t u t e d PPO t o a c a r b o n d i o x i d e , methane, n i t r o g e n m i x t u r e were s t u d i e d f o r s e v e r a l systems. The r e s u l t s a r e presented i n Table V I . An i n c r e a s e i n p e r m e a b i l i t y t o g e t h e r w i t h an i n c r e a s e i n s e l e c t i v i t y f o r CO2/CH4 was c l e a r l y d e m o n s t r a t e d f o r PPO s u b s t i t u t e d w i t h p - t o l u e n e s u l f o n y l c h l o r i d e and f o r PPO s u b s t i t u t e d w i t h d i m e t h y l s u l f a m o y l c h l o r i d e (Table V I ) . An i n t e r e s t i n g example i s PPO m o d i f i e d w i t h m y r i s t o y l c h l o r i d e . This long side chain s u b s t i t u t e d polymer showed an i n c r e a s e i n p e r m e a b i l i t y f o r methane of 5.19 t i m e s w h i l e i t s p e r m e a b i l i t y f o r c a r b o n d i o x i d e remained almost unchanged. T h e r e f o r e i t s s e l e c t i v i t y t o C0 /CH d e c r e a s e s d r a m a t i c a l l y compared t o t h a t o f t h e p a r e n t polymer. However i t c a n be s p e c u l a t e d t h a t by v a r y i n g t h e l e n g t h o f t h e s i d e c h a i n o f t h e m o d i f i e d s t r u c t u r e s , c e r t a i n d i f f e r e n c e s i n p e r m e a b i l i t y among d i f f e r e n t h y d r o c a r b o n gases a r e l i k e l y t o o c c u r . T h i s i s an i m p o r t a n t a s p e c t which may p r o v e u s e f u l f o r h y d r o c a r b o n / h y d r o c a r b o n separations. e

G

G

G

2

4

Conclusions C h e m i c a l m o d i f i c a t i o n s o f PPO by e l e c t r o p h i l i c s u b s t i t u t i o n o f t h e a r o m a t i c backbone p r o v i d e d a v a r i e t y o f new s t r u c t u r e s w i t h improved gas p e r m e a t i o n c h a r a c t e r i s t i c s . I t was f o u n d t h a t t h e s u b s t i t u t i o n degree, main c h a i n r i g i d i t y , t h e b u l k i n e s s and f l e x i b i l i t y o f t h e s i d e c h a i n s and t h e p o l a r i t y o f t h e s i d e c h a i n s a r e major p a r a m e t e r s c o n t r o l l i n g t h e gas p e r m e a t i o n p r o p e r t i e s o f the polymer membrane. The b r o a d range o f s o l v e n t s a v a i l a b l e f o r t h e m o d i f i e d s t r u c t u r e s enhances t h e p o s s i b i l i t y o f f a c i l e p r e p a r a t i o n o f PPO b a s e d membrane systems f o r use i n gas s e p a r a t i o n s .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Benzenesulfonyl chloride

ρ-Toluenesulfonyl c h l o r i d e

Naphthalenesulfonyl chloride

Dimethylsulfamoyl

p-Toluoyl chloride

Propionyl chloride

Lauroyl chloride

Palmitoyl chloride

Phenyl

S o l u b l e > 1 g/100 ml Insoluble

Tendency t o c r y s t a l l i z e

2.

3.

4.

5.

6.

7.

8.

9.

10.

+

+

Source:

None

1.

from

solution

+

+

+

+

+

+

+

+

+

+

-

+

+

-

-

+

+

-

+

+

+

+

-

+

+

+

±

±

DMSO

Reactions

+

+

+

+ +

+

+

DMF

Solvent

C o p y r i g h t 1987, W i l e y .

Chloroform

Methylene Chloride

o f PPO M o d i f i e d by F r i e d e l - C r a f t s

Reproduced w i t h p e r m i s s i o n from Ref. 17.

acetyl chloride

chloride

Modifying Agent

Solubility

No.

T a b l e V.

+

-

-

+

+

+

+

+

+

DMAC

+

+

+

+

+

+

+

+

+

THF

Acetone

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Dimethylsulfamoyl

Myristoyl chloride (Polymer 11, T a b l e I I I )

3.

4.

Testing

Toluenesulfonyl

2.

e

t e m p e r a t u r e = 25 C

chloride

None

1.

chloride

Agent

CH 4

20.26

3.31

3.20

3.90

p

The P e r m e a b i l i t y

No.

Modifying

Table VI.

co 2

58.09

80.99

75.00

64.00

(barrer)

p

N 2

11.84

2.45

1.55

3.30

P

t o Gases o f PPO M o d i f i e d

a

2.87

24.47

23.40

16.40

2

C0 /CH

by F r i e d e l - C r a f t s

4

a

4

1.71

1.35

2.06

1.18

CH /N

Reactions

2

4. P E R C E C A N D LI

Poly(2,6-dimethyl-l,4-phenylene oxide)

59

References 1. A.J. Erb and D.R. Paul, J. Membr. Sci., 8, 11 (1981). 2. D.R. Paul, J. Membr. Sci., 18, 75 (1984). 3. J.W. Barlow and D.R. Paul, J. Appl. Polym. Sci., 21, 845 (1984). 4. K. Toi, G. Morel and D.R. Paul, J. Appl. Polym. Sci., 27, 2997 (1982). 5. L. Verdet and J.K. Stille, Organometallics, 1, 380 (1982). 6. R. P. Kambour, J. T. Bendler and R. C. Bopp, Macromolecules, 16, 753 (1983). 7. A.J. Chalk and A.S. Hay, J. Polym. Sci., Part A-1. 7, 691 (1968). 8. S. Xie, W.J. MacKnight and F.E. Karasz, J. Appl. Polym. Sci., 29, 1678 (1984). 9. I. Cabasso, J.J. Grodzinski and D. Vofsi, J. Appl. Polym. Sci., 18, 1969 (1974). 10. D.M. White and C.M 11. W.J. Ward III and Rober Pat. 3,780,496 (1973). 12. G. Li, U.S. Pat. 4,521,224 (1985). 13. E.S. Percec and G. Li, U.S. Pat. 4,596,860 (1986). 14. R.A. Pasternak, J.F. Schimscheimer and J. Heller, J. Polym. Sci., Part A-2, 8, 467 (1970). 15. C.E. Rogers, in Recent Development in Separation Science, Vol. II, N.N. Li ed., CRC Press, p. 107, 1975. 16. G.A. Olaf, S. Kobayashi and J. Nishimura, J. Am. Chem. Soc., 564 (1973). 17. S. Percec, J. Appl. Polym. Sci., 33, 191 (1987). R E C E I V E D August 27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 5

Synthesis and Reactions of Halogenated Polyethers and Polysulfides 1

2

Melvin P. Zussman , Jenn S. Shih , Douglas A. Wicks, and David A. Tirrell Polymer Science and Engineering Department, University of Massachusetts, Amherst, M A 01003

Halogenated polyether d polysulfide t number of interestin of the reactivity polyme desig of new reactive polymers. In this chapter, we explore the consequences of side chain extension, leaving group variation, and neighboring group participation in determining the stability and reactivity of these two classes of polymeric materials. P o l y e p i c h l o r o h y d r i n (PECH) i s well known as a r e a c t i v e e l a s t o m e r . D i s p l a c e m e n t at t h e c a r b o n - c h l o r i n e bond of PECH has been accom­ p l i s h e d with a wide v a r i e t y of n u c l e o p h i l i c r e a g e n t s , f o r t h e pur­ poses o f polymer m o d i f i c a t i o n , g r a f t i n g and c r o s s l i n k i n g ( l _ 2 ) . On the o t h e r hand, t h e PECH s t r u c t u r e (1) i s h a r d l y optimal from t h e p o i n t o f view of i t s r e a c t i v i t y as a~substrate f o r n u c l e o p h i l i c 9

1

substitution: c h l o r i d e i s modest i n i t s l e a v i n g group a b i l i t y , and t h e β-branch p o i n t ( i . e . t h e c h a i n backbone) would be expected t o d e p r e s s r e a c t i o n r a t e s by a f a c t o r o f 10 or so {3). W i t h i n t h e past s e v e r a l y e a r s , we have examined t h e s y n t h e s i s and r e a c t i o n s of s e v e r a l c l a s s e s of polymers r e l a t e d t o PECH. We have adopted t h r e e simple approaches t o t h e p r e p a r a t i o n of p o l y m e r i c s u b s t r a t e s more r e a c t i v e than PECH toward n u c l e o p h i l i c s u b s t i t u t i o n . We have: i ) . removed t h e β-branch p o i n t by e x t e n s i o n of the s i d e c h a i n , i i ) . r e p l a c e d t h e c h l o r i d e l e a v i n g group by a more r e a c t i v e bromide and i i i ) . r e p l a c e d t h e backbone oxygen atom by a s u l f u r atom t h a t o f f e r s s u b s t a n t i a l a n c h i m e r i c a s s i s t a n c e t o n u c l e o p h i l i c 1

2

Current address: Ε. I du Pont de Nemours and Company, Experimental Station, Wilmington, D E 19898

Current address: G A F Corporation, Wayne, N J 07470 0097-6156/88/0364-0060$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

5.

Halogenated Polyethers and Polysulfides

ZUSSMAN ET AL.

61

displacement. Each of these s i m p l e s t r u c t u r a l changes a f f o r d s e l a s t o m e r i c polymers more r e a c t i v e than PECH toward a t t a c k by nucleophilic species. We p r e s e n t i n t h i s c h a p t e r an overview of the s y n t h e s i s and r e a c t i o n s of t h e s e new r e a c t i v e p o l y m e r s . S i d e Chain

Extension

The r e p e a t i n g u n i t s t r u c t u r e of PECH would suggest t h a t t h e r e ­ a c t i v i t y o f the polymer would be r a t h e r s i m i l a r t o t h a t of i s o b u t y l chloride. The e-oxygen atom would not be expected t o o f f e r s u b s t a n ­ t i a l a n c h i m e r i c a s s i s t a n c e i n n u c l e o p h i l i c d i s p l a c e m e n t , and should perhaps be m i l d l y d e a c t i v a t i n g as a r e s u l t of a small i n d u c t i v e effect . In g e n e r a l , the r e a c t i v i t y of i s o b u t y l h a l i d e s toward n u c l e o p h i l i c reagents i s depressed i n comparison with the r e a c t i v i t y of primary, s t r a i g h t - c h a i n analogues. S t r e i t w i e s e r l i s t s compara­ t i v e data f o r nine r e a c t i o n s of i s o b u t y l and 1-propyl h a l i d e s {3); w i t h i n t h i s s e t , kp py-|/k-jsobutyl fro 4 . 3 ( f o RB Cl" i acetone) t o 3 3 . 8 ( f o r R The β-branch p o i n t of h i g h e r l , 2 - e p o x y - a ) - c h l o r o a l k a n e s . Such polymers are r e a d i l y prepared by treatment of the neat monomers with the m o d i f i e d t r i ethylaluminum c a t a l y s t i n t r o d u c e d by Vandenberg (5_,6J ; r e s u l t s f o r ( 2 - c h l o r o e t h y l ) o x i r a n e , ( 3 - c h l o r o p r o p y l ) o x i r a n e and ( 4 - c h l o r o b u t y l ) o x i r a n e (2a-c) are summarized i n T a b l e I (7_,8). r0

2a:

δ, Ζ tr°i

η =2 η =3 η

Table m™™™ Monomer

a

(CH )CH C1 n-i

4

I.

2

Homopolymerization

Polymerization ^ (

p

a

y

s

D

ν

2

2

(Chloroalkyl)oxiranes

,· -ΐΛ

Yield

)

Λ

fo,\

(%)

*inh (

d

L

/

g

Tn(°r\ Tg( C)

D )

2a

14

89

4.12

2b

14

78

3.44C

-42

2c

10

77

1.21

-50

Polymerization

at room temperature

AlEt3/H20/acetylacetone c

3

of

(CH )CH C1 n-i

2

In CHC13,

c

-27

i n presence of 5 mol-%

(1/0.5/0.5)

0.5 wt %, 35°C

GPC peak m o l e c u l a r weight

> 10

6

In each c a s e , the polymer i s o b t a i n e d as a white e l a s t o m e r of high m o l e c u l a r weight (>10 i n some e x p e r i m e n t s ) . Each of t h e s e polymers i s s o l u b l e i n benzene, i n c h l o r i n a t e d hydrocarbons and i n dipolar aprotic solvents. F i g u r e 1 shows t h e k i n e t i c s of c h l o r i d e s u b s t i t u t i o n by tetra-n-butylammonium benzoate i n Ν , Ν - d i m e t h y l a c e tamide at 50°C, f o r PECH and f o r the polymers of 2 a - c . Under t h e s e c o n d i t i o n s , each of the h i g h e r homologues i s a b o u t ~ e q u a l l y r e a c t i v e , and a l l are c o n v e r t e d t o the benzoate more r a p i d l y than PECH. Each 6

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CL

c ο

70

80

90

100

2

ι

1

1

2

1

12

1

n

1

1

η = 1

1

2

1

Time

14

(hr)

16

1

NBU4

DMAc, 5 0 *

PhC0

1

18

1

20

2

1

1

1

n

22

2

2

1

24

1

(CH ) 0 CPh

-CH -CH-O-

Kinetics of Substitution

10

2

(CH f CI

-CH -CH-0-

-τ

26

1

1

1

28

30

-

-

r-•>»—

F i g u r e 1. C o n v e r s i o n v e r s u s time f o r s u b s t i t u t i o n by tetrabutylammonium benzoate on p o l y ( e p i c h l o r o h y d r i n ) (Δ, A , s e p a r a t e r u n s ) ; p o l y [ ( 2 - c h l o r o e t h y l ) o x i r a n e ] ( O ) ; p o l y [ ( 3 - c h l o r o p r o p y l ) o x i r a n e ] ( V ) ; and p o l y [ ( 4 - c h l o r o b u t y l ) o x i r a n e ] ( • ) . (Reproduced w i t h p e r m i s s i o n from réf. 1. C o p y r i g h t 1982 W i l e y . )

Γ

Γ

P i * *

1 I / I

' 1 $

ι

W

ο *d Ο r *! S

ζ

Ο

u

>

w

>

n

s

w

5.

ZUSSMAN ET AL.

Halogenated Polyethers and Polysulfides

63

of t h e s e r e a c t i o n s shows n e g a t i v e d e v i a t i o n s from s e c o n d - o r d e r k i n e ­ t i c s , but s e c o n d - o r d e r r a t e c o n s t a n t s can be e s t i m a t e d from the i n i t i a l reaction rates. T h i s procedure g i v e s a s e c o n d - o r d e r r a t e c o n s t a n t of 3.9 χ M" s " f o r p o l y [ ( 2 - c h l o r o e t h y l ) o x i rane] and a v a l u e of 0.63 χ 10" * M" s " f o r PECH. Thus the h i g h e r homologues are more r e a c t i v e than PECH by a f a c t o r of 6 , an o b s e r v a t i o n com­ p l e t e l y c o n s i s t e n t with known s t r u c t u r e - r e a c t i v i t y r e l a t i o n s f o r simple alkyl h a l i d e s . The r e a c t i v e c a r b o n - c h l o r i n e bond i n t h e s e p o l y e t h e r s a l l o w s t h e i r conversion to other i n t e r e s t i n g m a t e r i a l s . For example, q u a n t i t a t i v e c h l o r i d e d i s p l a c e m e n t by benzoate anion f o l l o w e d by basic methanolysis affords h y d r o p h i l i c polyether elastomers that are w a t e r - s o l u b l e or w a t e r - s w e l l a b l e , depending on s i d e c h a i n l e n g t h (9). Poly[(3-hydroxypropyl)oxirane] i s a c o l o r l e s s elastomer that can be c a s t i n t o t o u g h , c l e a r f i l m s from water or m e t h a n o l . Poly[ ( 4 - h y d r o x y b u t y l ) o x i r a n e ] i s i n s o l u b l e i n w a t e r , but q u i t e h y d r o ­ p h i l i c ; a f i l m immersed i wate gain 46% i weight i 90 mi t room t e m p e r a t u r e , w h i l e f o r such m a t e r i a l s as a d h e s i v e s l e n s e s may be a n t i c i p a t e d . 1

Bromide as L e a v i n g

1

1

1

1

Group

Perhaps the most s t r a i g h t f o r w a r d approach t o i n c r e a s i n g the r e a c t i v i t y of halogenated s u b s t r a t e s - - p o l y m e r i c or o t h e r w i s e - - i s t o e x p l o i t the well known o r d e r of l e a v i n g group a b i l i t y , i . e . , I > Br > Cl > F. For example, data p r o v i d e d by S t r e i t w i e s e r suggest t h a t replacement of c h l o r i d e by bromide w i l l l e a d t o r a t e enhance­ ments of 50- t o 2 0 0 - f o l d , depending on r e a c t i o n c o n d i t i o n s (3_). One cannot take t h i s approach too f a r i n the d e s i g n of r e a c t i v e p o l y ­ m e r i c s u b s t r a t e s , however, s i n c e the l e a v i n g group must be i n e r t t o t h e c o n d i t i o n s of p o l y m e r i z a t i o n i f p r o t e c t i o n - d e p r o t e c t i o n schemes are t o be a v o i d e d . The i d e a l l e a v i n g group would be c o m p l e t e l y u n r e a c t i v e toward the n u c l e o p h i l i c s p e c i e s i n v o l v e d i n c h a i n growth, but r e a d i l y d i s p l a c e d i n subsequent polymer m o d i f i c a t i o n r e a c t i o n s . Bromide appears t o be u s e f u l i n t h i s r e g a r d . T a b l e II sum­ m a r i z e s our homopolymerization experiments on ( 2 - b r o m o e t h y l ) o x i r a n e , ( 3 - b r o m o p r o p y l ) o x i r a n e and ( 4 - b r o m o b u t y l ) o x i r a n e ( 3 a - c ) ( 1 0 - 1 2 ) .

3a:

η η =2

~b:

η η =3

c:

η =4

(CH )CH Br n-i 2

2

(CH )CH Br n-i 2

2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

64

CHEMICAL REACTIONS ON POLYMERS

Table M^n^mo^ Monomer

a

b

c

II.

Homopolymerization Polymeri z a t i on ^

Γ*+*Ι„*>+

Catalyst

e

(

h

p

)

of

(Bromoalkyl)oxiranes Yield ( % )

^inh ( ( j L / g )

3a

a

24

67

3.5

3a

b

24

63

0.6

3b

a

3

35

0.6

3b

b

24

74

0.5

3c

a

24

65

1.7

3c

b

24

68

0.6

Room t e m p e r a t u r e ,

6-7 mol-X A l E t / H 0 / a c e t y l a c e t o n e

Room t e m p e r a t u r e ,

6-7

c

/ \ Tg ( C) T r t

0 r

-35 -35 -34 (1/0.5/1)

In C H C 1 , 0.5 wt %, 30°C 3

P o l y m e r i z a t i o n of each of these o x i r a n e s i s e f f e c t i v e l y accom­ p l i s h e d by treatment of the neat monomer with the c h e l a t e d aluminum catalyst. It i s i n t e r e s t i n g t o note t h a t h i g h e r m o l e c u l a r weights are g e n e r a l l y r e a l i z e d by u s i n g the c a t a l y s t mixture t h a t c o n t a i n s a 1:1 r a t i o of t r i e t h y l a l u m i n u m and a c e t y l a c e t o n e ; t h i s may be a r e ­ s u l t of c h e l a t i o n of the most a c i d i c c a t a l y s t s i t e s and a consequent r e d u c t i o n i n c h a i n t r a n s f e r a s s o c i a t e d with A l - a s s i s t e d i o n i z a t i o n o f the C-Br bond. The poly[(a>-bromoalkyl ) o x i r a n e ] s are s l i g h t l y t a c k y e l a s t o m e r s at room t e m p e r a t u r e ; a l l undergo a g l a s s t r a n s i t i o n at a p p r o x i m a t e l y - 3 5 ° C . F i g u r e 2 shows t h e k i n e t i c s of bromide s u b s t i t u t i o n by t e t r a - n butylammonium benzoate i n CDC1 at 45°C, f o r p o l y ( e p i b r o m o h y d r i n ) (PEBH) and f o r the polymers of 3 a - c . Although these r e s u l t s are not d i r e c t l y comparable t o those i n ~ F i g u r e 1 because of d i f f e r e n c e s i n s o l v e n t s and t e m p e r a t u r e s , q u a l i t a t i v e c o n s i s t e n c y i s a p p a r e n t . F i r s t of a l l , each o f the h i g h e r homologues i s about e q u a l l y r e ­ a c t i v e , and a l l r e a c t more r a p i d l y than PEBH. The k i n e t i c s show n e g a t i v e d e v i a t i o n from s e c o n d - o r d e r b e h a v i o r , as b e f o r e , but the i n i t i a l s l o p e s of the s e c o n d - o r d e r p l o t s are again u s e f u l f o r com­ p a r a t i v e purposes. T a b l e I I I l i s t s the r a t e c o n s t a n t s o b t a i n e d i n t h i s way. As i n t h e c h l o r i d e s e r i e s , e x t e n s i o n of the s i d e c h a i n by a s i n g l e carbon atom removes the s-branch p o i n t and a c c e l e r a t e s the r e a c t i o n by a f a c t o r of about 10. (The s i g n i f i c a n c e of the apparent t w o - f o l d h i g h e r r e a c t i v i t y of the 3-bromopropyl s i d e c h a i n compared t o i t s 2- and 4-carbon homologues has not been d e t e r m i n e d . ) F i n a l l y , the bromides are indeed more r e a c t i v e than the c h l o r i d e s ; d e s p i t e the use o f CDC1 as the r e a c t i o n s o l v e n t , the bromides r e a c t more than an o r d e r of magnitude f a s t e r than t h e c h l o r i d e s , even though the l a t t e r were c o n v e r t e d i n DMAc, a s u p e r i o r s o l v e n t f o r n u c l e o ­ p h i l i c s u b s t i t u t i o n s of t h i s k i n d . 3

3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

5.

ZUSSMAN ET AL.

Halogenated Polyethers and Polysulfides

TIME

( hrs )

F i g u r e 2. C o n v e r s i o n v e r s u s time f o r s u b s t i t u t i o n by t e t r a b u t y l ammonium benzoate on p o l y ( e p i b r o m o h y d r i n ) (O) ; p o l y [ ( 2 - b r o m o e t h y l ) o x i r a n e ] ( 0 ) ; po1y[(3-bromopropyl)oxirane] (v, separate r u n s ) ; and p o l y [ ( 4 - b r o m o b u t y l ) o x i r a n e ] ( • , separate r u n s ) .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

65

66

CHEMICAL REACTIONS ON POLYMERS Table

III. on

S i d e Chain Length

c

b

b

2

χ 10"

2

6.97

χ ΙΟ"

3

4.53

χ 10"

4

3.88

χ ΙΟ-

CDC1

(M"

0

0

8.57

3

3

3

1.74

χ ΙΟ"

1.40

χ ΙΟ"

9.11

χ ΙΟ"

8.10

χ ΙΟ"

3

s-i)

1

2

0.8

χ ΙΟ"

2

8.2

χ

10-3

19 χ Ι Ο "

3

7.9

3

Concentrations

Initial

slope

of

second-order

Assistance

b

kinetic

χ ΙΟ"

Table

Backbon

Sulfu

IV.

Relative

organic for

Rate C o n s t a n t s f o r H y d r o l y s i s of A l k y l C h l o r i d e s 3

CH CH CH CH C1

1.00

CH CH 0CH CH C1

0.18

3

3

2

2

2

2

2

2

CH CH SCH CH C1 3

2

2750

2

0.77

CH CH SCH CH CH C1

1.00

3

a Aqueous d i o x a n e , relative

2

CH CH 0CH CH CH C1 3

Rate

3

3

plot

The a c c e l e r a t i o n of h a l i d among the most f a m i l i a r examples of a n c h i m e r i c a s s i s t a n c e i n chemistry. T a b l e IV i l l u s t r a t e s the magnitude of the e f f e c t primary a l k y l c h l o r i d e s (4_).

b

3

3

Initial

Anchimeric

[Benzoate] (M)

[-CH Br] (M)

1

a 45°C, b

K i n e t i c s of S u b s t i t u t i o n Poly(u)-bromoalkyl)oxiranes

to

2

2

2

2

[H 0] 2

2

2

2

2

= 20 M, 100°C

1-chlorobutane

A 6 - s u l f i d e a c c e l e r a t e s the s o l v o l y s i s n e a r l y 3 0 0 0 - f o l d compared t o the s i m p l e a l k y l h a l i d e and a p p r o x i m a t e l y 1 5 , 0 0 0 - f o l d compared t o the β - c h l o r o e t h e r . On the o t h e r hand, the γ - s u l f i d e o f f e r s no a s s i s t a n c e ; a p p a r e n t l y c l o s u r e t o the four-membered c y c l i c s u l f o n ium ion cannot compete with d i r e c t d i s p l a c e m e n t by the e x t e r n a l nucleophile. These r e s u l t s suggest t h a t p o l y [ ( c h l o r o m e t h y l ) t h i i r a n e ] (PCMT, 4) s h o u l d be s u b s t a n t i a l l y more r e a c t i v e than p o l y e p i c h l o r o h y d r i n

4

toward n u c l e o p h i l i c s u b s t i t u t i o n s , and indeed i t i s ( 1 3 ) . In a d d i t i o n , the f o r m a t i o n of the i n t e r m e d i a t e e p i s u l f o n i u m ion by

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

5.

ZUSSMAN ET AL.

67

Halogenated Polyethers and Polysulfides

n e i g h b o r i n g group d i s p l a c e m e n t leads t o a rearrangement of the CMT r e p e a t i n g u n i t t o one (5) d e r i v e d from t h e r i n g - opening p o l y m e r i z a ­ t i o n of 3 - c h l o r o t h i e t a n e (3CT, Scheme I) (13^17)·

Δ

{CH CH-S3- 2

CH

{CH CH-S} 2

^

k

- i

\ l

C 1

2

KH CH-S3^CH2CHCH -S} 2

2

CH C1

CH C1

4

k ,k_

2

Ù

rl

\ / CH

I

"

6

ÎCH ÇHCH -Sl

2

2

Cl

2

2

CI

k

k

Scheme I We have examined t h e e f f e c t s of c o n c e n t r a t i o n , t e m p e r a t u r e , s o l v e n t and added e l e c t r o l y t e on the k i n e t i c s of t h i s s t r u c t u r a l interconversion. In a l l i n s t a n c e s , the k i n e t i c s are well d e s c r i b e d by the r a t e law f o r a r e v e r s i b l e f i r s t - o r d e r r e a c t i o n [ E q u a t i o n 1 ] :

f ( 3 C T ) - foo(3CT)" 0

(K + K")t = In

(1)

f(3CT) - U 3 C T ) where f(3CT) i s the f r a c t i o n of 3 - c h l o r o t h i e t a n e r e p e a t i n g u n i t s i n t h e copolymer and the s u b s c r i p t s 0 and » r e f e r t o i n i t i a l and e q u i l i b r i u m copolymer s t r u c t u r e s , r e s p e c t i v e l y ; Κ and K~ are c o m b i n a t i o n s of the elementary r a t e c o n s t a n t s k , k , k . and k_ ( c f . Scheme I) such t h a t x

Κ =

,

2

L

, + k,

2

(2)

and k_,kk.i

+ k

(3) 2

The q u a n t i t y (K + K") i s thus o b t a i n e d as the s l o p e of a p l o t r i g h t s i d e of E q u a t i o n 1 v e r s u s t i m e , and because

f

(

3

C

T

)

»

=

τττ-

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

of the

( 4 )

68

CHEMICAL REACTIONS ON POLYMERS

the composite r a t e c o n s t a n t s K and K" can be determined i n d i v i d u ­ ally. Each of t h e s e q u a n t i t i e s (K and K") may be viewed as a r a t e c o n s t a n t f o r c y c l i z a t i o n , m u l t i p l i e d by a f a c t o r t h a t d e s c r i b e s the p a r t i t i o n i n g of the s u l f o n i u m ion i n t e r m e d i a t e between the two i s o ­ m e r i c p r o d u c t s of c h l o r i d e ion a t t a c k . T a b l e V summarizes the v a l u e s of (K + K") o b t a i n e d i n t h i s way:

Table

V.

K i n e t i c s of Repeating Unit I s o m e r i z a t i o n i n P o l y [ ( c h l o r o m e t h y l ) t h i i r a n e ] and Poly(3-chlorothietane)

Temperature (°C)

Solvent

48

none

40

none

35

none

20.5

none

35.5

none

35.5

CHC1

35.5

N0 Ph

35.5

CD C1

3

35.5

CD Cl c

0.55

3

b

c

d

e

Equilibrium Fraction 3CT U n i t s 0.685

3

3

0

2

PCMT-E ( r e f

15)

P3CT ( r e f Calculated

1.2

0.675

± .03

0.59

± .03

0.33 ± 0.04

0.62

± .03

0.47

0.55

± .02e

0.42 ± 0.06

± .02e

0.36 ± 0.07

b 3 b

2

15)

6.3 ± 1.6

d

3

2

PCMT-C ( r e f

6

9.4 ± 0 . 9

± .04

0.690

3

Κ + K- ( 1 0 " s

2

2

± 0.14 ± 0.09

15) from r e s u l t

Based on rearrangement

at 48°C of

P3CT

These data reveal s e v e r a l i n t e r e s t i n g f e a t u r e s of the r e p e a t i n g unit isomerization. F i r s t of a l l , the r a t e c o n s t a n t s are of roughly t h e same o r d e r of magnitude as t h o s e observed i n s o l v o l y s e s and r e ­ arrangements of B - c h l o r o s u l f i d e s of low m o l e c u l a r weight when d i f f e r ­ ences i n s o l v e n t s and temperatures are taken i n t o a c c o u n t . T a b l e VI p r o v i d e s a summary of comparative data from the l i t e r a t u r e . We have a l s o determined the apparent r a t e c o n s t a n t f o r the analogous isom­ e r i z a t i o n of l - c h l o r o - 2 - e t h y l t h i o p r o p a n e (7) t o 2 - c h l o r o - l - e t h y l t h i o p r o p a n e (8) t o be 4 χ 1 0 s at 45°C Τη the absence of s o l v e n t . The l a t t e r i s ~ o f c o u r s e a composite r a t e c o n s t a n t of the kind d e f i n e d by E q u a t i o n s 2 and 3. _ 6

7

1

8

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

5.

Halogenated Polyethers and Polysulfides

ZUSSMAN ET AL.

Table VI.

Substrate

Rates and A c t i v a t i o n E n e r g i e s o f R e a c t i o n s of 6 - C h l o r o s u l f i d e s

Temp

Solvent

(°c)

E (kcal/mol)

k(s"

a

40

EtOH/ Η,Ο

1.2 χ 10-5

18.6

PhSCH CH Cl

40

MeOH

2.5 χ ίο-**

18

CH SCH CH C1

55

AcOH

4 . 8 χ ίο- *

2-endo-chloro7-thiabicyclo[2.2.1]heptane

25

AcOH

1.8 χ 10"

CH PhSCH CH Cl 3

2

2

3

2

2

2

2

69

C1 CHCHC1

2

4.5 χ 1 0 "

threo-

C1 CHCHC1

2

9.2 χ 1 0 "

2

18 19 20

1

erythro70 Ph(Cl PhS)CHCHClCH

6 d

Ref

16.4

21

23

22

3

50

Ph(Cl PhS)CHCHClCH a

3

2

22

6 a

(6)

These are composite E q u a t i o n s 2 and 3.

rat

A second p o i n t of i n t e r e s t i s the apparent a c t i v a t i o n energy of the isomen*zation. From an examination of the temperature depend­ ences of Κ and K" f o r r e a c t i o n i n the bulk polymer, we f i n d apparent a c t i v a t i o n e n e r g i e s of 22-23 kcal/mol f o r each of the forward and reverse processes. Given the composite nature of Κ and K , t h e s e are t r u e a c t i v a t i o n e n e r g i e s only i f the p a r t i t i o n i n g of the s u l f o n ium i o n i n t e r m e d i a t e i s i n s e n s i t i v e t o t e m p e r a t u r e . Nonetheless, t h e s i m i l a r i t y of these parameters t o those l i s t e d i n T a b l e VI argues f o r a common mechanism t h a t i n v o l v e s in a l l i n s t a n c e s r a t e d e t e r m i n i n g r i n g - c l o s u r e t o the e p i s u l f o n i u m i o n , as suggested by Scheme I . The s o l e e x c e p t i o n i n T a b l e VI i s the low a c t i v a t i o n energy f o r rearrangement of t h r e o - 6 ; t h i s b e h a v i o r appears t o be anomalous, and no e x p l a n a t i o n i s p r o v i d e d by the o r i g i n a l authors (22). The s o l v e n t dependence of the r e a c t i o n r a t e i s a l s o c o n s i s t e n t w i t h t h i s m e c h a n i s t i c scheme. Comparison of the r a t e c o n s t a n t s f o r i s o m e r i z a t i o n s of PCMT i n c h l o r o f o r m and i n n i t r o b e n z e n e shows a small ( c a . 40%) r a t e enhancement in the l a t t e r s o l v e n t . Simple e l e c t r o s t a t i c theory p r e d i c t s that n u c l e o p h i l i c s u b s t i t u t i o n s in which n e u t r a l r e a c t a n t s are c o n v e r t e d t o i o n i c p r o d u c t s s h o u l d be a c c e l e r a t e d i n p o l a r s o l v e n t s ( 2 3 ) , so t h a t a r a t e i n c r e a s e i n n i t r o b e n z e n e i s t o be e x p e c t e d . In f a c t , t h i s e f f e c t i s o f t e n very small ( 2 4 ) . For example, P a r k e r and co-workers (25) r e p o r t t h a t the Sjs|2 r e a c t i o n of methyl bromide and dimethyl s u l f i d e i s a c c e l e r a t e d by o n l y 50% on changing t h e s o l v e n t from 88% (w/w) methanol-water t o Ν , Ν - d i m e t h y l a c e t a m i d e (DMAc) at low i o n i c s t r e n g t h ; t h i s i s a f a r g r e a t e r change i n s o l v e n t p r o p e r t i e s than t h a t i n v e s t i g a t e d i n the p r e s e n t work. Thus a s m a l l , p o s i t i v e dependence of r e a c t i o n r a t e on s o l v e n t p o l a r i t y i s i m p l i c i t i n the s u l f o n i u m i o n mechanism. A f i n a l o b s e r v a t i o n c o n s i s t e n t with r a t e - d e t e r m i n i n g c y c l i z a t i o n i s t h a t the r e a c t i o n r a t e i s r e l a t i v e l y i n s e n s i t i v e t o added electrolyte. A d d i t i o n of 0.5 e q u i v a l e n t s of t e t r a - n - b u t y l a m m o n i u m c h l o r i d e or t e t r a - n - b u t y l a m m o n i u m a z i d e t o c h l o r o f o r m s o l u t i o n s of - 1

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

70

CHEMICAL REACTIONS O N POLYMERS

PCMT produces very s m a l l , and a p p r o x i m a t e l y e q u a l , i n c r e a s e s i n r a t e . A l t e r n a t i v e r e a c t i o n mechanisms t h a t invoke as r a t e - d e t e r m i n i n g s t e p s e i t h e r i ) . a t t a c k by c h l o r i d e i o n , o r i i ) . u n a s s i s t e d S^l d i s s o c i a t i o n o f t h e c a r b o n - c h l o r i n e bond a r e i n c o n s i s t e n t with t h i s result. Repeating

Unit

Isomerization

v s . Isomerization

Polymerization

Repeating unit i s o m e r i z a t i o n i s s i m i l a r i n several respects t o isomerization polymerization (26,27). Isomerization polymerization may be d e f i n e d as a p r o c e s s whereby a monomer o f s t r u c t u r e A i s c o n v e r t e d t o a polymer o f r e p e a t i n g u n i t s t r u c t u r e B, wherein t h e c o n v e r s i o n o f A t o Β r e p r e s e n t s a s t r u c t u r a l change which i s not a s i m p l e r i n g opening o r double bond a d d i t i o n : nA

— >

m

n

The product of an i s o m e r i z a t i o the r e l a t i v e rates of th propagatio steps; , i t i s k i n e t i c a l l y determined. I f i s o m e r i z a t i o n i s much f a s t e r than p r o p a g a t i o n , t h e homopolymer o f Β i s o b t a i n e d ; c o m p e t i t i v e r a t e s w i l l l e a d t o A-B c o p o l y m e r s . We d e f i n e r e p e a t i n g u n i t i s o m e r i z a t i o n as a p r o c e s s subsequent t o p o l y m e r i z a t i o n , i n which an i n t r a m o l e c u l a r rearrangement o f t h e repeating unit leads to a thermodynamically p r e f e r r e d s t r u c t u r e : ηA

— > «A}

n

— >

-fAMB>y

Thus p r o p a g a t i o n must be much f a s t e r than i s o m e r i z a t i o n , and t h e product w i l l be determined by thermodynamics, r a t h e r than by r e a c ­ tion kinetics. The net r e s u l t s o f t h e two p r o c e s s e s may be q u i t e s i m i l a r , however, i n t h a t polymers of unexpected s t r u c t u r e s may be o b t a i n e d , and copolymers may be prepared by p o l y m e r i z a t i o n o f a s i n g l e monomer. Acknowledgments T h i s work was s u p p o r t e d by g r a n t s from t h e Polymers Program o f t h e National Science Foundation. Support o f our r e s e a r c h by an NSF P r e s i d e n t i a l Young I n v e s t i g a t o r Award i s a l s o g r a t e f u l l y acknowledged.

Literature Cited 1. E. Schacht, D. Bailey and O. Vogl, J. Polym. Sci. Polym. Chem. Ed. 16, 2343 (1978) and references therein. 2. E.J. Vandenberg, in C.C. Price and E.J. Vandenberg, Eds. Coordination Polymerization, Plenum, 1983, p. 11. 3. A. Streitwieser, Jr., Solvolytic Displacement Reactions, McGraw-Hill, New York, 1962. 4. H. Bohme and K. Sell, Chem. Ber., 81, 123 (1948). 5. E.J. Vandenberg, J. Polym. Sci. 47, 486 (1960). 6. E.J. Vandenberg, J. Polym. Sci. A17, 525 (1969).

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

5.

ZUSSMAN ET AL.

Halogenated Polyethers and Polysulfides

71

7. J.S. Shih, J.F. Brandt, M.P. Zussman and D.A. Tirrell, J. Polym. Sci. Polym. Chem. Ed. 20, 2839 (1982). 8. J.S. Shih, Ph.D. Dissertation, Carnegie-Mellon University, 1984. 9. J.S. Shih and D.A. Tirrell, J. Polym. Sci. Polym. Chem. Ed. 22, 781 (1984). 10. J.S. Shih and D.A. Tirrell, J. Macromol. Sci. Chem. A21, 1013 (1984). 11. S. Vaze and D.A. Tirrell, J. Bioactive and Compatible Polym. 1, 79 (1986). 12. D.A. Wicks and D.A. Tirrell, Polym. Prepr. 27(2), 21 (1986). 13. M.P. Zussman and D.A. Tirrell, Macromolecules 14, 1148 (1981). 14. M.P. Zussman and D.A. Tirrell, Polymer Bull. 7, 439 (1982). 15. M.P. Zussman and D.A. Tirrell, J. Polym. Sci. Polym. Chem. Ed. 21, 1417 (1983). 16. M.P. Zussman, Ph.D. dissertation, Carnegie-Mellon University, 1982. 17. M.P. Zussman and D.A in press. 18. R. Bird and C.J.M. Stirling, J. Chem. Soc. Perkin II, 1221, 1973. 19. F.G. Bordwell and W.T. Brannen, Jr., J. Am. Chem. Soc. 86, 4645 (1964). 20. I. Tabushi, Y. Tamaru and Z. Yoshida, Bull. Chem. Soc. Japan 47, 1455 (1974). 21. I. Tabushi, Y. Tamaru, Z. Yoshida and T. Sugimoto, J. Am. Chem. Soc. 97, 2886 (1975). 22. G.H. Schmid and V. Csizmadia, Can. J. Chem. 50, 2465 (1972). 23. R.W. Alder, R. Baker and J.M. Brown, Mechanism in Organic Chemistry, Wiley, New York, 1971, p. 43. 24. A.J. Parker, Chem. Rev. 69, 1 (1969). 25. Y.C. Mac, W.A. Millen, A.J. Parker and D.W. Watts, J. Chem. Soc. (B), 525 (1967). 26. J.P. Kennedy and R.M. Thomas, Makromol. Chem. 53, 28 (1962). 27. J.P. Kennedy in H.F. Mark, N.G. Gaylord and N.M. Bikales, Eds., Encyclopedia of Polymer Science and Technology, Wiley, New York, 1967, Vol. 7, p. 754. RECEIVED

September 11, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 6

Polymeric Dialkylaminopyridines as Supernucleophilic Catalysts 1

1

2

Subhash C. Narang, Susanna Ventura , and Roopram Ramharack 1

SRI International, 333 Ravenswood Avenue, Menlo Park, CA 94025 3M Company, St. Paul, MN 55144 2

Supernucleophilic p lidino)pyridine grou corresponding maleic anhydride copolymers and also by cyclopolymerization of N-4-pyridyl bis(methacryl­ imide). The resulting polymers were examined for their kinetics of quaternization with benzyl chloride and hydrolysis of p-nitrophenylacetate. In both instances, the polymer bound 4-(dialkylamino)pyridine was found to be a superior catalyst than the corresponding low molec­ ular weight analog. 4-(Dimethylamino)pyridine (1, DMAP) and i t s analogs, p a r t i c u l a r l y 4-(pyrrolidino)pyridine (2, PPY) have acquired enormous importance and u t i l i t y as supernucleophilic catalysts i n synthetic organic and polymer chemistry (1_,2) ·

1

2

In 1967, (3) i t was discovered that DMAP catalyzes the benzoylation of m-chloroaniline 10^ times faster than pyridine. This enormous increase i n reaction rate i s unmatched by any other nucleophilic acylation catalyst (3^· I t was shown that the c a t a l y t i c action of DMAP and PPY i s not primarily due to their larger p K s with respect to pyridine, but i s a result of enhanced nucleophilic c a t a l y s i s . f

a

0097-6156/88/0364-0072$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

6.

NARANG ET AL.

73

Diaîkylaminopyridints

+ 9 Il

0

II

R-C-O-C-

I RCOO

NuH

+ RCOOH

C=0 R

The intermediate N-acylpyridinium salt i s highly s t a b i l i z e d by the electron donating a b i l i t y of the dimethylamino group. The increased s t a b i l i t y of the N-acylpyridinium ion has been postulated to lead to increase an easier attack by th provided by the loosely bound carboxylate anion. Dialkylamino pyridines have been shown to be excellent catalysts for acylation (of amines, alcohols, phenols, enolates), t r i t y l a t i o n , s i l y l a t i o n , lactonization, phosphonylation, and carbomylation and as transfer agents of cyano, a r y l s u l f onyl, and a r y l s u l f i n y l groups (l_-3). DMAP has been found to improve the coupling reaction i n s o l i d phase peptide synthesis (A_). Polypeptides synthesized v i a the DMAP-DCC method were found to be of higher purity compared to other methods of synthesis. In polymer chemistry, DMAP has been used for hardening of resins and i n the synthesis of polyurethanes, (5) polycarbonates, (6) and polyphenyleneoxides C7 ) . The tremendous scope of u t i l i z a t i o n of DMAP and PPY as catalysts has led to an active interest i n the development of their polymeric analogs. The pioneering work was carried out by H i e r l et a l (8) and Delaney et a l . (9). They attached 4 - d i a l k y l aminopyridine derivatives to poly(ethyleneimine) and found the modified polymers to be highly active catalysts for hydrolysis of p-nitrophenylcarboxylates. Since then, many research groups have reported the synthesis of polymers functionalized with 4 - d i a l k y l aminopyridine (10-18).

CO

CO

R

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON

74

POLYMERS

EXPERIMENTAL

Materials A l l reagents and chemicals were commercially available materials p u r i f i e d by standard laboratory procedures. N-4-(Pyridyl) Methacrylamide A solution of methacryloyl chloride (44.8 g, 0.43 mol) i n tetrahydrofuran (100 ml) was added dropwise to a s t i r r e d solution of 4-aminopyridine (20 g, 0.21 mol) dissolved i n a two phase system of 10% aq. NaOH (300 ml) and tetrahydrofuran (50 ml) at 1520°C. The reaction mixture was s t i r r e d for 2 hrs. Cone. HC1 was added to the reaction mixture to lower the pH to 8 and the reaction mixture extracte organic extract was drie desired product i n 80% y i e l d . H NMR ( C D C I 3 , TMS) δ 2.05 (s, 3H), 5.6 (s, 1H), 5.9 (s, 1H), 7.8 (m, 2H), 8.6 (m, 2H), 9.6 ppm (s, 1H); IR (KBr) 3200, 3140, 3040, 2980, 1675. 1590, 1510, 1415, 1330, 1290, 1200, 1155, 1000, 940, 860 cm" ; mass spectrum (70 eV) m/e 162 (molecular ion), 147, 134, 119, 93, 78, 69. 1

N-4(Pyridyl) bis(methacrylimide) A solution of N-4-(pyridyl)methacrylamide (27 g, 0.17 mol) i n tetrahydrofuran (250 ml) was added to a s t i r r e d slurry of sodium hydride (8 g of a 60% dispersion i n mineral o i l , 0.2 mol) i n tetrahydrofuran (150 ml) at 15-20°C under a dry nitrogen atmo­ sphere. After s t i r r i n g for 2 hrs, a solution of methacryloyl chloride (21 g, 0.20 mol) i n anhydrous tetrahydrofuran (25 ml) was added dropwise over one hour and the reaction mixture s t i r r e d for another hour. The reaction mixture was quenched by addition of a few ml of methanol. The solvent was evaporated under vacuum and the crude product c r y s t a l l i z e d from ether i n 60% y i e l d , m.p. 113114°C; IR (KBr) 3000, 2980, 1720, 1680, 1635, 1595, 1460, 1355, 1

1310, 1280, 1160 cm" ;

X

H NMR

( C D C I 3 , TMS) δ 2.0 ( s , 6H), 5.6 (d,

4H), 7.1 (m, 2H), 8.7 ppm (m, 2H); 13e NMR(CDC1 ) δ 18.5, 120.9, 122.5, 143.1, 146.6, 150.8, 173.3 ppm, mass spectrum (70 eV) m/e 230 (molecular ion), 229, 202, 189, 187, 174, 161, 145, 78, 70, 69. Anal. Calcd. for C ^ H ^ ^ O o : C 67.8; H 6.1; N 12.2%. Found: C 67.8; H 6.13; N 12.16%. 3

Cyclopolymerization of N-4-(Pyridyl) bis(methacrylimide) N-4-(Pyridyl) bis(methacrylimide) (8.6 g, 37 mmol) was d i s ­ solved i n dimethylformamide (35 ml). The solution was degassed under argon and azobis(isobutyronitrile) (0.4 g, 2 mmol) was added. The reaction mixture was heated to 75°C under argon. After 24 hrs, another portion of AIBN (0.4 g, 2 mmol) was added and the reaction continued for another 24 hrs. The resulting polymer was isolated by p r e c i p i t a t i o n from ether i n 65% y i e l d . DSC of the polymer indicated a Tg at 110°C. TGA showed onset of

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

6.

NARANG ET AL.

75

Diaîkylaminopyridines

decomposition at 400°C under argon. The i n t r i n s i c v i s c o s i t y determined i n chloroform solution at 30°C, was 0.05 d i g " indicating a low molecular weight polymer; UV spectrum i n CH2CI2 showed a λ at 230 nm. IR showed bands at 1790 and 1730 cm" corresponding to the five membered imide ring; *H NMR (CDCI3, TMS) δ 1.24 (s, 6H), 1.70 (s, 4H), 8.24 (broad, 2Η) 8.67 ppm (broad, 2H); C NMR (CDCI3) δ 15.9, 31.1, 50.7, 119.4, 139.2, 150.7, 178.8 ppm. 1

1

1 3

Reduction of Poly(N-4-(pyridyl) bis(methacrylimide)) To a s t i r r e d solution of the polymer (2 g, 17 meq of C=0) i n diglyme (100 ml), boron t r i f l u o r i d e etherate (1.2 ml, 10 mmol) was added under a nitrogen atmosphere. The reaction mixture was cooled to 0°C and a solution of sodium borohydride (1.32 g, 35 mmol) i n diglyme (80 ml) was added dropwise over 30 minutes. The reaction mixture was heated t 70°C fo 16 hr d the quenched with methanol (2-3 ml) and the crude product wa 100 ml). The polymer was f i l t e r e d and the residue washed with water. The polymer was dried i n a vacuum oven at 90°C. The degree of functionalization was 67% as calculated by UV and •'•H NMR spectroscopy. TGA of the pyrrolidinopyrdine polymer showed the onset of weight loss at 350°C under argon. UV λ 261 nm (basic form, CH OH/H 0/NaOH); 281 nm (acidic form, CH o9?S 0/HCl); R NMR (d^-DMSO, TMS) δ 0.95 (broad, 10H), 3.2 (broad, 4H), 6.4 (broad, 2H), 8.1 ppm (broad, 2H); C NMR (d -DMS0) δ 20, 29, 45, 59, 107, 149, 151, 152 ppm. l

3

2

3

2

1 3

6

Kinetics Experimental The quaternization kinetics were followed by NMR spectros­ copy using a JEOL FX-90Q NMR spectrometer. Solvolysis of pj-nitrophenylacetate was followed by UV spectroscopy using a Hewlett Packard 8450 A diode array spectrophotometer. The k i n e t i c s were followed by measuring the increase i n absorbance at 400 nm due to the formation of the p-nitrophenoxide anion i n a t r i s buffer solution at pH 8.5. The substrate was used in excess over the free base catalyst, whose concentration was calculated from spectrophotometry data. Pseudo-first-order rate constants ( k ) determined from the l i n e a r relationship of In (A -A ) with time, were calculated for d i f f e r e n t concentrations of catalyst. A pseudo-first-order rate constant was also calculated for the uncatalyzed hydrolysis at pH 8.5, and was substracted from the values found for the catalyzed hydrolysis. Q b s

œ

t

From the slope of the linear relationship between k ^ and the base concentration, the second-order-rate constants were calculated. 0

s

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

76

CHEMICAL REACTIONS ON POLYMERS

RESULTS AND DISCUSSION We have previously (13) reported a rapid two step synthesis of 4-(pyrrolidino)pyridine copolymers via the reaction of commerc i a l l y available maleic anhydride copolymers with 4-aminopyridine followed by reduction with LiAlH^, yielding polymers with a high degree of f u n c t i o n a l i z a t i o n .

CH—CH-CH -CHC 0=C

/C=0

vX

R

r—\ 2 -

v—/

0

2

H

^ 2

C x

N'

=C u=u. C=0 NN X

y

R

Û

-CH— CH-CH -CH/ \ I

4

0

NN

0

LiAlH

-CH—CH-CH -CH-

C H

2

^

NT

R

In order to determine the e f f i c i e n c y of the polymers as reagents i n nucleophilic c a t a l y s i s , i t was decided to study the rate of quaternization with benzyl chloride. Table I shows the second-order-rate constants for the benzylation reaction i n ethanol. Comparison with DMAP indicates that poly(butadiene-copyrrolidinopyridine) i s the most reactive of a l l the polymers examined and i s even more reactive than the monomeric model. This enhanced r e a c t i v i t y i s probably due to the enhanced hydrophobicity of the polymer chain i n the v i c i n i t y of the reactive s i t e s .

Table I a

KINETICS OF QUATERNIZATION IN ETHAN0L

k_ Nucleophile

1

4-Dimethylaminopyridine

0.0010

Poly(butadiene-co-pyrrolidinopyridine)

0.0014

Poly(methyl v i n y l ether-co-pyrrolidinopyridine)

0.0009

Poly(octadec-l-ene-co-pyrrolidinopyridine)

1

(mol" λ min" )

b

a

The k i n e t i c s were studied at 25.4°C. ^The rate of reaction was too small to measure, presumably because of s t e r i c hindrance due to the long a l k y l chain. Source: Reproduced with permission from Ref. 13. Copyright 1985, Wiley.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

6.

NARANG ET AL.

Diaîkylaminopyridines

77

The d i e l e c t r i c constant of the solvent i n the microenvironment of the polymer chain has been shown to be d i f f e r e n t from that i n the bulk solvent (19). This change i n d i e l e c t r i c constant might enhance the n u c l e o p h i l i c i t y of the pyridine ring and therefore increase the rate of quaternization. The k i n e t i c results are consistent with the observations of Overberger et a l . , (20), who showed that increased hydrophobic nature of the substrate led to faster reaction rates i n nucleophilic c a t a l y s i s . In the present case one would expect the butadiene copolymer to be more hydrophobic than the methylvinylether copolymer. An alternative synthesis of supernucleophilic polymers has been achieved using the following reaction sequence.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

The monomer synthesis and cyclopolymerization were carried out following the procedure of Butler et a l . (21). The r e s u l t i n g polyimide was shown to possess primarily pyrrolidine rings as indicated by infrared spectroscopy (21). I n i t i a l l y , the reduction was carried out with LiAlH^ i n tetrahydrofuran. However, the reaction always led to some overreduction of the pyridine ring. Reduction with BH^/THF was unsuccessful. However, NaBH^/BF3 Et 0 proved to be an excellent reagent for the reduction step, resulting i n the formation of the desired polymer. The polymer was shown by UV and NMR spectroscopy to be 67% functionalized primarily with 4-pyrrolidinopyridine moieties by UV and NMR spectroscopy; according to these data no starting polymer i s present anymore, and the nature of the remaining 23% of func­ t i o n a l i z a t i o n i s unknown. #

2

K i n e t i c Studies. The pioneering work of H i e r l et a l . (8) and Delaney et a l . (9) had phenylcarboxylates was nucleophilic c a t a l y s i s y 4-(dialkylamino) pyridin polymers. Hydrolysis of p-nitrophenylacetate i n a buffer at pH 8.5 showed that the polymer was a s l i g h t l y better catalyst than the monomeric analog PPY (Table I I ) . However, preliminary results indicate that the polymer bound 4-(dialkylamino) pyridine i s more e f f e c t i v e as a catalyst than the monomeric analog i n the hydrolysis of longer carbon chain p-nitrophenylcarboxylates, such as p-nitrophenylcaproate. Figures I and I I show a comparison of the reaction p r o f i l e for PPY and polymer catalyzed hydrolysis for p-nitrophenylacetate and p-nitrophenylcaproate monitored by the appearance of p-nitrophenoxide absorption by UV-VIS spectroscopy. These results confirm the effectiveness of the interactions between the hydro­ phobic polymer chain and the hydrocarbon portion of the substrate, as i t was previously mentioned, i n accordance with the observa­ tions of Overberger et a l (20).

Table II KINETICS OF HYDROLYSIS OF P-NITROPHENYLACETATE AT 25°C _k Nucleophile

(mol"

1

1

λ sec" )

4-Pyrrolidinopyridine

428

Poly(4-pyrrolidinopyridine)

493

Conclusions 4-Pyrrolidinopyridine based polymers react faster with benzyl chloride than low molecular weight analogs. The polymer synthe­ sized by cyclopolymerization of N-4-pyridyl bis(methacrylimide)

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

6.

Dialkylaminopyridines

NARANG ET AL.

0.5

F i g u r e 1.

Absorbance a t 400 nm v s . time f o r t h e p o l y ( 4 - p y r r o l i d i n o p y r i d i n e ) and 4 - p y r r o l i d i n o p y r i d i n e c a t a l y z e d h y d r o ­ l y s i s o f p - n i t r o p h e n y l a c e t a t e a t pH 8.5. 0.5

O.o

ψ 0

1

1

200

•

1

400

•

1

600

·

1

800

•

r

•

1000

1

1200

Time (sec)

F i g u r e 2.

Absorbance a t 400 nm v s . time f o r t h e p o l y ( 4 - p y r r o l i d : n o p y r i d i n e ) and 4 - p y r r o l i d i n o p y r i d i n e c a t a l y z e d hydro l y s i s o f p - n i t r o p h e n y l c a p r o a t e a t pH 8.5.

f o l l o w e d by r e d u c t i o n i s a s u p e r n u c l e o p h i l i c polymer which shows h i g h e r c a t a l y t i c a c t i v i t y compared t o the low m o l e c u l a r weight analogous c a t a l y s t , PPY. Acknowledgment s We a r e g r a t e f u l t o t h e Army Research O f f i c e f o r t h e i r generous support of t h i s work.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

References † 1. 2. 3.

4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21.

Abstracted in part from the Ph.D. thesis of R. Ramharack, submitted to Polytechnic Institute of New York. Hofle, G., Steglich, W. and Vorbruggen, V. Angew. Chem. Int. Ed. Engl. 1978, 17, 569 and references therein. Scriven, E.F.V. Chem. Soc. Rev. 1983, 12, 129 and references therein. (a) Litvinenko, L. M. and Kirichenko, A. I. Dokl, Akad. Nauk, SSSR Ser. Khim., 1967, 176, 97. (b) Steglich, W. and Hofle, G. Angew, Chem. Int. Ed. Engl., 1969, 8, 981. Wang, S. S., Tam, J. P., and Merrifield, R. B. Int. J. Peptide Protein Res., 1981, 18, 459. Wild, J. H. and Tate Jaquiss, D.B.G., Mark 4286 085. Verlaan, J.P.L., Alferink, P.J.T. and Challa, G. J. Mol. Catal., 1984, 24, 235. Hierl, Μ. Α., Gamson, E. P. and Klotz, I. M. J. Am. Chem. Soc., 1979, 101, 6020. Delaney, E. J., Wood, L. E. and Klotz, I. M. J. Am. Chem. Soc., 1982, 104, 799. Shinkai, S., Tsuji, H., Hara, Y. and Manabe, O. Bull. Chem. Soc. Jpn., 1981, 54, 631. Tomoi, M., Akada, Y. and Hakiuchi, H. Makromol. Chem. Rapid Commun., 1982, 3, 537. Guendouz, F., Jacquier, R. and Verducci, J. Tetrahedron. Lett., 1984, 25, 4521. Narang, S. C. and Ramharack, R. J. Polym. Sci. Polym. Lett. Ed., 1985, 23, 147. Mathias, L. J., Vaidya, R. A. and Bloodworth, R. H. J. Polym. Sci. Polym. Lett. Ed., 1985, 23, 289. Storck, W. and Manecke, G. J. Mol. Catal., 1985, 30, 145. Menger, F. M. and McCann, D. J. J. Org. Chem., 1985, 50, 3928. Tomoi, M., Goto, M., Kaikuchi, H. Makromol. Chem. Rapid Commun., 1985, 6, 397. Klotz, I. M., Massil, S. E. and Wood, L. E., J. Polym. Sci., Polym. Chem. Ed., 1985, 23, 575. Mikes, F., Strop P. and Kalal, J. Makromol. Chem, 1984, 175, 2375. Overberger, C. G. and Guterl, A. C. J. Polym. Sci., Polym. Symp., 1978, 62, 13. Butler, G. B. and Myers, Myers J. Macromol. Sci. Chem., 1971, A5, 135, references therein.

RECEIVED November

6, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 7

Styrenic- and Acrylic-Siloxane Block and Graft Copolymers 1

S. D. Smith, G. York, D. W. Dwight , and J . E . McGrath Department of Chemistry and Polymer Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, V A 24061-8699

The synthesis and where the backbones were either acrylic or styrenic with siloxane grafts, were prepared and characterized in order to elucidate the molecular and solid state structures, as well as general physical behavior. Although two microphases could be achieved, the results showed that miscibility (as measured by several techniques) increased with lower graft molecular weights and as the solubility parameters of the backbone were designed to be closer to that of the poly(dimethylsiloxane) (PSX) grafts. An i m p o r t a n t polymer m o d i f i c a t i o n r e a c t i o n i s t h e g r a f t i n g t o o r from a polymer backbone by some c h e m i c a l method t o produce a branched s t r u c t u r e ( 1.). The c h a r a c t e r i z a t i o n of t h e p r o d u c t s of t h e s e r e a c t i o n s i s o f t e n somewhat l e s s w e l l d e f i n e d t h a n b l o c k copolymers (2) due t o t h e c o m p l e x i t y o f t h e m i x t u r e o f p r o d u c t s formed. It is t h e r e f o r e u s e f u l t o p r e p a r e and c h a r a c t e r i z e more w e l l d e f i n e d branched systems as models f o r t h e l e s s w e l l d e f i n e d c o p o l y m e r s . The macromonomer method [3) a l l o w s f o r t h e p r e p a r a t i o n o f more w e l l d e f i n e d copolymers than p r e v i o u s l y a v a i l a b l e . A n i o n i c p o l y m e r i z a t i o n i n s u i t a b l e systems a l l o w s t h e p r e p a r a t i o n of polymers w i t h c o n t r o l l e d m o l e c u l a r weight, narrow m o l e c u l a r weight d i s t r i b u t i o n s and f u n c t i o n a l t e r m i n a t i o n . The f u n c t i o n a l t e r m i n a t i o n of a l i v i n g a n i o n i c p o l y m e r i z a t i o n w i t h a p o l y m e r i z a b l e group has been used f r e q u e n t l y i n t h e p r e p a r a t i o n o f macromonomers ( 4 ) . Our r e s e a r c h has encompassed t h e a n i o n i c homo and b l o c k c o p o l y m e r i z a t i o n s o f D o r hexamethyl c y c l o t r i s i l o x a n e w i t h o r g a n o l i t h i u m s t o p r e p a r e w e l l d e f i n e d p o l y m e r s . As e a r l y a s 1962 PSX macromonomers were r e p o r t e d i n t h e l i t e r a t u r e by Greber (5) b u t the c o p o l y m e r ! z a t i o n o f t h e s e macromonomers d i d n o t become a c c e p t e d t e c h n i q u e u n t i l t h e i r v a l u e was demonstrated by M i l k o v i c h and C u r r e n t address: P.O. Box 160, Sumneytown, P A 18084

0097-6156/88/0364-0085$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

coworkers ( 6 ) . S i n c e t h e n , c o n s i d e r a b l e work has been d e d i c a t e d t o t h e macromonomer t e c h n i q u e i n many l a b o r a t o r i e s around t h e w o r l d . In o u r own r e s e a r c h , t h e f u n c t i o n a l t e r m i n a t i o n of t h e l i v i n g s i l o x a n o l a t e with a c h l o r o s i l a n e f u n c t i o n a l methacrylate leading to s i l o x a n e macromonomers w i t h number average m o l e c u l a r w e i g h t s from 1000 t o 20,000 g/mole has been emphasized. M e t h a c r y l i c and s t y r e n i c monomers were then c o p o l y m e r i z e d w i t h t h e s e macromonomers t o produce g r a f t copolymers where t h e s t y r e n i c o r a c r y l i c monomers comprise t h e backbone, and t h e s i l o x a n e c h a i n s a r e pendant as g r a f t s as d e p i c t e d i n Scheme 1. Copolymers were p r e p a r e d w i t h s i l o x a n e c o n t e n t s from 5 to 50 w e i g h t p e r c e n t .

Scheme 1, ΡΜΠΑ

ΑΛΛΛ/ννννννννννΛΛΛ

PSX

PSX

PSX

The i n i t i a t i o n o f t h e c y c l i c s i l o x a n e monomers w i t h a l i v i n g p o l y m e r i c l i t h i u m s p e c i e s such as p o l y s t y r y l l i t h i u m l e a d s t o b l o c k c o p o l y m e r s , as o u t l i n e d i n Scheme 2, were a l s o of i n t e r e s t . These s t y r e n i c - s i l o x a n e b l o c k copolymers were p r e p a r e d w i t h s i l o x a n e c o n t e n t s from 10 t o 50 w e i g h t p e r c e n t .

Scheme 2.

3

(CH 0

2

CH)T

ι

A

3

,' Ϊ lAAAAAÎSi-OÎ^^Si-CHj.

II

D

CH.

I

CH,

R= H, C H , t-C^Hg 3

R e c e n t l y , the importance of i n c o r p o r a t i n g s i l i c o n c o n t a i n i n g segments i n t o copolymers has become i n c r e a s i n g l y w e l l a p p r e c i a t e d . The d e s i r a b l e p r o p e r t i e s o f s i l i c o n i n c l u d e i o n e t c h r e s i s t a n c e f o r m i c r o l i t h o g r a p h y ( 2 * 8 ) , and h i g h e r oxygen p e r m e a b i l i t y i n membrane m a t e r i a l s ( 9 ) , as w e l l as b i o c o m p a t a b i l i t y . u n f o r t u n a t e l y , homo- o r random copolymers of p o l y s i l o x a n e s o f t e n have Tg's t o o low t o be u s e f u l as f i l m f o r m i n g m a t e r i a l s . In c o n t r a s t , t h e phase s e p a r a t i o n of t h e s e g r a f t and b l o c k m a t e r i a l s d i s c u s s e d i n t h i s paper a l l o w t h e i n c o r p o r a t i o n of s i l i c o n moieties at r e l a t i v e l y high l e v e l s while

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

7.

Styrenic- and Acrylic-Siloxane

SMITH ET AL.

Copolymers

87

m a i n t a i n i n g the s o l u b i l i t y and i n t e g r i t y of t h e g l a s s y polymer phase. A l l o y s o f t h e s e m u l t i p h a s e copolymers a r e a l s o b e i n g i n v e s t i g a t e d . Experimental Cyclohexane ( P h i l l i p s 99+ mole %) was p u r i f i e d by s t i r r i n g o v e r 2 4 e from a sodium d i s p e r s i o n . Tetrahydrofuran ( F i s h e r ) was d i s t i l l e d from a sodium/benzophenone complex. T o l u e n e ( F i s h e r ) was degassed t h o r o u g h l y and used d i r e c t l y i n radical polymerizations. ( P e t r a r c h ) was p u r i f i e d by m e l t i n g and s t i r r i n g i n the p r e s e n c e o f f i n e l y d i v i d e d c a l c i u m h y d r i d e t h e n sublimed under vacuum. The was then d i s s o l v e d i n p u r i f i e d c y c l o h e x a n e and s t o r e d under N_. S t y r e n e ( F i s h e r ) , p - m e t h y l s t y r e n e ( M o b i l ) , and t - b u t y l s t y r e n e (DOW) were p u r i f i e d by p a s s i n g through a column of a c t i v a t e d alumina an t r a c e s o f 0^. Further p u r i f i c a t i o d i b u t y l magnesium r e s u l t e M e t h a c r y l a t e monomers were d i s t i l l e d from c a l c i u m h y d r i d e and s t o r e d i n a f r e e z e r u n t i l use. Macromonomers were p r e p a r e d by i n i t i a t i o n of the D i n c y c l o h e x a n e w i t h s - B u L i a f t e r which p u r i f i e d t e t r a h y d r o t u r a n was added t o promote p r o p a g a t i o n of the s i l o x a n o l a t e s p e c i e s . Termination with 3-methacryloxypropyl d i m e t h y l c h l o r o s i l a n e ( P e t r a r c h , Inc.) a f f o r d e d the macromonomer i n h i g h y i e l d s which was t h e n p r e c i p i t a t e d i n methanol and d r i e d under vacuum. Macromonomers were a n a l y z e d by s e v e r a l t e c h n i q u e s t o c o n f i r m not o n l y t h e i r m o l e c u l a r weight and m o l e c u l a r weight d i s t r i b u t i o n but a l s o t h e i r m e t h a c r y l a t e end group functionality. Vapor phase osmometry (VPO), run i n t o l u e n e u s i n g s u c r o s e o c t a c e t a t e as a s t a n d a r d , was used as a method f o r d e t e r m i n a t i o n of number average m o l e c u l a r w e i g h t . NMR a n a l y s i s (IBM 270 MHz SL i n s t r u m e n t ) a l l o w e d a r a t i o i n g of a l p h a methyl p r o t o n s on t h e m e t h a c r y l a t e group t o the s i l i c o n m e t h y l s as a d e t e r m i n a t i o n of f u n c t i o n a l i t y . NMR was not s u f f i c i e n t l y p r e c i s e f o r m o l e c u l a r weights above a p p r o x i m a t e l y 2000 and a n o t h e r t e c h n i q u e based on the UV a n a l y s i s of the m e t h a c r y l a t e f u n c t i o n a l i t y was d e v e l o p e d . UV s p e c t r a run on a P e r k i n Elmer 552 i n s t r u m e n t (scanned from 350 nm t o 190 nm a t 20 nm/minute) e s t a b l i s h e d a wavelength maximum a t 214 nm f o r t h e c a r b o n y l group of our m e t h a c r y l a t e f u n c t i o n a l endgroup ( F i g u r e 1 ) . Then, absorbance measurements were determined a t 214 nm and a c a l i b r a t i o n p l o t u s i n g B e e r s law w i t h methyl m e t h a c r y l a t e as a s t a n d a r d i n THF was p r e p a r e d . The end group a n a l y s i s of known macromonomer c o n c e n t r a t i o n s t h u s was used t o e s t a b l i s h the f u n c t i o n a l i t y . F r e e r a d i c a l c o p o l y m e r i z a t i o n s o f the a l k y l m e t h a c r y l a t e s were c a r r i e d out i n t o l u e n e a t 60°C w i t h 0.1 weight p e r c e n t (based on monomer) AIBN i n i t i a t o r , w h i l e t h e s t y r e n i c systems were p o l y m e r i z e d i n c y c l o h e x a n e . The s o l v e n t c h o i c e s were p r i m a r i l y based on systems which would be homogeneous but a l s o show low c h a i n t r a n s f e r c o n s t a n t s . M e t h a c r y l a t e p o l y m e r i z a t i o n s were c a r r i e d out a t 20 w e i g h t p e r c e n t s o l i d s H

S 0

t

h

e

n

d

i

s

t

i

l

l

d

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

and t h e s t y r e n i c systems were s t a r t e d a t 50 weight p e r c e n t s o l i d s then d i l u t e d w i t h time t o p r e v e n t s o l i d i f i c a t i o n o f t h e mixture. Copolymers a f t e r workup were e x t r a c t e d e x t e n s i v e l y w i t h hexanes o r i s o p r o p a n o l , depending on polymer s o l u b i l i t y , t o remove any p o l y s i l o x a n e homopolymer. Under a p p r o p r i a t e c o n d i t i o n s , t h e s e amounts were q u i t e low. The a n i o n i c p o l y m e r i z a t i o n o f t h e s t y r e n e monomers was c o n d u c t e d a t -78°C i n THF w i t h s-BuLi as t h e i n i t i a t o r . The second b l o c k was p r e p a r e d by a d d i n g t o t h i s l i v i n g polymer a c a l c u l a t e d amount o f D^/cyclohexane m i x t u r e . S i l o x a n o l a t e i n i t i a t i o n was e v i d e n c e d by l o s s o f t h e c h a r a c t e r i s t i c orange c o l o r o f t h e l i v i n g s t y r e n e a n i o n . The r e a c t i o n was a l l o w e d t o warm t o room temperature and g i v e n adequate time (5-20 hours) f o r p r o p a g a t i o n t o near q u a n t i t a t i v e c o n v e r s i o n . Termination was a c h i e v e d by r e a c t i o n w i t h t r i m e t h y l c h l o r o s i l a n e i n s l i g h t molar e x c e s s a t room t e m p e r a t u r e . The copolymers were then p r e c i p i t a t e d , d r i e d and homopolymer. GPC i n d i c a t e d i s t r i b u t i o n f o r these copolymer f r e e of s t y r e n i c homopolymer. T y p i c a l number average m o l e c u l a r weights p r e p a r e d were 100-150,000 f o r t h e f i r s t b l o c k . The p o l y s i l o x a n e c o n s t i t u t e d 10 t o 60 weight p e r c e n t o f t h e o v e r a l l copolymers. Thus, t h e t o t a l m o l e c u l a r w e i g h t was as h i g h as 300,000 gm/mole. V i s c o s i t i e s become v e r y h i g h and must be c o n t r o l l e d t o keep t h e m o l e c u l a r weight d i s t r i b u t i o n s from broadening. Polymers were a n a l y z e d by G e l Permeation Chromatography (GPC) w i t h a Waters 150-Ç GPC f i t t e d w i t h m i c r o s t y r a g e l columns o f 500Â, 10 , 10 , 10 , and 10 Â p o r o s i t i e s i n THF. P o l y ( m e t h y l m e t h a c r y l a t e ) (PMMA) and p o l y s t y r e n e s t a n d a r d s ( P o l y s c i e n c e s ) were g e n e r a l l y used t o e s t i m a t e number average molecular weights. Number average m o l e c u l a r w e i g h t s o f g r e a t e r than 150,000 were d e s i r e d f o r o p t i m a l polymer p r o p e r t i e s . NMR s p e c t r a on an IBM 270 MHz SL i n s t r u m e n t were used t o determine t h e s i l o x a n e i n c o r p o r a t i o n i n t o t h e copolymer. FTIR s p e c t r a were r u n on a N i c o l e t MX-1 s p e c t r o p h o t o m e t e r . D i f f e r e n t i a l S c a n n i n g C a l o r i m e t e r (DSC) thermograms were o b t a i n e d on a P e r k i n Elmer DSC-2 r u n a t 10°C p e r minutes. Dynamic M e c h a n i c a l Thermal A n a l y s i s (DMTA) s p e c t r a were o b t a i n e d on a Polymer Labs DMTA a t a f r e q u e n c y o f 1Hz w i t h a temperature range from -150°C t o +150°C a t a scan r a t e o f 5°C per m i n u t e . C o n t a c t a n g l e measurements were o b t a i n e d u s i n g a goniometer, measuring t h e a d v a n c i n g a n g l e from 2 t o 20 m i c r o l i t e r drop s i z e s , o f p u r i f i e d water upon polymer f i l m s a t room temperature. F i l m s were c a s t on m e t a l p l a t e s and a l l o w e d t o d r y s l o w l y from c h l o r o f o r m s o l u t i o n s . S e v e r a l s p o t s were measured on each f i l m and t h e r e s u l t s a v e r a g e d . ESCA s p e c t r a were o b t a i n e d w i t h a K r a t o s XSAM -800 i n s t r u m e n t w i t h Mg anode 200 watts under a vacuum o f 10-9 t o r r . TEM a n a l y s i s was done on a P h i l l i p s I L 420 Τ STEM a t 100 KV i n t h e TEM mode. M o r p h o l o g i c a l s t u d i e s were conducted on model copolymers c o n t a i n i n g a methyl m e t h a c r y l a t e backbone and a p p r o x i m a t e l y

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

SMITH ET AL.

Styrenic- and Acrylic-Siloxane

Copolymers

MAX. = 0.605 AT 214 nm.

CONC. = 0.210 g / l i t e r

'

210

1

250

290

1

330

WAVELENGTH (nm) F i g u r e 1. UV spectrum o f m e t h a c r y l a t e f u n c t i o n a l PSX macromonomer w i t h M 1600.

η

(A)

(Β)

A

1 t • ι *—Γ 25

30

ι

ι ι I I I

25

30

E l u t i o n Volume (ml) F i g u r e 2. S i z e e x c l u s i o n chromatograms of p o l y s t y r e n e (A) and p ( t - b u t y l s t y r e n e ) - b - P S X ( B ) .

standard

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

90

CHEMICAL REACTIONS ON POLYMERS

5,000, 10,000 and 20,000 m o l e c u l a r weight (Mn) p o l y d i m e t h y l s i l o x a n e s i d e c h a i n s . The weight f r a c t i o n of s i l o x a n e was h e l d a p p r o x i m a t e l y c o n s t a n t a t 20% and 50%. T h i n ( a p p r o x i m a t e l y 100 nm) f i l m s were c a s t on water and t h i c k ( a p p r o x i m a t e l y 1 mm) f i l m s were c a s t on s t a i n l e s s s t e e l . Specimens from t h e l a t t e r f i l m s were microtomed a t c r y o s c o p i c t e m p e r a t u r e s . R e s u l t s and D i s c u s s i o n The p r e p a r a t i o n of m e t h a c r y l a t e f u n c t i o n a l p o l y d i m e t h y l s i l o x a n e (10,11,12) o f h i g h f u n c t i o n a l i t y v i a E q u a t i o n 1 was an

CH. THF R L i + D^

CH.

0 CH.

I I II I I I + I " • R-(-Si-O-)Li + C l - S i - ( C H ^ ) -Q-C-C=CH_ *2'3 " 2 CH

CH

3

0 CH.

I

(1)

|_o-c-C=CH,

important f i r s t step i n the p r e p a r a t i o n of the w e l l defined g r a f t copolymers. The macromonomers p r e p a r e d were c h a r a c t e r i z e d f o r number average m o l e c u l a r weights v i a VPO. The f u n c t i o n a l i t y o f t h e end groups were a l s o determined by NMR o r UV a n a l y s i s which s h o u l d p r o v i d e i d e n t i c a l m o l e c u l a r weights f o r p e r f e c t l y m o n o f u n c t i o n a l m a t e r i a l s . As can be seen i n T a b l e I , a good c o r r e s p o n d e n c e was o b t a i n e d . I n c o r p o r a t i o n of the macromonomers i n t o copolymers v i a f r e e r a d i c a l c o p o l y m e r i z a t i o n can a l s o be used as a check on f u n c t i o n a l i t y s i n c e n o n f u n c t i o n a l m a t e r i a l s o b v i o u s l y w i l l n o t be incorporated. P r o t o n NMR was used t o c o n f i r m t h e amount o f PSX

T a b l e I . Mn V a l u e s of M e t h a c r y l a t e F u n c t i o n a l Poly(Dimethyl Siloxane) v i a Spectroscopic and Osmotic Techniques u

SAMPLE 1 2 3

1H NMR* 1600 0900

VPO 6500 1500 1030

uv

6000 1700 0900

Comparison o f s i l i c o n m e t h y l / a c r y l a t e methyl Solvent: Toluene From e s t e r c a r b o n y l a t absorbance 214 nm (UV)

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

7.

SMITH ET AL.

Styrenic- and Acrylic-Siloxane

Copolymers

i n c o r p o r a t i o n ( T a b l e s I I and I I I ) i n t o the c o p o l y m e r s . In g e n e r a l , the i n c o r p o r a t e d amounts a r e r e l a t i v e l y c l o s e t o the charged amounts, i n d i c a t i n g b o t h h i g h macromonomer f u n c t i o n a l i t y and a p p r o p r i a t e c o p o l y m e r i z a t i o n c o n d i t i o n s .

T a b l e I I . NMR A n a l y s i s of P o l y ( D i m e t h y l S i l o x a n e ) Content i n S t y r e n i c G r a f t and B l o c k Copolymers Sample D e s c r i p t i o n Grafts; Ρ(Styrene)-g-PSX P(p-Methyl Styrene)-g-PSX P ( t - B u t y l Styrene)-g-PSX

Charged 30 10 20

Blocks: Ρ(Styrene)-b-PSX P(p-Methyl S t y r e n e ) - b - P S P ( t - B u t y l Styrene)-b-PS P ( t - B u t y l Styrene)-b-PSX

Found 27 9 20

2

40

42

T a b l e I I I . I n f l u e n c e of S i l o x a n e Content and M o l e c u l a r Weight on the Water C o n t a c t A n g l e s of P o l y ( M e t h y l M e t h a c r y l a t e ) - P o l y ( D i m e t h y l S i l o x a n e ) G r a f t Copolymers Macro Monomer M

Weight % Charged

PMMA Homopolymer C o n t r o l 5 1,000 10 15 20 5,000

10,000

20,000

Weight % via NMR

4.0 7.6 9.0 15.0

Contact Angle 74° 97°

105° 99°

5 10 15 20

4.3 6.8 12.4 16.8

5 10 15 20

5.8 9.6 14.0 15.9

108°

5 10 20

4.0 7.0 12.0

109°

107°

109°

109°

Copolymer work-up i n c l u d e d e x t r a c t i o n w i t h hexane t o remove any p o l y s i l o x a n e homopolymer.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON

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Very w e l l d e f i n e d b l o c k copolymers of s t y r e n e , p-methyl s t y r e n e , p - t e r t - b u t y l s t y r e n e and PSX were p r e p a r e d , as judged by GPC, w i t h m o l e c u l a r weights o f over 100,000 g/mole. I m p u r i t y l e v e l s a t t h i s m o l e c u l a r weight become e x t r e m e l y c r i t i c a l and c a r e f u l vacuum t e c h n i q u e s must be used where appropriate t o exclude a l l contaminations. As mentioned e a r l i e r , t h e g r a f t m o l e c u l a r weight and copolymer c o m p o s i t i o n s d i c t a t e the p r o p e r t i e s o f t h e system. DSC measurements i n d i c a t e p a r t i a l phase m i x i n g f o r low m o l e c u l a r weight g r a f t s , a s e v i d e n c e d by a s h i f t i n g o f the Tg of PMMA t o lower temperatures ( T a b l e I V ) . A l t h o u g h the Tg o f the p o l y m e t h y l m e t h a c r y l a t e systems w i t h g r a f t m o l e c u l a r weights of 5K, 10K and 20K a r e r o u g h l y e q u i v a l e n t , changes i n t h e b r e a d t h o f the t r a n s i t i o n i n d i c a t e d i f f e r e n c e s i n the phase m i x i n g , which i s t o be e x p e c t e d . S i m i l a r r e s u l t s are observed by Dynamic M e c h a n i c a l Thermal A n a l y s i s ( F i g u r e 3, T a b l e I V ) .

T a b l e IV. Influenc on G l a s s T r a n s i t i o n Temperature f o r PMMA-g-PSX Copolymers (~16 wt.% PSX) Macronomer Mn 1000 5000 10000 20000 C o n t r o l PMMA determined

Tq by DSC (°C) 111 123 125 127 127

by M e c h a n i c a l Loss P l o t

Λ

β

Tq by ϋ Μ Τ Α ( Ο 110 123 126

(1 Hz)

S i n c e p o l y ( d i m e t h y l s i l o x a n e ) i s w e l l known t o d i s p l a y a low s u r f a c e energy, i t was e x p e c t e d t o dominate t h e s u r f a c e o f the microphase s e p a r a t e d copolymers. Contact angle a n a l y s i s i n d e e d i n d i c a t e d a change i n s u r f a c e c o m p o s i t i o n w i t h m o l e c u l a r weight and c o m p o s i t i o n o f t h e g r a f t s . Copolymers c o n t a i n i n g h i g h e r m o l e c u l a r weight g r a f t s , which a r e b e l i e v e d t o phase s e p a r a t e t o a h i g h e r e x t e n t , have h i g h e r c o n t a c t a n g l e s due t o the p r e s e n c e o f the h i g h e r c o n c e n t r a t i o n o f the p o l y s i l o x a n e a t the s u r f a c e ( T a b l e I I I ) . T h i s agrees w i t h s e v e r a l r e s u l t s from our l a b o r a t o r y and elsewhere (1^3). A g a i n t h e 5000 mw g r a f t system does n o t dominate t h e s u r f a c e a t low p e r c e n t s i l o x a n e t o t h e same e x t e n t , i n d i c a t i n g a p a r t i a l phase m i x i n g . ESCA was used as a t o o l t o q u a n t i f y the s u r f a c e c o m p o s i t i o n . Through t h e use o f a n g u l a r dependent depth p r o f i l i n g the d o m i n a t i o n o f the s u r f a c e was o b s e r v e d t o be g r e a t e r f o r h i g h e r m o l e c u l a r weight g r a f t s . I t i s noteworthy t o p o i n t o u t t h a t h i g h e r a n g l e s p e n e t r a t e deeper i n t o t h e s u r f a c e and as an a p p r o x i m a t i o n , an a n g l e o f 10 degrees measures about the t o p 510Â o f t h e s u r f a c e , w h i l e the 90 degree measurement i n d i c a t e s t h e c o m p o s i t i o n over t h e t o p 60 Â . Another f a c t o r i s t h a t the number o f e l e c t r o n s e s c a p i n g f o l l o w s an i n v e r s e e x p o n e n t i a l r e l a t i o n s h i p w i t h d e p t h , so t h a t s u r f a c e c o m p o s i t i o n has a

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

7.

Styrenic- and Acrylic-Siloxane

SMITH ET AL.

Copolymers

l a r g e e f f e c t on even t h e l a r g e a n g l e s . I n T a b l e V we can see t h e t r e n d s i n c o m p o s i t i o n w i t h g r a f t m o l e c u l a r weight and

T a b l e V. I n f l u e n c e o f S i l o x a n e G r a f t M o l e c u l a r Weight and Composition on S u r f a c e C o m p o s i t i o n o f PMMA-g-PSX Copolymers by V a r i a b l e A n g l e XPS (ESCA) (Copolymers ~5 wt.% PSX) % Poly(Dimethyl Siloxane) Detected 30° 90° 10°

E x i t Angle Macromonomer Mn

1000 5000 10000 20000

52 86 97 100

79 86 100 100

41 69 72 90

depth. I n o u r s t y r e n i c b l o c k copolymers, t y p i c a l PSX b l o c k m o l e c u l a r weights were g r e a t e r than 10K and h i g h s u r f a c e c o n c e n t r a t i o n s o f PSX were a g a i n o b s e r v e d . R e s u l t s from t h e s t y r e n i c b l o c k and g r a f t copolymers a r e somewhat s i m i l a r and are presented i n Table V I .

Table VI. ESCA Study o f S t y r e n i c - S i l o x a n e B l o c k and G r a f t Copolymers (Copolymer C o m p o s i t i o n ~10 wt.% PSX) % PSX

10°

30°

90°

Copolymer Ρ(Styrene)-b-PSX Ρ(Styrene)-g-PSX IK

91 79

80 52

52 32

P(p-Methyl

48

20

12

82 39

56 24

40 29

Angle

S t y r e n e ) - g - P S X IK

P ( t - B u t y l Styrene)-b-PSX P ( t - B u t y l S t y r e n e ) - q - P S X IK

From T r a n s m i s s i o n E l e c t r o n M i c r o s c o p y (TEM), t h e morphology o f t h e p o l y ( m e t h y l m e t h a c r y l a t e ) g r a f t system changed s i g n i f i c a n t l y as a f u n c t i o n o f a r c h i t e c t u r e and c o m p o s i t i o n ( F i g u r e 4). The average domain s i z e s v a r y from 12 nm f o r t h e 5K g r a f t s t o 21 nm f o r t h e 20K g r a f t s , w h i l e t h e IK g r a f t systems showed no a p p a r e n t phase s e p a r a t i o n . F u r t h e r d e t a i l s o f t h i s i n t e r e s t i n g morphology w i l l be r e p o r t e d l a t e r . However, i t i s a l r e a d y c l e a r t h a t remarkably w e l l d e f i n e d s o l i d s t a t e g r a f t s t r u c t u r e s c a n be d e v e l o p e d . As a comparison t o t h e TEM measurements o f domain s i z e , S m a l l A n g l e X-ray s c a t t e r i n g (SAXS) ( c o u r t e s y o f P r o f . G. L. W i l k e s ) was a l s o r u n on t h e PMMA-g-PSX copolymers ( T a b l e V I I ) . Two t r e n d s a r e

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

μ 1.6

Y 1.2

0.8

0.4

-130

-70 TEMPERATURE °C

Figure 3. Dynamic mechanical behavior of PMMA-g-PSX copolymer: 20 wt.% siloxane of M 10 000. η f

5K

10K

2 OK

Figure 4. Comparison of the morphologies of PMMA-g-PSX (16 wt.% PSX) of 5000, 10000 and 20000 g/mole siloxane grafts by TEM.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

H W ξ H

7.

Styrenic- and Acrylic-Siloxane

SMITH ET AL.

Copolymers

T a b l e V I I . Comparison of S m a l l A n g l e X-Ray A n a l y s i s o f PMMA-g-PSX Copolymers w i t h TEM Domain S i z e Data (Copolymers ~16 wt.% PSX) Macromonomer Mn 1000 5000 10000 20000

Domain S i z e (TEM) 8 nm. 15 nm. 20 nm.

Interdomain Spacing 12.4 nm. 18.8 nm. 28.6 nm. 37.6 nm.

Max. S c a t t e r i n g Intensity 30 110 260 540

a p p a r e n t , one b e i n g t h a t t h e r e i s a c o r r e s p o n d i n g i n c r e a s e i n interdomain spacing with g r a f t molecular weight. The o t h e r t r e n d i s t h a t the n o r m a l i z e d s c a t t e r i n g i n t e n s i t y a l s o v a r i e s w i t h g r a f t m o l e c u l a r weight, i n d i c a t i n g t h a t ^ b e t t e r phase separation i s occurring a leas u n t i l 10 g/mole Als SAXS c o n f i r m s t h a t even a t h e r e i s a phase s e p a r a t i o phase d e f i n i t i o n i s p r o b a b l y t o o weak t o be d e f i n e d i n t h e TEM technique. F u r t h e r a n a l y s i s of t h e s e phenomena w i l l be reported i n forthcoming papers. S i m i l a r s t u d i e s were u n d e r t a k e n as a comparison i n t h e s t y r e n i c systems, a l t h o u g h i n t h e s e systems we a l s o were a b l e t o compare t h e g r a f t systems t o d i b l o c k systems of s i m i l a r composition. DSC a l s o shows a d e p r e s s i o n o f the h i g h temperature Tg f o r a l l of t h e s t y r e n e s f o r the IK g r a f t systems. The 5K systems showed a s m a l l e r d e p r e s s i o n b u t s t i l l a s l i g h t l o w e r i n g o f t h e Tg ( T a b l e V I I I ) . C l e a r l y , the t b u t y l s t y r e n e system i s most i n f l u e n c e d , as a n t i c i p a t e d .

Table V I I I . Dependence of A r c h i t e c t u r e and M o l e c u l a r Weight o f S t y r e n i c - S i l o x a n e B l o c k and G r a f t Copolymers on Tg (Copolymers ~20 wt.% PSX) Copolymer Type Ρ(Styrene)-b-PSX Ρ(Styrene)-g-PSX Ρ(Styrene)-g-PSX Ρ(Styrene)-g-PSX P(p-Methyl P(p-Methyl P(p-Methyl P(p-Methyl

Tg IK 5K 10K

Styrene)-b-PSX Styrene)-g-PSX IK S t y r e n e ) - g - P S X 5K Styrene)-g-PSX 10K

P ( t - B u t y l Styrene)-b-PSX P ( t - B u t y l Styrene)-g-PSX IK P ( t - B u t y l Styrene)-g-PSX 5K P ( t - B u t y l S t y r e n e ) - g - P S X 10K B l o c k Copolymers a r e of ~100K-20K weights and a r e d i b l o c k s .

(DSC), °C 106 74 100 103 115 80 107 110 149 100 139 143

block molecular

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96

CHEMICAL REACTIONS ON POLYMERS

ESCA a n a l y s i s showed a s i m i l a r t r e n d o f i n c o m p l e t e s u r f a c e c o v e r a g e f o r t h e IK systems. A l s o , no domains were v i s i b l e i n any o f t h e IK s t y r e n i c g r a f t systems by TEM. T h e r e i s an e x p e c t e d t r e n d w i t h r e s p e c t t o s o l u b i l i t y parameter, p ( t - b u t y l s t y r e n e ) (δ 8.1) has a s o l u b i l i t y parameter much c l o s e r t o t h a t o f p o l y d i m e t h y l s i l o x a n e (δ 7.3) t h a n does p(p-methyl s t y r e n e ) which i s c l o s e r than ρ(styrene) (δ 9.1). P r e l i m i n a r y d a t a does i n d i c a t e t h a t f o r a copolymer of s i m i l a r c o m p o s i t i o n t h e ρ(t-butylstyrene) polymer has s m a l l e r domains and, i n g e n e r a l , a p a r t i a l l y phase mixed s u r f a c e and s o l i d state structure. s

s

s

Conclusions The macromonomer t e c h n i q u e p r o v i d e s t h e p o s s i b i l i t y o f p r e p a r i n g g r a f t copolymers o f copolymers n o t s y n t h e t i c a l l y p o s s i b l e p r e v i o u s l y . Th u s e f u l n e s f th t e c h n i q u e was d e m o n s t r a t e the a c r y l i c - s i l o x a n e an p r e p a r e d by t h i s t e c h n i q u e were r e p o r t e d . Complimentary v e r y w e l l d e f i n e d b l o c k copolymers o f s t y r e n e , p-methyl s t y r e n e and p - t e r t - b u t y l s t y r e n e w i t h p o l y d i m e t h y l s i l o x a n e were a l s o prepared. P r e l i m i n a r y c h a r a c t e r i z a t i o n shows t h a t b l o c k l e n g t h s and c o m p o s i t i o n s were c l o s e t o t h e d e s i r e d v a l u e s and t h a t narrow m o l e c u l a r w e i g h t d i s t r i b u t i o n s were a c h i e v e d . We have i l l u s t r a t e d t h e u t i l i t y o f t h e t e c h n i q u e and shown t h e need f o r f u r t h e r i n v e s t i g a t i o n s which a r e c o n t i n u i n g i n o u r laboratories.

Literature Cited 1. Battaerd, H.; Tregear, G. W. Graft Copolymers; Wiley: New York, 1967. 2. Noshay, Α.; McGrath, J. E. Block Copolymers: Overview and Critical Survey; Academic Press: New York, 1977. 3. Milkovich, R. In Anionic Polymerization: Kinetics, Mechanisms and Synthesis; ACS Symposium Series No. 166; American Chemical Society: Washington, DC, 1981. 4. Rempp, P.; Lutz, P.; Masson, P.; Franta, E. Makromol. Chem. 1984, Suppl. 8, 3. 5. Greber, G.; Reese, E. Makromol. Chem. 1962, 55, 96. 6. Milkovich, R.; Chiang, M. U.S. Patent 3 786 116, 1974. 7. Reichmanis, E.; Smolinsky, G. J. Electrochem. Soc.: Solid State Science and Tech., 1985, 132, 1178. 8. Bowden, M.; et al. PMSE Preprints, ACS Anaheim, September 1986. 9. Kawakami, Y.; Aoki, T.; Hisada, H.; Yamamura, Y.; Yamashita, Y. Polymer Comm., 1985, 26(5), 133. 10. Rempp, P.; Franta, E. Advances in Polymer Science, 1984 58. 11. Kawakami, Y.; Yamashita, Y. In Ring Opening Polymerization, Kinetics, Mechanisms and Synthesis; McGrath, J. E., Ed.; ACS 286, 1985, Chapter 19. 12. Cameron, G. G.; Chisholm, M. S. Polymer, 1985, 26, 437. 13. Gaines Jr., G. L. Macromolecules, 1981, 14, 208. RECEIVED

August 27,

1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 8

Effect of the Polymer Backbone on the Thermotropic Behavior of Side-Chain Liquid Crystalline Polymers Coleen Pugh and Virgil Percec Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44106

Poly(epichlorohydrin) (PECH) and poly(2,6 - dimethyl1,4-phenylene oxide mesogenic units separate spacers of zero to ten methylene units were synthesized and characterized in order to test the "spacer concept." Both polymers were modified by phase transfer catalyzed esterifications of the chloromethyl groups (PECH) or the bromobenzyl groups (brominated PPO) with potassium ω-(4-oxybiphenyl) alkanoates and potassium ω-(4-methoxy-4-'oxybiphenyl)alkanoates. While PPO required ten methylene units as a spacer and 4,4'-methoxybiphenyl as mesogen to present thermotropic liquid crystalline mesomorphism, PECH required no spacer. Since Finkelmann and Ringsdorf introduced the spacer concept, i t has been well accepted that a requirement for obtaining thermotropic side-chain l i q u i d c r y s t a l l i n e polymers i s that a f l e x i b l e spacer must be introduced to p a r t i a l l y decouple the mobility of the main chain from that of the mesogenic groups (1-4). Without a spacer, mesophase formation would require that the polymer backbone be s i g n i f i c a n t l y distorted from i t s normal random c o i l conformation. At the same time, the backbone imposes a s t e r i c hindrance on the packing of the mesogens. For this reason, most polymers with the mesogenic groups d i r e c t l y attached to the backbone are amorphous (_5). There are however several exceptions to this rule, most of which are l i s t e d i n Table I, together with their phase transitions. Why i s this? I t must certainly be true that the motions of the mesogen must be decoupled from those of a r i g i d polymer backbone. But what about very f l e x i b l e polymer backbones? We propose that such a backbone may i t s e l f act as a f l e x i b l e spacer. Table I demonstrates that most l i q u i d c r y s t a l l i n e polymers lacking a spacer are formed from a f l e x i b l e polyacrylate backbone. In contrast, the methyl substituent i n polymethacrylate backbones both reduce main chain mobility and imposes additional s t e r i c barriers to mesophase formation. Therefore, successful l i q u i d c r y s t a l l i n e formation of polymethacrylates has been achieved only 0097-6156/88/0364-0097$06.50/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

98

CHEMICAL REACTIONS ON POLYMERS

Table I . Polymers with Direct Attachment of Mesogens

Polymer

Phase Transitions

-CH -ÇH— 2

-CH -ÇH—

_

2

_

Reference

S 285 I

7-11

S 205 I

7.8

S 270 I S 303 I

12 12

S 240 I

12

S 232 I

12

Κ 88.3 Ν 120.6 I

13

—CH2-CH-

>-cx—

^-°-\>0·

X - H X - H

Κ

R - CN R - C H 5

Χ - CH

3

R - CN

Χ - CH

3

R - c H

n

5

_CH->-CH—

N

R - 0C H 4

9

R - 0C H 6

1 3

R - CN Χ - H -CH-CX-

ο

X - CH

O-Lo-O-OÎ-r^-OR

™—*

—*

R - C

C H

R

3

3

-CHz-^X—

X - H

°*-0-O-CH=N-O-R w

w

-CHjr-ÇX-

Χ - H X - CH

X - CH -CH^X0270 I

5

R - 0C H

n

S >270 I

5

3

5

3

14

S 270 I

R - C00H R - C00H

3

13

Κ 113.8 Ν 140.5 î S 200 I

3 3

9

" 9 19 R - C H η f» IJ R - C H C

R -

χ - CH

û4-0-^^t**N-Q-R

H

4

" 3 X - CH \t /»ιι X - CH

X

1 6

R- C H

3

Κ 94.5 S 97.7 Ν 116 I

5

Κ 125.8 I (124.8 C 91 K) 17 Κ 114.8 (111.8 C) 17

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

8.

P U G H AND PERCEC

Side-Chain Liquid Crystalline Polymers

99

when the anisotropy of the mesogen i s increased by increasing the number of s t i f f and highly polarizable units that i t contains. This in turn enlarges the mesogen, and i s most frequently achieved by attaching a polar substituent para to the polymerizable group of the monomer. A review of the literature demonstrates some trends concerning the e f f e c t of the polymer backbone on the thermotropic behavior of side-chain l i q u i d c r y s t a l l i n e polymers. In comparison to low molar mass l i q u i d c r y s t a l s , the thermal s t a b i l i t y of the mesophase increases upon polymerization (3,5,18). However, due to increasing v i s c o s i t y as the degree of polymerization increases, structural rearrangements are slowed down. Perhaps this i s why the isotropization temperature increases up to a c r i t i c a l value as the degree of polymerization increases (18). There are also some trends when looking at the main chain flexibility. Table II demonstrates that when the main chain flexibility decrease fro cyanobiphenyl containin polymethacrylates to polysiloxanes the isotropization temperatur opposite when the mesogen i s methoxyphenyl benzoate (18). Therefore, this e f f e c t of the main chain f l e x i b i l i t y i s s t i l l ambiguous. In order to determine the necessity and/or the length of the spacer that i s required to achieve l i q u i d c r y s t a l l i n e behavior from f l e x i b l e vs. r i g i d polymers, we have introduced mesogenic units to the backbones of a r i g i d [poly(2,6-dimethyl-l,4-phenylene oxide) (PPO)] and a f l e x i b l e [poly(epichlorohydrin) (PECH)] polymer through spacers of from 0 to 10 methylene groups v i a polymer analogous reactions. The synthetic procedure used for the chemical modification of PPO involved i n the f i r s t step the r a d i c a l bromination of PPO methyl groups to provide a polymer containing bromobenzyl groups. The bromobenzyl groups were then esterified under phase-transfer-catalyzed (PTC) reaction conditions with potassium 4-(4-oxybiphenyl)butyrate (Ph3C00K, Ph3C00-PP0), potassium 4- (4-methoxy-4'-oxybiphenyl)butyrate (Me3C00K, Me3C00-PP0), potassium 5-(4-oxybiphenyl)valerate (Ph4C00K, Ph4C00-PP0), potassium 5- (4-methoxy-4*-oxybiphenyl)valerate (Me4C00K, Me4C00-PP0), potassium ll-(4-oxybiphenyl)undecanoate (PhlOCOOK, PhlOCOO-PPO) and potassium ll-(4-methoxy-4'-oxybiphenyl) undecanoate (MelOCOOK, MelOCOO-PPO). The notations between parentheses correspond to the starting potassium s a l t and the resulting functionalized PPO. PECH was modified under similar reaction conditions, except that dimethylformamide (DMF) was used as the reaction solvent. In addition, the phase-transfer-catalyzed e t h e r i f i c a t i o n of the chloromethyl groups of PECH with sodium 4-methoxy -4 -biphenoxide was used to synthesize PECH with d i r e c t attachment of the mesogen to the polymer backbone. Similar notations to those used to describe the functionalized PPO are used for functionalized PECH. In this l a s t case, PPO was replaced with PECH. E s t e r i f i c a t i o n routes of both PPO and PECH are presented i n Scheme I. The attachment of mesogenic units to a polymer backbone v i a polymer analogous reactions i s not a new concept, although they are much less frequently used than the polymerization of mesogen containing monomers. Liquid crystalline polyacrylates, 1

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

100

CHEMICAL REACTIONS ON POLYMERS

Table I I . Influence o f the Main Chain F l e x i b i l i t y on L i q u i d C r y s t a l l i n e Phase T r a n s i t i o n s f o r Polymers w i t h Cyano-biphenyl as Mesogen

Main

chain

6

14

166

S

18

9

-1

157

Ν

19

2

50

112

Ν

20

5

40

120

Ν

20

6

35

125

S

18

11

25

145

S

20

2

95

5

60

121

S

20

6

55

100

S

18

11

40

121

S

20

Polysiloxane

Polyacrylate

20

Polymethacrylate

length o f methylenic u n i t s between mesogen and main chain

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

8.

P U G H AND PERCEC

Side-Chain Liquid Crystalline Polymers

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

101

102

CHEMICAL REACTIONS ON POLYMERS

polymethacrylates, and polyacrylamides have been prepared by conventional e s t e r i f i c a t i o n or amidation of poly(acryloyl chloridej and poly(methacryloyl chloride) with a mesogenic alcohol or amine i n the presence of triethylamine (8,21,22). Similarly, liquid c r y s t a l l i n e polyacrylates, polymethacrylates, and polyitaconates have been prepared by phase-transfer-catalyzed reactions on the sodium s a l t s of the corresponding polycarboxylates (23-25). In addition, alternating poly(methylvinylether-co-maleate) copolymers were prepared by the PTC reactions of poly(methylvinyletherco-disodium maleate) with mesogen containing bromoalkylesters (26). The most important use of this class of reactions, however, i s i n the preparation of l i q u i d c r y s t a l l i n e polysiloxanes, which cannot be obtained by any other method. We have recently summarized the work on the preparation of l i q u i d c r y s t a l l i n e polysiloxanes (19), which involves the platinum catalyzed hydrosilation reaction of v i n y l substituted mesogenic molecules with poly(hydrogen methylsiloxane) or i t s copolymers. Lastly, i t was series of a l k y l side-chain glas t r a n s i t i o n temperature decreases with an increase i n the side-chain length (28). At the same time, the Tg's of the more f l e x i b l e sidechain l i q u i d c r y s t a l l i n e polymers investigated to date are always much higher than those of the corresponding polymers without the mesogenic side-chains (_3). Therefore, i t i s quite l i k e l y that we may obtain side-chain l i q u i d c r y s t a l l i n e polymers of approximately the same Tg from PPO and PECH. Experimental The starting polymers were commercial products purified by p r e c i p i t a t i o n with methanol from chloroform solutions: PECH (B.F. Goodrich, Mn = 873,000, Mw = 10,250,000); PPO (Aldrich, Mn = 19,000m Mw = 49,000). The mesogenic units with methylenic spacers were prepared by reacting the sodium s a l t of either 4-methoxy-4'-hydroxybiphenyl or 4-phenylphenol with a bromoester i n DMF at 82 C for at least 4 hours i n the presence of tetrabutylammonium hydrogen sulfate (TBAH) as phase transfer catalyst. In this way, ethyl 4-(4-oxybiphenyl)butyrate, ethyl 4-(4-methoxy-4 -oxybiphenyl)butyrate, ethyl 4-(4-oxybiphenyl)valerate, ethyl 4-(4-methoxy-4'-oxybiphenyl)valerate, n-propyl 4-(4-oxybiphenyl)undecanoate and n-propyl 4-(4-methoxy-4'-oxybiphenyl)undecanoate were obtained. These esters were hydrolyzed with base and a c i d i f i e d to obtain the carboxylic acids. The corresponding potassium carboxylates were obtained by reaction with approximately stoichiometric amounts of potassium hydroxide. Experimental details of these syntheses were described elsewhere (27). Bromobenzyl groups were introduced into PPO by r a d i c a l bromination of the methyl groups. The PPO bromobenzyl groups and PECH chloromethyl groups were then esterified under phasetransfer-catalyzed reaction conditions with the potassium carboxylates just described. This procedure has been described previously (29). The sodium s a l t of 4-methoxy-4 -hydroxybiphenyl was also reacted with PECH (no spacer). Thermal analysis was performed with a Perkin-Elmer DSC-4 1

1

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

8.

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103

d i f f e r e n t i a l scanning calorimeter equipped with a Perkin-Elmer TADS thermal analysis data station. Heating and cooling rates were 20 C/min, and Indium was used as the c a l i b r a t i o n standard. A l l samples were heated to just above Tg and quenched before the f i r s t heating scan was recorded. A Carl-Zeiss o p t i c a l polarizing microscope equipped with a Mettler FP82 hot stage and FP80 central processor was used to analyze the anisotropic textures. Table III summarizes the reaction conditions and the results of the substitution of PPO for a l l reactions performed, while Table IV presents the results for the modification of PECH. Results and Discussion The synthetic route used for the chemical modification of PPO and PECH i s outlined i n Scheme 1. The results of the e s t e r i f i c a t i o n reactions of PPO and of PECH are summarized i n Tables III and IV respectively. I t was previously shown that the only available procedure for the nucleophili was by s o l i d - l i q u i d phase-transfe solvents (29), since PPO i s not soluble i n aprotic dipolar solvents which are required for conventional nucleophilic substitutions. In both cases, i t was necessary to use elevated temperature (60 C) to obtain good halide displacement. However, i t i s again demonstrated that PECH i s less reactive toward nucleophilic displacement than PPO. Although Me4C00K seem to result i n the most e f f i c i e n t substitution, and although the carboxylate n u c l e o p h i l i c i t i e s would be expected to change with d i f f e r e n t spacers, these results are not completely comparable due to d i f f e r e n t amounts of excess hydroxide present i n each displacement reaction. In addition, we found that sodium 4-phenylphenoxide degraded PECH to a number average molecular weight of approximately 3000, rather than s t r i c t l y displacing halide as was the case with the other nucleophiles. Table V summarizes the thermal characterization of substituted PPO, and demonstrates that although the Tg i s e a s i l y dropped with any of the substituents, l i q u i d c r y s t a l l i n e behavior i s not observed u n t i l 4-methoxy-4'-hydroxybiphenyl i s decoupled from backbone PPO by ten methylenic units. Therefore, l i q u i d c r y s t a l l i n e behavior can be obtained from very r i g i d polymers, provided a long enough spacer i s employed. A smectic l i q u i d c r y s t a l l i n e mesophase was confirmed by polarized o p t i c a l microscopy for MelOCOO-PPO, but the exact smectic phase could not be determined because some thermal crosslinking takes place during extensive annealing. This could be the result of the presence of unreacted bromobenzyl groups. In contrast to MelOCOO-PPO, PhlOCOO-PPO i s not l i q u i d c r y s t a l l i n e , although there i s comparatively l i t t l e substitution i n this case, p-biphenyl i t s e l f would not be expected to act as a mesogen i n such a rigid polymer due to i t s low degree of anisotropy and polarizability. Comparison ot Tables V and VI demonstrates that the thermal behavior of MelOCOO-PPO and MelOCOO-PECH are very similar, with the glass transition temperatures converging with substitution. Therefore, i t appears that when very long spacers are used with the same mesogen, the polymer backbone has l i t t l e e f f e c t on the thermotropic phases formed. This conclusion i s supported by additional unpublished experiments performed i n our laboratory.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS Table I I I .

Reaction Conditions and Results of Synthesis of PPO Containing Β1phenyl Groups *

Mole Fraction Moles per Mole -CH Br Structural Units Nucleophlle TBAH Conta1n1ng -CHgBr ?

Nucleophlle

1 2 3

biPhO-(CH ),C00K

Reaction Temp. Time (°C) (hr)

ZCH-Br SubStltuted

0.52 0.74 0.74

2.2 1.8 1.8

0.22 0.24 0.12

25 25 60

45 45 46

25 26 100

4 Me0-blPh0-(CH )-C00K 5 6

0.52 0.74 0.74

2.0 2.0 1.7

0.19 0.19 0.39

25 25 60

40 40 61.5

15 12 100

7 8 9

0.52 0.74 0.7

2.0 1.9

0.21 0.07

25 25

62 62

87 93

9

2

3

9

C

J

blPh0-(CH,) C00K A

6

4

10 Me0-blPh0-(CM C00K 11 12

0.5 0.74 0.74

2.1 2.0

0.10 0.39

25 60

62 61.5

13 14

0.52 0.74

2.0 1.9

0.12 0.21

25 25

96 96

15 Me0-blPh0-(CH,) C00K 0.74 16 0.74

0.9 0.9

0.24 0.24

60 60

A

£

4

blPh0-(CH,) C00K in

2

1 0

in

2

1 0

61 100 25 24 71 75

54.5 139.5

* Solvent • toluene

Table IV.

Reaction Conditions and Results of Synthesis o f PECH Containing Methoxyblphenyl Groups *

#

Nucleophlle

—

Moles per Mole -CHpCl Nucleophlle

TBAH

Reaction Time (hr)

ZCH C1 Substituted 2

1 2

Me0-blPh0Na

0.76 0.76

0.10 0.10

92 140

29 36

3 4 5 6

Me0-blPh0-(CH ) C00K

0.69 0.75 0.75 0.75

0.13 0.12 0.12 0.12

91 108.5 139.5 158.5

22 26 30 34

7 8 9 10 11 12 13 14

MeO-blPhO-iCHJ-COOK

0.75 0.75 0.75 0.73 0.75 0.75 0.75 0.75

0.12 0.12 0.12 0.11 0.12 0.12 0.12 0.12

19 49 83 91 115.5 140 159.5 181.5

23 42 52 51 62 65 65 65

15

MeO-blPHO-(CH ) CO0K

0.64

0.17

54

17

2

3

2

10

Solvent - DMF; 60°C

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

8.

P U G H AND PERCEC

Table V.

105

Side-Chain Liquid Crystalline Polymers

Thermal C h a r a c t e r i z a t i o n o f PPO C o n t a i n i n g B1phenyl Groups

Temperature (°C) a # Polymer Sample

Heatin g

1 2 3

0.13 Ph3C00-PP0 0.19 Ph3C00-PP0 0.74 Ph3C0O-PP0

4 5 6

0.08 Me3COO-PP0 0.09 Me3COO-PP0 0.74 Me3C00-PPO

172.5 155.2 69.4

7 8 9

0.43 Ph4C00-PP0 0.69 Ph4C00-PP0 0.74 Ph4C00-PP0

80.8 67.0 59.6

10 11 12

0.26 Me4C00-PP0 0.45 Me4C00-PP0 0.74 Me4C0O-PP0

106.2 89.2 62.5

13 14

0.13 PhlOCOO-PPO 0.18 Phl0C00-PP0

105.5 83.7

15 16

0.53 MelOCOO-PPO 0.56 MelOCOO-PPO

54.2 38.6

*\from T a b l e I I I ; ' b u r l e d 1n peak

b

g

141.7 130.0 69.5

58.4

85.6 53.1

72.4,

114.5 116.8, 129.0

39.2 c

77.5 40.4, 101.4

' mole f r a c t i o n o f mesogen s u b s t i t u t e d s t r u c t u r a l

units;

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

106

CHEMICAL REACTIONS ON POLYMERS

CM VO rH rH 00 00

rH 00 I HNCO H S H »ί · · · · I . . . . . . .HNO01 I CO rH VO toconooHO rOSOOCOHHHH

ο «± LD ^- oo r«. CSJ CM d -n cô

LocvjroovocNjr^rH

en

CO 00 00 VO

Cf> Ο «ςΓ rH

α rJ- ο 3 Ο •Ρ ο ί.Φ 40->0 0.rH Ε Φ

co Ν η σι en rH vo

ιο ο Ν e\j ι ι ι rH I

I

CM CM

ι

I

CO CM rH

VO CO 3 3 . .Ο Ο CM CM J= SZ U") CO 10 rH rH rH rH CD C O *C M * csj 00* un un un vo vo

00 d CO

CMCO d rH

rH en rH O * *t ο ο C I I

rH r-. VOο COCMΟ rH in νο «dd r*«' d ι rH rH co co COCO

3= ο Lu α. I ο φ Σ

3= Ο LU Ο­ Ι Ο Ο ο co φ Σ

3= Ο LU Ο­ Ι Ο Ο Ο

3= Ο Lu α. ι ο ΣΦ

en νο CMco ο ο

3= ο LU Ο­ Ι ο ο ο co φ Σ

vo" rH m

3= ο Lu CL I ο ο ο co φ Σ

χ ο Lu Ο­ Ι Ο Ο Ο CO φ Σ

CMνο ο «dCMCSJ COco Ο Ο Ο Ο

Un

d COCOun d

vo" rH vo d vo vo

3= 3= 3Ζ 3= 3= 3= Ο Ο Ο Ο Ο Ο Lu Lu Lu Lu Lu Lu Ο­ Ο­ Ο­ Ο­ Ο­ Ο­ Ι Ι Ι Ι Ι Ι Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο Ο

M

>

5

w

η Χ

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

14.

195

Photoozonization of Polypropylene

RABEK ET AL.

1.0-

QO-)

0

1

1

1

1

1

r

10

20

30

AO

50

60

Time ( min )

Figure 7. Kinetics of fluorescence disappearing at 340 nm of polypropylene films: ( O ) treated with ozone only; ( φ ) ozone and UV l i g h t (L2); ( Δ ) UV irradiated (L2) i n oxygen. Excitation wavelwngth 240 nm.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

196

There have been numerous t h e o r e t i c a l and e x p e r i m e n t a l e f f o r t s t o e x p l a i n t h e mechanism by which ozone r e a c t s w i t h double bonds o f u n s a t u r a t e d s u b s t a n c e s Q l , 1 2 , 3 5 ) . Perhaps t h e more w i d e l y a c c e p t e d r e a c t i o n i s t h e C r i e g e e mechanism which produces t h e two groups A and Β ( a s shown below) ( 36-42):

o-o-cr

0 /V R C=CR + 0 2

2

3

I - R C-CR

R2C—CR2

2

2

•R C-00

+ R C=0

2

2

(7)

P r o d u c t A, t h e s t r u c t u r e o f which C r i e g e e l e a v e s i n doubt, i s e x t r e m e l y u n s t a b l e and q u i c k l y r e v e r t s i n t o p r o d u c t s C and D through the i n t e r m e d i a t e B. The a n a l y s i s o f p u b l i s h e m o l e c u l a r hydrocarbons shows t h a t double bonds r e a c t w i t h ozone more q u i c k l y than s a t u r a t e d bonds ( 1 2 ) . Ozone r e a c t s w i t h s a t u r a t e d h y d r o ­ carbons i n r e a c t i o n s i n which hydrogen a b s t ^ a c t i o n 2 i s f o l l o w e d by r e - h y d r i d i z a t i o n o f t h e carbon atom form sp t o sp s t a t e (43,44):

C-H

HO*

+

products

0,

(8)

I t hag been shown t h a t t r a n s i t i o n o f a backbone carbon from t h e s p ^ t o sp s t a t e i s promoted by t e n s i l e s t r e s s e s and i n h i b i t e d by compressive s t r a i n s (10,44). The a c c e l e r a t i o n o f t h e p r o c e s s o f ozone o x i d a t i o n o f t h e polymers under l o a d i s n o t a s s o c i a t e d w i t h t h e changes i n s u p r a m o l e c u l a r s t r u c t u r e o r segmental m o b i l i t y o f t h e c h a i n . The p r o b a b l y r e a s o n o f t h i s e f f e c t i s a d e c r e a s i n g o f t h e a c t i v a t i o n energy f o r hydrogen a b s t r a c t i o n ( 4 4 ) . The mechanism o f i n i t i a l s t a g e s o f t h e r e a c t i o n o f ozone w i t h PP can be r e p r e s e n t e d as:

o +

-CH-CHI CH

ΌΗ

(rapid)

(9)

2

n

-CH-CH- + 0 2 1 3 CH 3

-CH -C9

+

o

2

+

CH -C- + 'OH ( r a p i d ) 1 0 z

CH. (POO")

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

(10)

14.

RABEKETAL.

197

Photoozonization of Polypropylene

The polymer peroxy r a d i c a l s (POO*) a r e d e t e c t e d by ESR s p e c t r o s c o p y ( F i g . l ) . T h i s i s p a r t i c u l a r l y i n t e r e s t i n g s i n c e n e i t h e r o f t h e proposed p r o d u c t s o f ozone c h a i n s c i s s i o n d e s c r i b e d p r e v i o u s l y i n t h e C r i e g e e mechanism a r e s u s c e o t i b l e t o d e t e c t i o n by ESR. I t can be, t h e r e f o r e , c o n c l u d e d t h a t subsequent o r a d d i t i o n a l r e a c t i o n s immediately occur a f t e r chain s c i s s i o n o r the decomposition of the z w i t t e r i o n t h r o u g h p r o t o n m i g r a t i o n t a k e p l a c e . The z w i t t e r i o n s ( r e a c t i o n 7) can be v e r y r e a c t i v e and r e a c t w i t h themselves o r o t h e r p a r t o f t h e c h a i n ( 4 2 ) . Another p o s s i b l e r e a c t i o n which c o u l d be c o n s i d e r e d i s t h a t t h e z w i t t e r i o n may s t r i p a hydrogen atom from another c h a i n . I f t h e f r e e r a d i c a l s a r e formed by a d i r e c t hydrogen a b s t r a c t i o n o r by secondary r e a c t i o n s o f these t y p e s , ESR does n o t p r o v i d e a d i r e c t measure o f bond r u p t u r e i n PP.Formation o f o x i d i z e d groups such as C=0, 00H o r COOH i s a r e s u l t o f secondary r e a c t i o n s i n which f o r m a t i o n o f polymer hydroperoxy r a d i c a l (POO*) seems t o be essential:

POO*

I

-CH-CH -

(slow)

(11)

(slow)

(12)

(slow)

(13)

2

A l l o f t h e c h e m i c a l changes t h a t r e s u l t from o z o n i z a t i o n a r e o x i d a t i v e r e a c t i o n s i n c l u d i n g t h e b r e a k i n g o f t h e polymer c h a i n . A PP sample a f t e r o z o n i z a t i o n i n t h e presence o f U V - i r r a d i a t i o n becomes b r i t t l e a f t e r 8 h r s o f e x p o s u r e , whereas t h e same e f f e c t i n ozone i s n o t i c e a b l e a f t e r 50-60 h o u r s . D e g r a d a t i o n o f polymer c h a i n o c c u r s as a r e s u l t o f d e c o m p o s i t i o n o f peroxy r a d i c a l s . The o x i d a t i o n r a p i d l y reaches s a t u r a t i o n , suggesting the surface nature o f ozone and atomic oxygen a g a i n s t o f PP as a consequence o f l i m i t e d d i f f u s i o n o f both oxygen s p e c i e s i n t o t h e polymer. Ozone r e a c t s w i t h PP m a i n l y on t h e s u r f a c e s i n c e t h e r e a c t i o n r a t e and t h e c o n c e n t r a t i o n o f i n t e r m e d i a t e peroxy r a d i c a l s a r e p r o p o r t i o n a l t o t h e s u r f a c e a r e a and n o t the weight o f t h e polymer. I t has been found t h a t p o l y e t h y l e n e i s a t t a c k e d o n l y t o a depth o f 5-7 m i c r o n s ( 4 5 ) . Atomic oxygen o x i d a t i o n o f polymers has been r e p o r t e d by a few a u t h o r s ( 4 6 , 5 0 ) . Experiments were l i m i t e d t o the measurements o f w e i g h t - l o s s d a t a and changing o f the w e t t e a b i l i t y ( 4 6 - 4 8 ) , and o n l y two papers were devoted t o t h e study mechanism o f atomic oxygen o x i d a t i o n of polydienes (49,50). The PP samples exposed t o atomic oxygen show f o r t h e f o r m a t i o n o f polymer peroxy r a d i c a l s (POO*), which g i v e almost i d e n t i c a l ESR spectrum as i n t h e case o f ozone r e a c t i o n ( F i g . l ) . The ESCA s p e c t r a ( F i g . 5 ) i n d i c a t e t h a t atomic oxygen o x i d a t i o n i s more e f f e c t i v e than o z o n i z a t i o n . These r e s u l t s s u p p o r t our assumption t h a t o z o n i z a t i o n

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

198

CHEMICAL REACTIONS O N POLYMERS

of PP f i l m i n the presence o f U V - i r r a d i a t i o n i s probably a r e s u l t o f s i m u l t a n e o u s a t t a c k o f atomic oxygen, m o l e c u l a r oxygen (which i s p r e ­ sent i n e x c e s s i n ozone-oxygen m i x t u r e ) and ozone (which was n o t c o m p l e t e l y p h o t o l y s e d ) . Oxygen atoms were g e n e r a t e d by p h o t o l y s i s o f ozone, u s i n g t h e 253,7 nm l i n e from L I lamp. The i n i t i a l l y formed e x c i t e d oxygen atoms 0( D) a r e r a p i d l y d e a c t i v a t e d t o t h e ground s t a t e atomic oxygen 0, by c o l l i s i o n s w i t h t h e e x c e s s o f ozone mole­ c u l e s p r e s e n t . I n t h i s method i t i s i m p o s s i b l e t o s e p a r a t e both s p e c i e s , a t o m i c oxygen and ozone. mer

Mechanism o f t h e r e a c t i o n s which a r e b e l i v e d t o o c c u r when a p o l y ­ such as PP i s exposed t o atomic oxygen a r e f o l l o w i n g : H I -CH -Cζ ι CH^

+

-CH -C-

+

2

CH

— • -CH -C- + Zj CH^

*0H — - C H

2

2

CH

+

"OH — •

"OH

- Ç -

3

-CH -CCH

0

CH

(14)

(rapid)

(15)

(rapid)

(16)

(rapid)

(17)

3

-CH=C-

3

(rapid)

+ H 0 2

3

00"

I -CH -Ç-

+

2

CH

0

^

2

-CH -C2

CH

3

3

(POO*)- d e t e c t e d

-CH=C-

+

0

3

— •

products according reaction 7

POO"

+ PH

— • POOH

POOH

— •

P0"

+

+

"OH

P"

by ESR

spectroscopy

(rapid)

(18)

(slow)

(19)

(slow)

(20)

Slow r e a c t i o n which also occur during photo-oxidation and/or thermal o x i d a t i o n can take p l a c e d u r i n g o x i d a t i o n w i t h atomic oxygen, but t h e s e slow r e a c t i o n s a r e o f l i t t l e importance because o f t h e r a p i d o x i d a t i o n which u s u a l l y o c c u r s . More r e s u l t s which e x p l a i n atomic oxygen o x i d a t i o n mechanism o f PP, w i l l be p u b l i s h e d s e p a r a t e l y . Acknowledgnent. These investigations are part of a research program on the environmental degradation of polymers supported by the Swedish National Board for Technical Developments (SIU), which we gratefully acknowledge.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

14.

RABEK ET AL.

Photoozonization of Polypropylene

199

Literature Cited 1. Finlayson-Pitts,B.J. and Pitts, J.N.Jr., "Atmospheric Chemistry: Fundamentals and Experimental Techniques",Wiley,New York,1986. 2. Boutevin, B., Pietrasanta, Y., Taha, Μ., and Sarraf, T., Europ.Polym.J.,20,875 (1984). 3. Giesler, G.,and Wergin, H., J.für Prakt.Chem.,25,135-140 (1964). 4. Giesler, G., and Wergin, H., J. für Prakt.Chem.,25,141 (1964). 5. Kefeli, Α.Α., Razumovskii, S.D., and Zaikov, G.E., Polym.Sci. USSR, 13,904 (1971). 6. Kefeli, Α.Α., Razumovskii, S.D., Markin, V.S., and Zaikov, G.E., Vysokomol.Soedin., A,14,2413 (1972). 7. Lazar, Μ., Rubb.Chem.Technol., 36,527 (1963). 8. Lebel, P.H., Rubb.Plast.Age, 45,297 (1964). 9. Peeling, J . , and Clark, C.T., J.Polym.Sci., A1,21,2047 (1983). 10. Popov, Α.Α., Krisyuk, B.E., Blinov, N.N., and Zaikov, G.E., Europ.Polym.J., 17,169 (1981). 11. Razumovskii, S.D. (1985). 12. Razumovskii, S.D., and Zaikov, G.E., "Ozone and Its Reactions with Organic Compounds",Elsevier, 1984. 13. Priest, D.J., J.Polym.Sci., A2,9,1771 (1971). 14. Kefeli, Α.Α., Rakovskii, S.K., Shopov, D.M., Razumovskii, S.D., Rakovskii, R.S., and Zaikov, G.E., J.Polym.Sci.,A1,19,2175 (1981). 15. Razumovskii, S.D., Karpukhin, O.N., Kefeli, Α.Α., Pokholok,T.V., and Zaikov, G.E., Vysokomol.Soedin.,A,13,782 (1971). 16. Abdullin, M.I., Gataullin, R.F., Minsker, K.S., Kefeli, Α.Α., Razumovskii, S.D., and Zaikov, G.E., Europ.Polym.J.,14,811 (1978). 17. Devries, K.L., and Simonson, E.R., Ozone Chem.Technol.,1975,257. 18. Razumovskii, S.D., Kefeli, Α.Α., and Zaikov, G.E., Europ.Polym. J.,7,275 (1971). 19. Tucker, H., Rubb.Chem.Technol.,32,269 (1959). 20. Yakubchik, A.I., Kasatkina, N.G., and Pavlovskaya, T.E., Rubb. Chem.Technol.,32,284 (1959). 21. Calvert, J.C., and Pitts, J.N.Jr., "Photochemistry", Wiley,New York,1967,p.209. 22. Okabe, H., "Photochemistry of Small Molecules", Wiley,New York, 1978,p.237. 23. Rånby, Β., and Rabek, J.F., "Photodegradation, Photooxidation and Photostabilization of Polymers", Wiley, London, 1975,p.254 and 351. 24. Rånby, Β., and Rabek, J.F., in "The Effects of Hostile Environ­ ments on Coatings and Plastics", (Garner, D.P., and Stahl, G.A., eds), ACS Symp.Ser.,No229,Washington, DC, 1983,p.291. 25. Carlsson, D.J., Suprunchuk, T., and Wiles, D.M., J.Polym.Sci., B,14,193 (1976). 26. Carlsson, D.J., and Wiles, D.M., J.Polym.Sci.,A1,14,493 (1976). 27. Rabek, J.F., in "Singlet Oxygen" (Frimer, A.A.,ed.),Vol.4,CRC Press,Boca Raton,FL,1985,p.1. 28. Dilks, Α., J.Polym.Sci.,A1,19,1319 (1981). 29. Rånby, Β., and Rabek, J.F., "ESR Spectroscopy in Polymer Research", Springer Verlag,Berlin,1977,p.257.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

200

CHEMICAL REACTIONS O N POLYMERS

30. Yamauchi, J., Ikemoto, K., and Yamaoka, Α., Makromol.Chem.,178, 2483 (1977). 31. Carlsson, D.J., and Wiles, D.M., Macromolecules,4,174 (1971). 32. Kefeli, Α.Α., Razumovskii, S.D., Markin, V.S., and Zaikov, G.E., Polym.Sci.,USSR,14,2812 (1972). 33. Amin, M.U., Tillekeratne, L.M.K., and Scott, G., Europ.Polym.J., 11,85 (1976). 34. McKellar, J.F., and Allen, N.S., "Photochemistry of Man-Made Polymers",Applied Science Publishers,London, 1979,p.10. 35. Bailey, P.S., "Ozonization in Organic Chemistry", Vol.1-2, Academic Press, New York, 1982. 36. Criegee, R., Record of Chemical Progress,18,111 (1957). 37. Criegee, R., Kerckov, Α., and Zinke, H., Chem.Berichte,88,1878 (1955). 38. Criegee, R., and Wenner, G., Justus Liebigs Ann.Chem.,564,9 (1959). 39. Murray, R.W., Acc.Chem.Res.,1,313 (1968) 40. Gillies, C.W., and 41. Kuczkowski, R.L., Acc.Chem.Res.,16,4 (1983) 42. Bailey, P.S., Chem.Rev.,58,925 (1958). 43. Popov, Α.Α., Rakovskii, S.K., Shopov, D.M., and Ruban, Z.V., Izv. Akad.Nauk SSSR, 982,1950 (1976). 44. Popov, Α.Α., and Zaikov, G.E., Dokl.Akad.Nauk SSSR, 244,1178 (1979). 45. Pentin, Yu.A., Tarasevich, B.N., and El'tsefon, Β., Zhurn.Fiz. Khim.,46,2116 (1972). 46. Hansen, R.H., Pascale, J.V., De Benedictis, T., Rentzepis, P.M., J.Polym.Sci.,A,3,2205 (1965). 47. MacCallum, J.R., Rankin, C.T.,J.Polym.Sci.,9,751(1971). 48. MacCallum, J.R., Rankin, C.T., Makromol.Chem.,175,2477 (1974). 49. Rabek, J.F., Lucki, J., and Rånby, Β., Europ.Polym.J.,15,1089 (1979). 50. Lucki, J., Rabek, J.F., and Rånby, Β., Europ.Polym.J.,15,1101 (1979). RECEIVED September

11,1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter

15

Photochemical Modifications of Poly(vinyl chloride) Conducting Polymers and Photostabilization C. Decker Laboratoire de Photochimie Générale associé au Centre National de la Recherche Scientifique, Ecole Nationale Supérieure de Chimie, 68200 Mulhouse, France

Polyvinyl chlorid tions in order to either produce a conductive polymer or to impro ve its light-stability. In the first case, the PVC plate was ex­ tensively photochlorinated and then degraded by UV exposure in N . Total dehydrochlorination was achieved by a short Ar laser irra­ diation at 488 nm that leads to a purely carbon polymer which was shown to exhibit an electrical conductivity. In the second case, an epoxy-acrylate resin was coated onto a transparent PVC sheet and crosslinked by UV irradiation in the presence of both a photo­ initiator and a UV absorber. This superficial treatment was found to greatly improve the photostability of PVC as well as its surfa­ ce properties. 2

+

UV r a d i a t i o n i s known to have deleterious e f f e c t on most commercial polymers, thus reducing the service l i f e of these mater i a l s for outdoor applications. That i s p a r t i c u l a r l y true f o r PVC, one o f the most widely used thermoplastics, whose f i e l d of applications s t i l l remains r e s t r i c t e d by i t s poor resistance to sunlight 0 ) . In some cases, i t i s also possible to p r o f i t from the energy c a r r i e d by the photons to induce useful chemical modifications that w i l l generate new materials with improved properties. These photochemical reactions w i l l develop p r i m a r i l y at the surface and i n the top layer o f the i r r a d i a t e d polymer because of the limited penetrat i o n o f UV radiation into organic compounds. We describe here two examples o f such light-induced surface modifications that were both c a r r i e d out on a PVC substrate. In the f i r s t one, the polymer was exposed successively to UV r a d i a t i o n and to a l a s e r beam i n order to produce a purely carbon polymer that was shown to be able to carry electrons. The second example shows how the l i g h t s t a b i l i t y of PVC can be greatly improved by protecting the surface of PVC-based materials with a UV curable coating that acts as an e f f e c t i v e anti-UV f i l t e r . 0097-6156/88/0364-0201 $06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

202

CHEMICAL REACTIONS ON

CONDUCTING POLYMERS BY LASER CARBONIZATION OF

POLYMERS

PVC

Synthetic polymers are best known f o r t h e i r insulating d i e l e c t r i c properties which have been exploited f o r numerous applications i n both the e l e c t r i c a l and e l e c t r o n i c industries. I t was found recently that some polymers can also be rendered conduct i v e by an appropriate treatment, thus opening the way to a new f i e l d of applications of these materials (2, _3). Usually, e l e c t r i c a l conductivity i s obtained by doping a neutral polymer, r i c h i n unsaturation, with donor or acceptor molecules. These polymers are rather d i f f i c u l t to synthesize, which makes them very expensive ; besides they are often sensitive to environmental agents, l i k e oxygen or humidity, thus r e s t r i c t i n g t h e i r p r a c t i c a l use to oxygen-free systems. In the present work, a somewhat d i f f e r e n t approach was chosen i n order to produce conducting polymers ; the basic idea was to s t a r t with a cheap material hydrogen and chlorine atom material thus obtained wa expecte d u c t i v i t y of a semimetal, while being insensitive to the atmospheric oxygen. In this paper, we report f o r the f i r s t time how PVC can be completely dehydrochlorinated by simple exposure to a powerful laser beam that combines both the photochemical and the thermal e f f e c t s . In a previous work (4, 5_), we have shown that long conjugated polyene sequences, -(CH=CH-CH=CH)-, are formed i n large amounts during the laser-induced degradation of PVC, leading to a heavily colored polymer f i l m . However, to make this material conductive, doping with an appropriate agent l i k e iodine or boron t r i f l u o r i d e (6) i s s t i l l necessary, since t o t a l dehydrogenation into graphite cannot be worked out under those conditions. The s i t u a t i o n i s quite d i f f e r e n t i f chlorinated PVC (C-PVC) i s used as s t a r t i n g material. This polymer was found to be very sensitive to UV radiation ( 7 ) , generating chlorinated polyene sequences, -(CH=CC1-CH=CC1)^, with high quantum y i e l d s ; such structures are susceptible to be further dehydrochlorinated into a purely carbon polymer by photochemical or thermal degradation. I f a laser i s used to perform this reaction, one can expect to thus achieve an extremely fast and extensive carbonization of the polymer and produce conductive patterns i n well defined areas. The whole procedure can be represented by the following reaction scheme :

hv •(CH -CH) 2

-(CH=CH-CH=CH) - + HC1

n

n

1

laser

CI CI9

hv

hv " (ÇH-CH) CI CI

n

chlorinated PVC

laser -(CH=Ç-CH=Ç) CI CI

n

chlorinated polyenes

-(

C=C

V

carbon

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

+

HC1

15.

DECKER

Photochemical Modifications of PVC

203

B a s i c a l l y , i t consists of three photochemical processes that are i l l u s t r a t e d by figure 1 : - the light-induced chlorination of PVC, - the photodegradation of the r e s u l t i n g chlorinated PVC, - the laser-induced dehydrochlorination of the degraded C-PVC. Each of these processes w i l l now be described i n d e t a i l . 1. Photochlorination_of_PVC When a PVC f i l m i s exposed to the UV-visible radiation of an incandescent lamp i n the presence of pure chlorine, at room temperature, the chlorine content of the polymer increases from 56.8 % i n i t i a l l y to over 70 % a f t e r a few hours of i r r a d i a t i o n (8). As the reaction proceeds, the rate o f chlorination decreases s t e a d i l y as shown by the k i n e t i c curves of figure 2, most probably because of the decreasing number of reactiv s i t e th polyme chai that remain available f o r th At the same time, large amounts of hydrogen chloride are evolved, at a rate very s i m i l a r to the rate of chlorine addition to PVC (figure 2). This i s i n good agreement with the postulated react i o n scheme, shown i n figure 3, that predicts the formation of one HC1 molecule f o r each chlorine atom fixed to the PVC backbone. Quantum y i e l d measurements have shown that t h i s chain reaction process develops very e f f i c i e n t l y i n t h i n PVC films, each chlorine r a d i c a l generated by photolysis of C l being able to induce the chlorination of up to 30 methylene s i t e s (9). 2

In order to evaluate how deep the chlorination can proceed into the polymer f i l m , photochlorination experiments were c a r r i e d out on PVC samples of various thickness i n the 5 to 60 urn range. Figure 4 shows that extensive chlorination only occurs i n the top layer, but that chlorine r a d i c a l s can s t i l l penetrate as much as 30 ym deep into the PVC f i l m , thus leading to a gradient of c h l o r i nation that leaves e s s e n t i a l l y unchanged the deep underlying layers. For some s p e c i f i c applications, a thicker layer of conductive polymer, and therefore of C-PVC, might be needed. This can be obtained by using as s t a r t i n g material a PVC powder that has been extensively chlorinated i n a f l u i d bed reactor or i n a v i b r a t i n g photoreactor (10), at conversions above 90 % . C-PVC films of required thicknesses can then be cast on the PVC substrate. The l a t t e r method has also to be used when the conducting patterns must appear on a support other than PVC, such as metals, glass or other p l a s t i c s . 2 · Ph2£2d2gI§dation_of2IΣ§£Ë 3 0 0 nm

hv

hv

CL

La s e r

λ > 250nm

III

Ν.

II I

488 nm

Air

PVC CHLORINATION

CHLORINATION

-{CHCI-CHCI} π

4 C H = CCl4η

ί

C: C i

Figure 1. Three step procedure of the carbonization of PVC by UV and laser i r r a d i a t i o n

Irradia

tion

time

(hours)

Figure 2. Kinetics of the photochlorination of a PVC f i l m (thickness = 50 ym ; l i g h t i n t e n s i t y = 5.10" Ε s"' cm" ) 9

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2

15.

DECKER

Photochemical Modifications of PVC

P V C

CL

hv

205

HCI

~CH-CH< I Cl

-Cl

- C H - C H -

Figure 3. Reaction scheme of the photochlorination of PVC by a chain process

Chlorine

content(Vo)

Conversion(Yo)

C-PVC

100

10

20

Film

thickness

30

40

50

60

(microns)

Figure 4. Dependence of the chlorine content of C-PVC on the f i l m thickness, after 7h of UV exposure. Calculated curves i f the chlorination were r e s t r i c t e d to the 20 ym ( — ) or 30 ym (...) top layer

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

The intense d i s c o l o r a t i o n which developed r a p i d l y upon UV exposure reveals the high photosensitivity of C-PVC that i s even more pronounced than f o r PVC i t s e l f , as shown by the UV-visible absorption spectra of figure 5. A f t e r 15 minutes of i r r a d i a t i o n , l a r ge amounts of polyenes have already accumulated i n C-PVC, with sequence lengths up to 20 conjugated double bonds, while PVC i s hardly affected after that short exposure. The mechanism of the photodegradation of C-PVC has been extensively studied Ç7 >H) > ^ summarized by the following reaction scheme : c

hv

^H-Cttx, • ι CI CI

a

- %CH-CH\, + I

CI

n

e

CI C-PVC •

+

HCl

^H=CH

chlorinated PVC

HCl

^C -CH^

^C=CH-CH^ ι ι CI CI

M^CH-C^CI

I

CI

+

'zip" CI

'vC=CH-C=CHb I

CI

-^(CH^-CH^)^

I

CI

CI

CI

chlorinated polyenes

Once UV photons have been absorbed by the polymer, excited states are formed ; they disappear by various routes, one of them leading to the formation of free r a d i c a l s by cleavage of the C-Cl bonds. The very reactive CI r a d i c a l s evolved are most l i k e l y to abstract an hydrogen atom from the surrounding CHC1 s i t e s to generate α-β,β' chloro a l k y l r a d i c a l s : -CH-C-CH-. These radicals are known to s t a 7

I I I

CI C1C1 b i l i z e r e a d i l y by s p l i t t i n g o f f the 3 chlorine with formation of a double bond (12). I f the *C1 r a d i c a l evolved reacts with the close by a l l y l i c hydrogen, a new unstable r a d i c a l w i l l be formed so that the dehydrochlorination w i l l develop step by step along the polymer chain, leading to the formation of chlorinated polyene sequences and evolution of hydrogen chloride. It should be mentioned that, besides t h i s e f f i c i e n t chain reaction process, main chain scissions and crosslinking were also found to occur to some extent during the light-induced degradation of C-PVC films (11) ; these reactions are yet not l i k e l y to a f f e c t the production of a purely carbon polymer i n the t h i r d and l a s t step of the procedure.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

15.

DECKER

Photochemical Modifications of PVC

207

3. Laser_carbonization_o£_deg Since our main objective was to remove a l l the chlorine and hydrogen atoms from the polymer chain, C-PVC films were further exposed to the UV radiation of the medium pressure mercury-lamp. This led to a dark brown material w.hich was found to be unable to carry an e l e c t r i c a l current, even a f t e r extended i r r a d i a t i o n time. Therefore we turned to a powerful laser source, a 15 W argon ion laser tuned to i t s continuous emission at 488.1 nm. At that wavelength, the degraded polymer f i l m absorbs about 30 % of the incident laser photons. The sample was placed on a X-Y stage and exposed to the laser beam at scanning rates i n the range of 1 to 50 cm s , i n the presence of a i r . A laser power output of 1 W, concentrated on a t i n y area of 2 mm, proved to be already enough to transform the polymer into a black residue at a scanning speed of 2 cm s~1, which corresponds to an exposure time as shor e s s e n t i a l l y of carbon ; vents and was found to t o t a l l y wavelength spectrum, from the deep UV to the v i s i b l e and infra-red regions (13). Upon laser exposure, large amounts of hydrogen c h l o r i de- were evolved, thus r e s u l t i n g i n a substantial weight loss of the laser i r r a d i a t e d sample ; gravimetric measurements have shown that e s s e n t i a l l y a l l the chlorine atoms have been removed from the polymer backbone, the apparent density of the l a s e r - i r r a d i a t e d material dropping to about 0.5g cm~3. This r e s u l t was confirmed by infra-red spectroscopy analysis which c l e a r l y revealed that a l l the functional groups have disappeared, i n p a r t i c u l a r the C-Cl bonds that absorb i n the 700 cnr1 region (figure 6). A l l the spectroscopy measurements were c a r r i e d out on a sodium chloride or quartz plate coated with a 20 urn thick C-PVC f i l m . 2

If f a s t e r scanning rates are required f o r some s p e c i f i c app l i c a t i o n s they can e a s i l y be reached either by increasing the power output of the laser up to 5 W, or by focusing the beam down into the micron range. Table I compares the results obtained with the unfocused laser beam and with a 100 or 10 ym laser spot. With the most sharply focused beam, carbonization a l r e a l y occured at a scanning speed of 50 cm s~1 and the exposure time dropped into the microsecond range. One of the main c h a r a c t e r i s t i c s of the laser emission i s the huge amount of energy that i s concentrated within a narrow beam and can be delivered on a t i n y area. In order to take f u l l p r o f i t of the high power density available, i t i s also necessary to use photosensitive systems which obey the r e c i p r o c i t y law, i . e . where the energy required f o r the reaction i s not dependent on the l i g h t intensity, which means that the quantum y i e l d remains constant. This condition appears to be almost f u l l f i l l e d i n the present case since the fluence, expressed i n J cm" , was found to increase by only a factor of 4 when the l i g h t - i n t e n s i t y was increased by over 4 orders of magnitude (Table I ) . 2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

208

CHEMICAL REACTIONS ON POLYMERS Polyene 4

2

Absorban i c e

1.0

sequence / 8 10

6

englh 15

ι

\

0.5

C-PVC \

V

PVC

\

t=15

t=15'

\

\ t«o

\

0

300

400

Wove

I eng /h

500

600

(nm)

F i g u r e 5. U V - v i s i b l e a b s o r p t i o n s p e c t r a o f PVC and C-PVC f i l m s b e f o r e and a f t e r 15 m i n o f UV i r r a d i a t i o n i n a N atmosphere 2

Chlorina

Laser

l

tea

irradia

t ed

ι

2000 '

1500

Wave

number

PVC

C-PVC

ι

1000

I

600

1

(cm- )

F i g u r e 6. IR a b s o r p t i o n s p e c t r a o f c h l o r i n a t e d PVC b e f o r e and a f t e r l a s e r i r r a d i a t i o n a t 488 nm f o r 0.1 s i n a i r

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

15.

DECKER

209

Photochemical Modifications of PVC

Table I : Influence of the beam focusing i n the lasergraphitization of chlorinated PVC (continuous wave mode emission line at 488.1 nm o f A r

λ = 488.1 nm

+

laser)

Argon-ion laser beam focused

unfocused

Power = 1 W

0.,1

1.7

Spot diameter (nm) 2

Fluence rate (Wcnf ) Scanning speed (cm s"^)

0.01

L

6

50

10

2

10

50

5

10

20

12

6

3

4

1 0

Exposure time (s) Fluence (Jem

)

Quantum y i e l d

The quantum y i e l d of the carbonization process can be eva­ luated from the amount of HCl evolved during the laser i r r a d i a t i o n _

A

number of molecules of HCl evolved

__ ψ 2

number of photons absorbed

carbon

taking into account that 2 molecules of HCl are evolved from C-PVC for each =C=C= unit formed. Since only 30 % of the incident laser photons are absorbed by the polymer f i l m , the amount o f energy absorbed i n a 1cm area illuminated f o r 0.1 s by the unfocused laser beam w i l l be : 5 J cm"" χ 0.3 = 1.5 J cm" or 6 χ 10~ e i n s t e i n cm" (1 e i n s t e i n associated with the 488 nm emission has an energy of 2.45 x10 Joule mole"'). On the other hand, about 7 χ 10" mole of HCl are evolved by each square centimeter of a 20 ym C-PVC f i l m transformed into carbon. The quantum y i e l d of HCl evolved can then be calculated from the following r a t i o : 2

2

2

6

2

5

5

φ = HC1

7

^carbon

=

Η Γ 1

T

χ 10-5 mole cm-2 , _6 . . -7 6 χ 10 e i n s t e i n cm 1Π

^

m o

^

ϋ

e

=

einstein"

1

L

einstein" 1

These quantum y i e l d values appear to be much higher than unity and therefore demonstrate that carbonization occurs by a chain reaction process. The mechanism of the laser-induced dehydrochlorination of photodegraded C-PVC can be schematically represented by the f o l i o -

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

210

wing set of reactions, that leads ultimately to a purely carbon polymer made of either l i n e a r sequences or polycondensed double bonds : laser

-(CH=C-CH=C)-

CI + -C=CH-C=CHI

»

CI

HCl + -C=C=C=C-Cι

CI

I

CI

CI

n

488

-C=C-C=CHI

-CH=£-CH=CI

nm

I

+

CI

CI +

HCl

+

CI

CI , CI

CI

•

I

I

CI

-C=C=C=CHI

CI

CI + -c=c=c=c=cI

CI This reaction scheme bears some formal analogy with the mechanism previously elaborated f o r the laser-induced degradation of PVC (3,4), except that the 488 nm laser photons are now absorbed by the chlorinated polyenes, with a sequence length of about 12. One of the important routes of deactivation of the excited states thus formed i s by cleavage of the most l a b i l e a l l y l i c C-Cl bond, with l i b e r a t i o n of a very reactive *C1 r a d i c a l that w i l l r e a d i l y abstract an hydrogen atom from the surrounding polymer chains. The r e s u l t i n g 3,3' c h l o r o a l l y l i c r a d i c a l tends to s t a b i l i z e by s p l i t t i n g o f f a chlorine atom, thus generating a =C=C= type structure. As t h i s chain reaction propagates along the polymer backbone, a purely carbon material i s f i n a l l y formed, together with large amounts of HCl. Since the UV degraded C-PVC s t i l l contains substantial amounts of the i n i t i a l CHC1-CHC1 structure, one can expect the chlorine r a d i c a l s evolved to also i n i t i a t e the zip-dehydrochlorinat i o n of these structures. The r e s u l t i n g chlorinated polyenes w i l l then be further destroyed by the laser i r r a d i a t i o n , so that f i n a l l y a l l the C-PVC polymer i s converted into a purely carbon material within a f r a c t i o n of a second. 4. E l e c t r i c a l _ c o n d u c t i v i t Y The black l i n e s that appear on the C-PVC plate a f t e r scan­ ning by the laser beam were found to 'consist e s s e n t i a l l y of carbon and were thus expected to exhibit some e l e c t r i c a l conductivity. Indeed, when a low voltage was applied to both çnds of the laser tracks, the t i n y filament turned bright red and even incandescent when a p o t e n t i a l over 30 V was applied. This c l e a r l y shows that the laser i r r a d i a t i o n can transform an insulating polymer l i k e C-PVC into a conductive material. Thus, i t becomes possible to write high resolution conductive patterns with t h i s l i g h t - p e n c i l which can be e a s i l y v i s u a l i s e d since they appear as well contrasted black tracks. By measuring the resistance (R) of these laser tracks, one can evaluate the e l e c t r i c a l conductivity (σ) of the polymer formed from the equation :

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

15.

Photochemical Modifications of PVC

DECKER

211

where I i s the length of the wire of cross-section S. The conducti­ v i t y was found to be ^ 10Ω"^αη"1, a value comparable to the conduc­ t i v i t y of p r i s t i n e graphite (σ =8.3 Ω~1 cnf^) when i t i s measured in the d i r e c t i o n perpendicular to the planes containing the carbon atoms (14). Since the conductivity of the starting polymer i s i n the range of 10" 10 Cr^cm~\ we are thus achieving through the laser i r r a d i a t i o n a remarkable and instantaneous jump of 11 decades i n the e l e c t r i c a l conductivity of this material. c

A higher conductivity might s t i l l be obtained i f necessary, either by compacting the porous carbon structure or by inserting acceptor or donor molecules. Thus, i n the case of p r i s t i n e graphite, the perpendicular to the plane conductivity was found to increase to 2.10^ Ω~' cm"' by insertion of potassium intercalates and as high as 8.10 Ω" cm" by using lithium (J4-) 4

1

1

The o v e r a l l procedur into carbon i s summarized by the diagram of figure 7 that c l e a r l y shows the three successive photochemical processes. I t should be mentioned that the laser i r r a d i a t i o n of PVC or photodegraded PVC produces no conductive polymer but leads, after prolonged exposure, to a brown material resulting from both thermal and photochemical degradations. One of the main advantages of using chlorinated PVC i s that this polymer combines both a high photosensitivity, thus requiring short exposure times, and a good thermal s t a b i l i t y (Tg > 150°C) which precludes any phase changes during the laser exposure. For p r a c t i c a l applications of these conducting polymers i n the electronic industry, i t i s s t i l l necessary to use a top coat to protect the t i n y carbon patterns which are rather f r a g i l e due to t h e i r porous structure. A photopolymerizable a c r y l i c r e s i n was f o r ­ mulated f o r that purpose that had a r e l a t i v e l y large v i s c o s i t y and a high r e a c t i v i t y , both factors which prevent any s i g n i f i c a n t d i f ­ fusion of the r e s i n into the carbon structure during the short time lapse between deposit and f i n a l cure. A very resistant coating was thus obtained a f t e r UV exposure during a f r a c t i o n of a second ; i t was found to s t i l l preserve the e l e c t r i c a l conductivity of the laser tracks and allows an easy handling of the plates, without r i s k i n g to erase the conductive c i r c u i t s . Besides, such a treatment also ensures a good adhesion of the patterns to the support, i n p a r t i c u ­ lar i f the l a t t e r consists of a material other than PVC, where adhesion was found to be poor before treatment by the UV curable coating. 5. Conclusion In the present study i t has been shown f o r the f i r s t time that chlorinated PVC can be r e a d i l y transformed into a conducting polymer by simple laser i r r a d i a t i o n i n the presence of a i r . The resulting material consisted e s s e n t i a l l y of carbon and proved to be able to carry electrons, without any doping procedure. By focusing the laser beam down into the micron range, i t becomes thus possible

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

212

CHEMICAL REACTIONS ON POLYMERS

to d i r e c t l y write highly complex conductive patterns on a chlorinated PVC f i l m coated onto a transparent substrate, at scanning speeds up to 50 cm s"^. For an easy handling of such plates, the f r a g i l e image has to be protected by a UV-cured coating that i s both r e s i s tant to abrasion and scratching and inert toward environmental agents l i k e humidity, a c i d i c pollutants or organic solvents. Potent i a l applications of such organic metals are expected to be found mostly i n the microelectronic industry f o r the production of highresolution conducting devices. PHQTOSTABILIZATION OF PVC BY UV CURED COATINGS Among the most widely used thermoplastic polymers, PVC i s known to exhibit the highest s e n s i t i v i t y toward sunlight. Solar radiations were shown (1) to induce a fast dehydrochlorination react i o n leading to the production of highly colored polyene structures as well as to the formation of crosslinks and chain s c i s s i o n s , with a subsequent loss i n th mechanical performances Th t l to improve the d u r a b i l i t b i l i z e r s or pigments l i k In the case of transparent PVC, the outdoor service l i f e s t i l l does not exceed 5 to 7 years at best, depending on the exposure location. A somewhat d i f f e r e n t approach was developed here i n order to protect transparent PVC against weathering ; i t consists i n applying at the surface of the PVC plate a t h i n coating that w i l l both exhib i t a high p h o t o s t a b i l i t y and be able to screen out the UV portion of the sunlight which has the most harmful e f f e c t s toward PVC (15). Such coatings can be r e a d i l y obtained by light-induced polymerizat i o n of multifunctional a c r y l i c monomers (16). The highly c r o s s l i n ked polymer network thus formed was shown T j 7 ) to r e s i s t UV radiation and chemicals very w e l l , while i t exhibits at the same time remarkable mechanical properties. Therefore, an additional advantage that can be expected from this method of s t a b i l i z a t i o n l i e s i n the new surface properties which w i l l be confered to the coated material, i n p a r t i c u l a r a better resistance to scratching, abrasion and environmental attack. 1. UV-curing_of_acr^lic_monome The basic p r i n c i p l e of the light-induced polymerization of multifunctional monomers can be represented schematically as follows: INITIATOR

PHOTON

CROSSLINKED POLYMER

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

15.

DECKER

Photochemical Modifications of

PVC

213

Under UV i r r a d i a t i o n , the p h o t o i n i t i a t o r cleaves into r a d i c a l frag­ ments that react with the v i n y l double bond and thus i n i t i a t e the polymerization of the monomer. I f the l a t t e r molecule contains at least two reactive s i t e s , the polymerization w i l l develop i n three dimensions to y i e l d a highly crosslinked polymer network. The p h o t o i n i t i a t o r selected for this study was 1-benzoyl cyclohexanol (Irgacure 184 from Ciba Geigy), a compound known f o r i t s high i n i t i a t i o n e f f i c i e n c y and the wealc-coloration of i t s photoproducts. The multifunctional monomer was an epoxy-diacrylate d e r i ­ vative of bis-phenol A (Ebecryl 605 from UCB). A reactive diluent, tripropyleneglycol d i a c r y l a t e , had to be introduced i n equal amounts, i n order to lower the v i s c o s i t y of the formulation to about 0.3 Pa.s. When this r e s i n was exposed as a t h i n f i l m to the UV radia­ t i o n of a medium pressure mercury lamp (80 W cm~1), the c r o s s l i n k i n g polymerization was found to develop extensively within a f r a c t i o n of a second (18). The kinetic wed q u a n t i t a t i v e l y by monitorin at 810 cm" of the a c r y l i twisting) Figur shows a t y p i c a l k i n e t i c curve obtained f o r a 20 ym thick f i l m coated onto a NaCl disk and exposed i n the presence of a i r to the UV radia­ t i o n at a fluence rate of 1.5 χ 10"6 e i n s t e i n s"1 cm" . 1

2

The induction period observed at the very beginning of the i r r a d i a t i o n i s due to the well known i n h i b i t i o n e f f e c t of oxygen on these radical-induced reactions. Once i t i s over, a f t e r the ^10 ms needed to consume e s s e n t i a l l y a l l of the oxygen dissolved i n the l i q u i d f i l m (19), the polymerization s t a r t s r a p i d l y to reach 75 % conversion witïïin 0.08 s. Further UV exposure leads only to a slow increase i n the cure, mainly because o f m o b i l i t y r e s t r i c t i o n s i n the r i g i d matrix, so that there s t i l l remains about 15 % of a c r y l i c unsaturation i n coatings heavily i r r a d i a t e d for 0.4 s. In order to act as an e f f i c i e n t anti-UV f i l t e r , the coating must absorb e s s e n t i a l l y a l l the UV r a d i a t i o n of λ < 380 nm from the solar spectrum. Therefore, an hydroxy-benzotriazole UV absorber (Tinuvin 900 from Ciba Geigy) was introduced i n small amounts (0.5%) in the formulation before curing, which allows a good dispersion of this additive i n the l i q u i d r e s i n . As expected, the rate of the photopolymerization i s then dropping s u b s t a n t i a l l y (figure 8), since the UV absorber now competes with the p h o t o i n i t i a t o r f o r the absorp­ t i o n of the incident l i g h t . Under the experimental conditions used, extensive through cure was s t i l l achieved within less than one se­ cond of exposure to the UV lamp. When the p h o t o s t a b i l i z a t i o n of a polymer material i s to be obtained through such a surface treatment process, i t i s a l l impor­ tant to make sure that the protective e f f e c t w i l l l a s t throughout the service l i f e and therefore to ensure a long-term adhesion of the coating onto the substrate. This can be best achieved by promoting a g r a f t i n g reaction between the two elements (20). For that purpose, the p h o t o i n i t i a t o r was p a r t l y incorporated i n the top layer of the PVC plate by a surface treatment with an acetone s o l u t i o n . Upon UVi r r a d i a t i o n of the resin-coated sample, the following reactions are expected to occur :

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

214

CHEMICAL REACTIONS ON POLYMERS

Coated

Carbon

Pattern

F i g u r e 7. Schematic r e p r e s e n t a t i o n o f t h e o v e r a l l l a s e r - c a r b o n i z a t i o n p r o c e s s o f PVC

Conversion

(%)

1001—

0

0.05

Irradia

0.10

t ion-tim

e

0.15

(second)

F i g u r e 8. K i n e t i c s o f t h e p h o t o p o l y m e r i z a t i o n o f an epoxy d i a c r y l a t e r e s i n w i t h and w i t h o u t UV a b s o r b e r (0.5 % o f T i n u v i n 900)

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

15.

Photochemical Modifications of PVC

DECKER

%CH2-0

+

CH-C-0

CH

;

o

CI

215

O - C - C H = CE II

0

S

ο S

The i n i t i a t o r radicals formed by photocleavage at the poly­ mer surface are most l i k e l y to abstract an hydrogen atom from the surrounding PVC molecules to generate PVC radicals at the r e s i n polymer interface. By reacting with the a c r y l i c double bonds of the monomer, these radicals w i l l then i n i t i a t e the crosslinking polyme­ r i z a t i o n leading ultimately to a polymer network that i s grafted on­ to the PVC support. As a consequence of this chemical bonding taking place at the interface, the adhesion of the a c r y l i c coating onto the PVC substrate was much improved and found to remain e s s e n t i a l l y unchanged a f t e r photoaging (20). 2

· Light stabilU^ z

Previous studies on the photooxidation of UV cured epoxyacrylate networks have revealed the remarkable resistance of these polymers to UV radiation (17). The quantum y i e l d s of the various rea­ ctions that occur upon photoaging were found to be considerably l o ­ wer than i n l i n e a r polymers o f s i m i l a r chemical structure. This outstanding l i g h t - s t a b i l i t y r e s u l t s e s s e n t i a l l y from the high cross­ l i n k density of the network which, by decreasing the molecular mo­ b i l i t y , i s expected to favor cage-recombination of the primary r a d i ­ cals over chain propagation. Even a f t e r prolonged UV exposure, no s i g n i f i c a n t changes could be noticed i n both the o p t i c a l properties (color, transparency, glass) and the mechanical c h a r a c t e r i s t i c s o f these crosslinked polymers. It was therefore tempting to use such UV resistant materials as protective coatings i n order to improve the l i g h t - s t a b i l i t y of a photosensitive polymer l i k e PVC. Transparent PVC plates were coated with a 70 ym thick f i l m of an epoxy-aerylate r e s i n containing 0.5 % o f a benzotriazole UV absorber. They were f i r s t UV cured f o r one second and then exposed at 40°C to the low i n t e n s i t y radiations o f a QUV accelerated wea­ thering t e s t e r . The extent of the degradation was followed by UVv i s i b l e spectroscopy, a very sensitive method that permits detec-

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

216

t i o n of minor changes i n the d i s c o l o r a t i o n which usually precedes the f a i l u r e i n the mechanical properties of photodegraded PVC. F i ­ gure 9 shows the absorption spectra of the uncoated PVC samples, before and after QUV aging. The 2 mm thick PVC transparent plate used here was a commer­ c i a l material, w e l l s t a b i l i z e d with t i n maleate and benzotriazole additives. I t nevertheless proved to be quite susceptible to photodegradation since, a f t e r 500h of QUV exposure, the PVC plate becames heavily colored, as shown by the strong absorption i n the v i s i b l e range due to the formation of long conjugated polyene sequences. At that time, chain s c i s s i o n and crosslinking have occured to a large extent, which leads to both a loss i n transparency and a sharp drop in the impact resistance of the i r r a d i a t e d sample. By contrast, the coated PVC plate was found to be l i t t l e affected by QUV aging (figure 9) ; even after 1000h of exposure, i t s t i l l remained e s s e n t i a l l the v i s i b l e range. By measurin ple at 420, 580 and 680 , yello (YI) from the following equation : ( T

YI

o " V420 "

i

T

o " V680

(τ ) 580 ο

where T and T correspond to the transmission of the sample at the indicated wavelength, before and after i r r a d i a t i o n during time t , respectively. In the case of transparent PVC, the yellow index i s generally considered as the best parameter to assess the extent of the degradation. o

t

The s t a b i l i z i n g e f f e c t of the coating i s well demonstrated by f i g . 10 which shows the k i n e t i c s of the d i s c o l o r a t i o n upon aging i n a QUV weatherometer. For the uncoated PVC plate, i t takes about 400h of exposure to reach a yellow index of 10, a value which i s usually considered as the upper l i m i t acceptable f o r outdoor a p p l i ­ cations. For the coated PVC on the contrary, no d i s c o l o r a t i o n was detected after 400h and the yellow index stayed well below 10 after more than 2000h of QUV exposure. Similar results were obtained by photoaging i n a weatherometer where i t took over 10,000h of exposure f o r the coated PVC to reach a YI value of 10. I f a comparable impro­ vement i n the l i g h t s t a b i l i t y i s observed i n the natural weathering experiments now i n progress, one can expect by this surface t r e a t ­ ment to considerably increase the outdoor d u r a b i l i t y of transparent PVC. A c t u a l l y i t appears that such an important s t a b i l i z i n g e f f e c t i s mainly due to the presence i n the coating of the UV absorber which i s e f f e c t i v e l y cutting o f f a l l the harmful radiations of wa­ velength below 380 nm. Under the experimental conditions used, i t was indeed shown that the benzotriazole l i g h t - s t a b i l i z e r i s 20 times more e f f i c i e n t i n preventing the absorption of l i g h t by the PVC substrate when i t i s acting as an external f i l t e r than i f i t i s d i s ­ persed i n the bulk of the polymer. Another advantage of introducing the UV absorber i n the crosslinked coating i s that the loss of sta­ b i l i z e r by exudation during the aging i s considerably reduced since

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Photochemical Modifications of PVC

Figure 9. UV-visible absorption spectra of a s t a b i l i z e d PVC plate, with or without a 70 ym UV cured epoxy-aerylate coating , before and after QUV aging at 40°C

QUV,

40°C

PVC

2000

1000 Exposure

time

(hours)

Figure 10. Kinetics of the discoloration of a 2 mm plate of s t a b i l i z e d PVC, with or without a 70 ym epoxy acrylate coating upon QUV aging at 40°C

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these molecules are trapped within a t i g h t network and are therefore much less l i k e l y to migrate toward the surface of the coating. In this connection, i t should be mentioned that, when p l a s t i c i z e d PVC was used instead of r i g i d PVC as a support, the highly-crosslinked coating acted as an e f f i c i e n t s u p e r f i c i a l b a r r i e r that prevents the p l a s t i c i z e r from d i f f u s i n g out of the PVC substrate. F i n a l l y , i n addition to t h e i r photoprotective action, such UV-cured coatings also impart new surface properties to the coated polymer. Since the epoxy-aerylate network i s s t r i c t l y insoluble i n the organic solvents and even suffers very l i t t l e swelling, the coated PVC plate becomes insoluble i n solvents l i k e dichloroethane or tetrahydrofuran. Furthermore, i t was found quite resistant to a c i d i c pollutants, moisture, saline vapors , at temperatures up to 70°C. The coated PVC samples also show a better resistance to abrasion and scratching and exhibit a high gloss, even after extended photoaging. Therefore, such transparent polymer materials are most l i k e l y to be used as lo tions i n the building industr is highly required, together with good mechanical and o p t i c a l properties.

REFERENCES 1. E. Owen "Degradation and stabilization of PVC" Elsevier Appl. Sci. Publ. London 1984 2. R.H. Baughman, J.L. Bredas, R.R. Chance, R.L. Eisenbaumer, L.W. Shacklette Chem. Rev. 82, 209 (1982) 3. G.L. Baker, Polym. Mat. Sci. Eng. 55, 77 (1986) 4. C. Decker and M. Balandier, J. Photochem. 15, 213 (1981) 5. C. Decker and M. Balandier, J. Photochem. 15, 221 (1981) 6. Kise, H, Sugihara, M and H.E., F.F., J. Appl. Polym. Sci. 30, 1133 (1985) 7. C. Decker and M. Balandier, Makrom. Chem. 183, 1263 (1982) 8. C. Decker, M. Balandier and J. Faure, J. Macromol. Sci. A16, 1463 (1981) 9. C. Decker, M. Balandier and J. Faure, 27 Intern. Symp. on Macromolecules Strasbourg 1981, Preprints vol. 1, p. 445 10. M. Balandier, J. Faure and C. Decker, FR-Patent 2.492.387 (1982) 11. C. Decker and M. Balandier, Polym. Photochem. 5, 267 (1984) 12. R.K. Friedlina "Advances in Free-Radical Chemistry" (Edited by G. Williams) vol. 1, chap. 6, Logos, London (1965) 13. C. Decker J. Polym. Sci., Polym. Letters, 25, 5 (1987) 14. M.S. Dresselhaus and G. Dresslhaus, Advances in Physics, 30, 139 (1981) 15. C. Lorenz,S. Tu and P. Wyman, US Patent 4.129.667 (1978) and 4.135.007 (1979) 16. C.G. Roffey "Photopolymerization of surface coatings" John Wiley New-York 1982 17. T. Bendaikha and C. Decker, J. Radiation curing, 11, 6 (1984) 18. C. Decker and T. Bendaikha, Europ. Polym. J. 20, 753 (1984) 19. C. Decker and A. Jenkins, Macromolecules 20. C. Decker, J. Appl. Polym. Sci. 28, 97 (1983) RECEIVED August

27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter

16

Hydrophilization of Polydiene Surfaces by Low—Temperature Ene Reactions Lee A. Schechtman Procter & Gamble Company, Miami Valley Laboratories, P.O. Box 39175, Cincinnati, OH 45247

The low temperatur triazoline-3,5-dione surfaces. Hydrophilic surfaces (contact angles with water of 30-50°) were obtained on polybutadiene, polyisoprene and styrene-butadiene copolymers by first treating the polymer at room temperature with RTD (R=Ph, Me, NOPh, ClSO Ph) and then with aqueous base. The use of the difunctional bis(p-1,2,4-triazoline-3,5-dione-4-ylphenyl)methane, (TD)DPM, also produced hydrophilic surfaces. However, except for the (TD)DPM treated surfaces, the hydrophilicity of the treated surfaces decreased after 5-10 days. The (TD)DPM surfaces are presumably crosslinked and remain hydrophilic for at least one year. The degree of reaction, as indicated by contact angle measurements, obtained under these heterogeneous reaction conditions suggest that the relative reactivity of the various RTDs and polydienes parallel the analogous reactions under homogeneous conditions. An ESCA study of ClSOPhTD treated surfaces confirms that the RTD is a surface species. The transformations of the surface species upon treatment with warm water and then aqueous base, -SO Cl --> -SO H --> -SO3-, were also substantiated by ESCA. 2

2

2

2

2

2

2

3

For many applications the surface properties of a polymer are of equal or greater importance than the polymer's bulk properties. Properties such as w e t t a b i l i t y (1) adhesion (2^_3) permeability (4·) biocompatibility (5), or weatherability (6) of polymer surfaces may be key considerations i n evaluating a polymer's s u i t a b i l i t y for a given need. To promote adhesion i t i s usually desirable to have surfaces of high surface energy (2). Since many synthetic polymers have r e l a t i v e l y low surface energies (_7), a number of methods have been devised to increase the surface energy of polymers ( i . e . , to make the surface hydrophilic without making the polymer water soluble or swellable). Methods currently used for the hydrophilization of polymer surfaces include chemical modification (8), plasma modification (9), 0097-6156/88/0364-0219S06.00/0 © 1988 American Chemical Society

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and i r r a d i a t i o n methods (10). Chemical modification can cause degradation of the polymer molecules at the surface (8), although i n some cases polymer degradation i s not observed (11,12). Plasma methods can result i n surface degradation or surface grafting depending on whether a reactive gas, inert gas, or polymerizable gas i s used to generate the plasma as well as other experimental conditions (9). Despite the many unique surface properties obtainable with plasma methods, they are not yet employed widely i n large scale commodity processing. While i r r a d i a t i o n methods can be used to modify surfaces (e.g., graft polymerization), they may suffer from simultaneous modification of bulk polymer and the d i f f i c u l t y of getting homogeneously covered surfaces (9,10). Thus, surface modification methods that are mild, uniform, and nondestructive are desirable. Of particular interest to us was to find a method to surface modify elastomers. G. B. Butler and co-workers have demonstrated that 4-substituted-l,2,4-triazoline-3,5-diones ene reactions with polydiene found that the s o l u b i l i t y propertie

polymers, 1_, are quite different from those of the parent polymer. Furthermore, neutralization of the pendant urazole on _1 produced 2_ which has s t i l l different solution properties. I f the degree of substitution i s greater than 40%, then 2 i s water soluble (14). The degree of substitution depends on the r a t i o of RTD to monomer units up to degrees of substitution of 1 (15).

Bis-triazolinedione compounds such as b i s ( p - l , 2 , 4 - t r i a z o l i n e 3,5-dione-4-ylphenyl)methane, (TD)2 PM, have been used to crosslink D

(TD) DPM 2

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rubbers (15-17) . Dipping natural rubber into solutions of (TD)2DPM causes surface hardening of the rubber (17). Triazolinediones have also been used to treat rubber surfaces to promote adhesion (18). However, these investigators did not subsequently neutralize the surfaces. This investigation was undertaken to study the important variables i n the hydrophilization of polydiene surfaces by ene reaction with triazolinediones (Step 1) followed by neutralization (Step 2) as shown below. These variables included the nature of the

ο

'\

Step 1^

7

Ο

ο

H N

Step 2 ^

Y

-τι

polydiene double bond, the nature of R i n RTD, and experimental conditions such as reaction time and RTD concentration. Experimental Reagents. Published procedures were used to synthesize PhTD (19), MeTD (19), and p-ClS02PhTD (20) from commercially available urazoles (Aldrich, A l f a ) , while (TD) DPM (17) and p-N0 PhTD (19) were prepared from the appropriate isocyanates. The RTDs were p u r i f i e d by sublimation, except for (TD)2 PM which was p u r i f i e d by p r e c i p i t a t i o n or used as the synthesis product after vacuum drying. The polydienes used were purchased (Aldrich, Polyscience) and used as received except for cis-polyisoprene which was p u r i f i e d by p r e c i p i t a t i o n . These polydienes are l i s t e d i n Table I. The 3,3-ionene hydroxide used i n some of the neutralization experiments was prepared from 3,3-ionene chloride (21) by passage through an ion exchange column i n the hydroxide form or treatment with Ag20 (22). A l l solvents used were reagent grade and were t y p i c a l l y dried over activated molecular sieves. 2

2

D

Table I.

Polymers and Abbreviations Abbreviation

Polymer b

trans-polybutadiene cis-polybutadiene cis-polyisoprene trans-polyisoprene styrene/butadiene ABA block copolymer

t-PB c-PB c-PI t-PI

160,000 300,000 2,000,000

0

a

Determined by ultracentrifuge for PB samples and l i g h t scattering for PI. t-PB contained 60% trans, 20% c i s , 30% styrene. and 20% 1,2-addition. b

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Polymer Films» The polymer films were prepared by casting 5% toluene solutions onto glass microscope s l i d e s . After a i r drying i n a fume hood, the films were vacuum dried. Film thicknesses were t y p i c a l l y 0.05 mm. Surface Modification. A polydiene f i l m (supported on a microscope s l i d e ) was immersed i n a s t i r r e d , room temperature, RTD-acetonitrile solution of known concentration contained i n a large glass-stoppered test tube. After a s p e c i f i c reaction time, the film was removed from the solution, washed with a c e t o n i t r i l e , water, and a c e t o n i t r i l e again, and dried under vacuum (Step 1). Films subsequently treated with base were immersed i n aqueous solutions for 5-15 min. They were then washed with water and CH3CN, and vacuum dried (Step 2). Some films were aged i n a i r at room temperature. A n a l y t i c a l Techniques. Sessile drop contact angles were measured with a NRL C.A. Goniometer (Rame'-Hart, Inc.) using t r i p l y d i s t i l l e d water. The contact angle reported f 2-8 i d e n t i c a l l treated samples with at sample. ESCA spectra wer Photoelectron Spectrometer under the control of a DS-300 Data System. Peak area measurements and band resolutions were performed with a DuPont 310 Curve Resolver. Results and Discussion Polydiene surfaces treated with PhTD or MeTD and then with base are rendered more hydrophilic than the untreated polymer. Typical values of the contact angle of water with the treated surfaces are given i n Table I I . The values are given as ranges because there was a wide scatter i n the data from one sample to another although great care was exercised to make handling of duplicate samples as uniform as possible. Since contact angle measurements are very sensitive to surface heterogeneity, i t i s not surprising to see such discrepancies (23,24). The untreated polymers give water contact angles of 90°. A t-PB/PhTD 1:1 polymer prepared as described by Leong and Butler (14) and cast from DMF has a contact angle of 65°. Of course treatment of this polymer with base resulted i n complete dissolution of the f i l m . Table I I .

Contact Angles (H2O)

Polymer

PhTD 1

t-PB c-PB c-PI t-PI

of Treated Polydiene F i l m s

75-80 75-90 60-65 50-65

MeTD 2 50-75 70-80 25-60 30-45

1

2

80-90 80-84 59-88 52-68

60-80 65-80 30-90 20-50

a

Contact angles are i n degrees; values are given as ranges which r e f l e c t the s e n s i t i v i t y of contact angle to surface heterogeneity after Step 1 and Step 2 (see experimental) for PhTD and MeTD. Reaction times were 5-60 s i n RTD solutions of 0.2-0.5 M.

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When the reaction times for Step 1 are 5 min or longer, the samples severely crack, c u r l , or dissolve. These r e s u l t s suggest that substantial reaction i s occurring i n the bulk of the polymer. Significant hydrophilization can occur with reaction times as short as 5 s with RTD concentrations of 0.2-0.5 M. However, 0.002-0.02 M solutions of MeTD or PhTD do not allow s u f f i c i e n t reaction rates for surface hydrophilization at the shorter reaction times. Thus, d i f f u s i o n of MeTD and PhTD into the polymer must occur r e a d i l y from the a c e t o n i t r i l e solutions. A c e t o n i t r i l e was used because i t does not swell or dissolve the polymer or RTD-polymer adduct, and the RTDs are soluble and stable i n i t . This solvent i s quite polar ( d i e l e c t r i c constant, £=38) (25), and t h i s i s probably a major factor i n the p a r t i t i o n i n g of the r e l a t i v e l y nonpolar RTDs between the polydiene f i l m and the solvent. As noted below, more polar RTDs show less tendency to diffuse into the polymer. The most hydrophilic surfaces are obtained with the polyisoprenes and PhTD. Since the reactio time quit short thi increased h y d r o p h i l i c i t y i s most l i k e l reaction of surface s i t e with homogeneous ene reaction r e a c t i v i t i e s . Two factors favor polyisoprenes being more reactive than polybutadienes i n ene reactions. F i r s t , primary hydrogens, which PI has but PB does not, are abstracted more readily than secondary hydrogens (26). Second, t r i a l k y l substituted double bonds, such as those i n PI, are i n general more reactive toward enophiles than 1,2-disubstituted double bonds, such as those i n PB (27). Also, PhTD i s a more reactive enophile than MeTD by v i r t u e of the greater electron-withdrawing e f f e c t of the phenyl ring vs. the methyl group (28). Significant hydrophilization of c-PI surfaces with NO2PhTD (0.2 M) could be achieved with reaction times of 1-15 s (contact angle 52°). The n i t r o group makes this an extremely reactive TD (28). Also, the increased p o l a r i t y of the molecule was expected to make i t s d i f f u s i o n into the polymer less favorable. However, reaction times greater than 1 min do result i n films that crack or c u r l . This i s indicative of reaction within the bulk of the sample. Because of i t s high r e a c t i v i t y , N0 PhTD was d i f f i c u l t to purify and work with. In contrast, ClS02PhTD d i d not show a tendency to migrate into the bulk of the polymers. When t-PB was treated with a ClS02PhTD solution (0.001 M) f o r 20 h, a contact angle of 70° was measured. . After being placed i n water (50 °C, 1 h) and then dried, the sample had a contact angle of 64°. Neutralization of the sample with aqueous NaOH (1 M) resulted i n a f i l m having a contact angle of 36°. Thus, a long reaction time at a low concentration of RTD (conditions that should favor substantial migration of RTD into the polymer) did not result i n cracked, curled or soluble polymer f i l m . An ESCA angular depth p r o f i l e study of s i m i l a r l y treated t-PB showed that sulfur and nitrogen are surface species. Figure 1 shows the chemical transformations occurring during this sequence of treatments based on the reactions of analogous nonpolymeric model compounds (20). The ESCA spectra of the polymer films taken a f t e r each transformation also support this scheme, Figure 2. The high resolution spectra of species _5 and 6^ show N(ls) peaks at 401 eV (nonprotonated nitrogen) and 402.7 eV (protonated nitrogen) while samples neutralized with base, _7, do not show protonated nitrogen peaks. Also, the l a t t e r sample shows two species 2

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Figure 1.

Treatment sequence of samples examined by ESCA.

—l

800

1

600

1

400

1—

200

B i n d i n g E n e r g y (eV)

Figure 2.

ESCA Spectra of t-PB, 5, 6, and 7.

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of sodium. The Cl(2p) peak (199.5 eV) indicates a large abundance of CI for J5. No chlorine i s detected for the base treated samples, _7. Interestingly, the i n t e n s i t y of the S(2p) peak (168 eV) decreases i n each sample along the progression of treatment, J>""*j>""'2.' This suggests that the some of the surface i s removed during each step. Difunctional (TD)2DPM was another reagent that could be used at low concentrations and long reaction times while giving only surface modification. Treatment of c-PI and c-PB i n 0.01 M (TD^DPM solution for 24 h produced films with 30° contact angles after n e u t r a l i z a t i o n . Presumably the added size of this reagent and i t s a b i l i t y to c r o s s l i n k the polymer greatly slows i t s d i f f u s i o n within the polymer. Another advantage of this reagent i s that the hydrophilic surfaces produced by i t show only a small loss of h y d r o p h i l i c i t y on aging. Most of the surfaces hydrophilized with mono-TD reagents showed losses i n h y d r o p h i l i c i t y after 5-10 days; contact angles rose to 70-90°, Figure 3. The increase i n contact angle i s due to rearrangement of the surfac migrate to the surface. thermodynamically favored over high energy surfaces (29). Also, entropie factors are expected to favor the mixing of the urazole groups on the surface into the bulk polymer. Such factors have been shown to be important i n surface modified polymers that are above or near their Tg (29). Alternate explanations for the loss of h y d r o p h i l i c i t y upon aging include the blooming of hydrophobic impurities i n the polymer to the surface (30), or the deposition of ubiquitous airborne contaminants onto the surface. However, since the (TD)2 PM surfaces can remain r e l a t i v e l y hydrophilic for up to 1 year, these are probably not s i g n i f i c a n t factors i n the loss of h y d r o p h i l i c i t y . I t should be noted that oxidized polydiene films (exposed to a i r 1 year) can display contact angles as low as 65°. Better surface s t a b i l i t y could be achieved i f the surface components are less mobile. Some success has been achieved with polyethylene and perhalogenated polymer surfaces (8,11,12,29). Crosslinking the surface should also decrease i t s mobility, and t h i s i s how (TD)2DPM provides added s t a b i l i t y , Figure 3. Some surface rearrangement does appear to occur i n i t i a l l y , but samples have retained good h y d r o p h i l i c i t y (contact angle 45-55°) for a year. In order to obtain stable hydrophilic surfaces with (TD)2 PM i t i s necessary to use i t at the low concentration and long reaction time described above. Polydienes treated with 0.1 M solutions of (TD)2DPM for 3 h did show good h y d r o p h i l i c i t y (contact angle 35°) initially. However, the h y d r o p h i l i c i t y of the surfaces decreased s i m i l a r l y to those of PhTD treated surfaces. Apparently, the higher concentration of reagent favors the reaction of the surface double bonds, with d i f f e r e n t (TD)2DPM molecules which r e s u l t s i n l i t t l e or no c r o s s l i n k i n g . Whereas, the lower concentration of reagent allows time for a (TD)2DPM molecule to react at one end and then s t i l l find double bonds available to react with the remaining TD end. The net result i s c r o s s l i n k i n g . Attempts to obtain permanently hydrophilic surfaces by other types of c r o s s l i n k i n g chemistry were not successful. The other methods investigated included forming ionic c r o s s l i n k s , using cured e

D

D

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10

20 T i m e (Days)

Figure 3. Contact angle vs. time for PB treated with PhTD (·) and PI treated with (TD>2DPM (•). Both neutralized with NaOH.

Figure 4. Contact angle vs. time for PB treated with PhTD and neutralized with 3,3-ionene hydroxide (•), styrene-butadiene ABA block copolymer treated with PhTD and neutralized with NaHC03 (·), and PI treated with PhTD and neutralized with CaO (A).

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polymers as substrates, or using block copolymers. By using a base with a polyvalent cation, one might hope to achieve crosslinking through ionic interactions (31). The use of CaO i n place of NaOH did not enhance the permanence of PhTD treated surfaces. The use of 3,3-ionene hydroxide, Figure 4, did not provide good h y d r o p h i l i c i t y even i n i t i a l l y (contact angle 70°). Currently, the explanation for this behavior i s not known. A so called "hydrophobic e f f e c t " , resulting from the conformation of the ionene on the surface, may be operative. The use of l i g h t l y crosslinked polymers did result i n hydrophilic surfaces (contact angle 50°, c-PI, 0.2 M PhTD). However, the surfaces displayed severe cracking after 5 days. Although q u a l i t a t i v e l y they appeared to remain hydrophilic, r e l i a b l e contact angle measurements on these surfaces were impossible. Also, the use of a styrene-butadiene-styrene t r i b l o c k copolymer thermoplastic elastomer did not show improved permanence of the h y d r o p h i l i c i t y over other polydienes treated with PhTD Th block copolyme fil cast from toluene, and transmissio the continuous phase wa Both polystyrene and polybutadiene domains are present at the surface. This would probably l i m i t the maximum h y d r o p h i l i c i t y obtainable since the RTD reagents are not expected to modify the polystyrene domains. Conclusions The low temperature ene reaction of triazolinediones with polydienes occur under heterogeneous conditions to y i e l d hydrophilic surfaces, especially after neutralization of the resulting pendant urazole groups. Permanent hydrophilic surfaces can be obtained when (TD)2DPM i s used. The use of the other RTDs tested results i n surfaces that lose their h y d r o p h i l i c i t y within 5-20 days. In applications such as improving the adhesion of rubber to other substrates, these reagents are probably s u f f i c i e n t (18). However, when more permanent hydrophilic surfaces are desired a b i s triazolinedione such as (TD)2DPM would be required. Acknowledgment s Most of the sample preparations and contact angle measurements were made by A. D. Karnas. K. W. Littlepage and G. G. Engerholm did the ESCA spectroscopy. J. Burns did the electron microscopy on the block copolymers. I thank D. F. Hager and G. B. Butler for h e l p f u l discussions.

Literature Cited 1. Zisman, W. A. In Adhesion Science and Technology; Lee, L.-H., Ed; Plenum: New York, 1975; p. 55. 2. Huntsberger, J. R. In Contact Angle, Wettability, and Adhesion; Fowkes, F. M., Ed.; Advances in Chemistry Series No. 43; American Chemical Society: Washington,D. C., 1964; Chapter 7. 3. Andrew, Ε. H.; King, Ν. E. In Polymer Surfaces; Clark, D. T.; Feast, W. J., Eds.; John Wiley & Sons: New York, 1978; Chapter 3.

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4. Bixler, J. J.; Sweeting, O. J. In The Science and Technology of Polymer Films, Vol. II; Sweeting, O. J., Ed.; WileyInterscience: New York, 1971; Chapter 1. 5. Lyman, D. J. Angew. Chem. Int. Ed. Engl. 1974, 13, 108. 6. Carlsson, D. J.; Wiles, D. M. J. Macromol Sci., Rev. Macromol. Chem. 1976, 14, 65. 7. Shafrin, E. G. In Polymer Handbook, 2nd ed.; Brandrup, J.; Immergut, Ε. H., Eds.; Wiley-Interscience: New York, 1975; p. III-221. 8. Rasmussen, J. R.; Stedronsky, E. R.; Whitesides, G. M. J. Am. Chem. Soc. 1977, 99, 4736. 9. Yasuda, H. J. Polym. Sci., Macromol. Rev. 1981, 16, 199. 10. Tazuke, S.; Kimura, H. Makromol. Chem. 1978, 179, 2603. 11. Dias, A. J.; McCarthy, T. J. Macromolecules 1985, 118, 1826. 12. ibid. 1984, 17, 2529. 13. Butler, G. B. Ind. Eng. Chem. Prod. Res. Dev. 1980, 19, 512. 14. Leong, K.-W.; Butler G B J. Macromol Sci. Chem 1980 A14 287. 15. Butler, G. B.; Williams Polym Polym 1979, 17, 1117. 16. Rout, S. P.; Butler, G. B. Polym. Bull. 1980, 2, 513. 17. Saville, B. J. Chem. Soc., Chem. Commun. 1971, 635. 18. Cutts, E.; Knight, G. T. U.S. Patent 3 966 530, 1976. 19. Stickler, J. C.; Pirkle, W. H. J. Org. Chem. 1966, 31, 3444. 20. Keana, J. F. W.; Guzikowski, A. P.; Ward, D. D.; Morat, C.; VanNice, F. L. J. Org. Chem. 1983, 48, 2654. 21. Yen, S. P. S.; Casson, D.; Rembaum, A. In Water Soluble Polymers; Bikales, Ν. M., Ed.; Plenum: New York, 1973; p. 291. 22. Razvodovskii, E. F.; Nekrasov, Α. V.; Enikolopyam, N. S. Vysokomol. Soedin., Ser. B. 1972, 14, 338; Chem. Abstr. 1972, 77, 75533z. 23. Dwight, D. CHEMTECH 1982, 12, 166. 24. Adamson, A. W.; Ling, I. In Contact Angle, Wettability, and Adhesion; Fowkes, F. M., Ed.; Advances in Chemistry Series No. 43; American Chemical Society: Washington, D.C.; 1964, Chapter 3, p. 69. 25. Bates, R. B.; Schaefer, J. P. In Research Techniques in Organic Chemistry; Prentice-Hall: Englewood, NJ 1971; p. 18. 26. Hoffmann, H. M. R. Angew. Chem. Int. Ed. Engl. 1969, 8, 556. 27. Snider, Β. B. Acc. Chem. Res. 1980, 13, 426. 28. Ohashi, S.; Butler, G. B. J. Org. Chem. 1980, 415, 3472. 29. Holmes-Farley, S. R.; Whitesides, G. M. Polym. Mater. Sci. Eng. 1985, 53, 127. 30. Brewis, D. M.; Briggs, D. Polymer 1981, 22, 7. 31. Kinsey, R. H. J. Appl. Polym. Chem., Appl. Polym. Symp. 1969, 11, 77. RECEIVED August

27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter

17

Surface Heparinization of Poly(ethylene terephthalate) Films Modified with Acrylic Hydrogels Cristofor I. Simionescu, Monica Leanca, and Ioan I. Negulescu "Petru Poni" Institute of Macromolecular Chemistry, Iaşi 6600, Romania A semi-interpenetrated network obtai ned by bulk thyl methacrylat incorporate F ated PET films by solvent-exchange techni­ que, followed by treatment of films i n e­ l e c t r i c a l discharges. Heparinization was accomplished by reacting glutaraldehyde with heparin and poly(2-hydroxyethyl me­ thacrylate) present on the surface of mo­ dified polyester films. The immobilization of heparin was i n d i r e c t l y evidenced by chromatographying the s i l y l a t e d hydrolyza­ tes of heparinized PET films and heparin, respectively. In v i t r o experiments demon­ strated the enhanced thromboresistance of heparinized films. More t h a n 20 y e a r s h a v e p a s s e d f r o m t h e f i r s t r e p o r t o f G o t t e t a l . ( 1 ) on t h e b o n d i n g o f h e p a r i n on c o l l o i d a l g r a p h i t e s u r f a c e a n d some h e p a r i n - c o n t a i n i n g m a t e r i a l s d e v e l o p e d s i n c e t h e n have f o u n d c l i n i c a l a p p l i c a t i o n s ( 2 ) . S u r f a c e m o d i f i c a t i o n has l o n g been seen as o f f e r i n g the advantage o f v e r y wide v a r i e t y i n t h e c h e m i c a l nature of the blood-presenting surface while a l l o w i n g the c h o i c e o f t h e s u b s t r a t e t o be on t h e b a s e s o f t h e mechan i c a l p r o p e r t i e s n e e d e d . The s u r f a c e m o d i f i c a t i o n i n c l u des t h e g r a f t i n g o f p o l y m e r s , s u c h a s m a c r o m o l e c u l a r h y d r o g e l s , w h i c h a r e i n h e r e n t l y t o o weak m e c h a n i c a l l y t o be u s e f u l a s u n s u p p o r t e d m a t e r i a l s . P o l y m e r s o f t h i s t y p e have b e e n e x t e n s i v e l y i n v e s t i g a t e d b o t h b e c a u s e t h e r e were e a r l y i n d i c a t i o n s t h a t poly(2-hydroxyethyl m e t h a c r y l a t e ) , pHEMA, p o s s e s s e d some d e g r e e o f t h r o m b o r e s i s t a n c e and because o f t h e h y p o t h e s i s t h a t a g e l s u r f a c e w o u l d be l e s s r e c o g n i z a b l e a s a f o r e i g n s u r f a c e t o the b l o o d ( 2 , 3 ) . P o l y m e r i c m a t e r i a l s w i t h c o v a l e n t l y imm o b i l i z e d h e p a r i n were shown t o d i s p l a y e n h a n c e d t h r o m 0097-6156/88/0364-0229$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

230

b o r e s i s t a n c e i n v i t r o arid i n v i v o e x p e r i m e n t s s i n c e t h e presence o f h e p a r i n s u b s t a n t i a l l y changes the c h a r a c t e r of a d s o r b e d p r o t e i n s on a p o l y m e r s u r f a c e a n d t h e number of a d h e r e d p l a t e l e t s ( 4 , 5 ) . The a i m o f t h i s p a p e r i s t o r e p o r t t h e b o n d i n g o f h e p a r i n on p o l y ( e t h y l e n e t e r e p h t h a l a t e ) f i l m s c o n t a i n i n g an a c r y l i c h y d r o g e l ( ρ H E M A ) , t h e method o f p r e p a r a t i o n of t h e s u p p o r t m a t e r i a l a n d some o f i t s p r o p e r t i e s . Experimental S t r i p s o f u n i d i m e n s i o n a l l y o r i e n t e d PET f i l m s (Terom, R o m a n i a ) o f 0 . 3 mm t h i c k n e s s , washed s u c c e s s i v e l y w i t h d e t e r g e n t s o l u t i o n , w a t e r a n d a c e t o n e , were t r e a t e d w i t h d i m e t h y l f o r m a m i d e , IMF ( P l u k a ) , a t v a r i o u s t e m p e r a t u r e s ( 5 0 - 1 4 0 ° C ) f o r 15 o r 30 m i n . The f i l m s were c e n t r i f u g a t e d and immersed i n mixtur f initiato (AIBK Serva) and monomer (HEMA, E a s t m a (2-100 h r ) . S u b s e q u e n t l f i l t e r p a p e r a n d i n t r o d u c e d i n g l a s s a m p o u l e s w h i c h were d e g a s e d , f i l l e d w i t h n i t r o g e n a n d s e a l e d . The a m p o u l e s were p u t i n a n o v e n a n d HEMA i n c o r p o r a t e d i n t h e p o l y e s ­ t e r m a t r i x was a l l o w e d t o p o l y m e r i z e a t 7 0 - 9 0 ° C f o r 5-48 h r . The f i l m s were t h e n s u b j e c t e d t o a n i t r o g e n g l o w d i s c h a r g e ( i n p u t power, 40 W; f r e q u e n c y , 2.5 MHz) a n d immersed t h e r e a f t e r f o r 35 m i n i n a n a q u e o u s a d h e s i v e mixture c o n t a i n i n g (6) p o l y v i n y l a l c o h o l (10%), g l y c e r i n (4%), magnesium c h l o r i d e (5%), h e p a r i n ( B i o f a r m - R o m a n i a , 5000 UI/mL) ( 1 % ) and g l u t a r a l d e h y d e ( 0 . 2 5 % ) . The m o d i f i ­ ed PET f i l m s d e s i g n a t e d a s c o n t r o l s a m p l e s were immersed i n a s i m i l a r mixture devoid of heparin. A f t e r d r y i n g f o r 5 h r a t room t e m p e r a t u r e t h e f i l m s were h e a t e d a t 8 0 ° C f o r 100 m i n a n d t h e n washed w i t h 3M N a C l s o l u t i o n f o r r e m o v i n g the u n r e a c t e d components, h e p a r i n i n c l u d e d . The s a m p l e s f o r g a s - c h r o m a t o g r a p h i c determinations were p r e p a r e d a c c o r d i n g t o I\ieeser e t a l . ( 7 ) a s f o l l o w s . Known amounts o f h e p a r i n i z e d f i l m s o r c o n t r o l s a m p l e s ( 0 . 5 g ) a n d h e p a r i n ( 0 . 0 1 g ) were h y d r o l y z e d i n s e p a r a t e e x p e r i m e n t s w i t h 4M CF-CG0H a t 125°C f o r 60 m i n . The h y d r o l y z a t e was d r i e d up by e v a p o r a t i o n , p y r i d i n e (1 mL) was a d d e d a n d t h e m i x t u r e was t r a n s f e r e e i n a r e a c t i o n tube c o n t a i n i n g methoxyamine h y d r o c h l o r i d e (0.003g) w h i c h was s u b s e q u e n t l y k e p t a t 80°G f o r 2 h r . N , 0 - b i s ( t r i m e t h y l s i l y l ) t r i f l u o r o a c e t a m i d e (0.2 mL) was i n t r o ­ d u c e d a f t e r c o o l i n g a n d t h e m i x t u r e was a l l o w e d t o r e a c t a t 8 0 ° C f o r 15 m i n . A d e t e r m i n e d volume (1 u L ) was i n ­ troduced t h e r e a f t e r i n gas-chromatograph (Practovap-M2350, C a r l o E r b a , e q u i p p e d w i t h F I D ; c o l u m n , SE-30). X - r a y m e a s u r e m e n t s were made a t room t e m p e r a t u r e u s i n g a TUR M-62 (DDR) s p e c t r o m e t e r . M e c h a n i c a l p r o p e r t i e s were d e t e r m i n e d a c c o r d i n g t o R o m a n i a n s t a n d a r d s u s i n g a n I n s t r o n 1114. The t h r o m b o r e s i s t a n c e o f f i l m s was d e t e r m i n e d i n v i t r o as the time o f b l o o d - c l o t t i n g .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

17.

SIMIONESCU E T AL.

Results

and

Surface Heparinization of PET Films

231

Discussion

The i n s i t u b u l k p o l y m e r i z a t i o n o f v i n y l monomers i n PET and the g r a f t p o l y m e r i z a t i o n o f v i n y l monomers t o PET are p o t e n t i a l useful tools f o r the chemical modification of t h i s polymer. The d i s t i n c t i o n between i n s i t u polymer i z a t i o n and graft polymerization i s a r e l a t i v e l y minor one, a n d f r o m a p r a c t i c a l p o i n t o f v i e w may be o f n o s i gnificance. I n graft p o l y m e r i z a t i o n , the newly formed polymer i s covalently bonded to a s i t e on the host polymer ( P E T ) , w h i l e the i n s i t u b u l k p o l y m e r i z a t i o n of a v i n y l monomer r e s u l t s i n a polymer that i s physically e n t r a p e d i n t h e P E T . The v i n y l p o l y m e r i z a t i o n i n t h e PET i s usually c a r r i e d out i n the presence of the swelling solvent, thereby m a i n t a i n i n g the swollen PET s t r u c t u r e d u r i n g p o l y m e r i z a t i o n . The s w o l l e n s t r u c t u r e allows the monomer t o d i f f u s e i s u f f i c i e n t quantitie t t t the active centers tha i n i t i a t i o n (with AIBE I t was shown ( 8 , 9 ) t h a t the pretreatment of PET yarns with c e r t a i n strongly i n t e r a c t i n g solvents can lead not only to swelling but also to i r r e v e r s i b l e modifications of polymers structure. The b a s i s of s t r u c t u r a l modificat i o n d u r i n g t h e DMF t r e a t m e n t of PET i s solvent-induced c r y s t a l l i z a t i o n which occurs while the PET s t r u c t u r e i s s w o l l e n by D M F . A t l o w t r e a t m e n t temperatures ( i . e . , 50-100°C, Table I ) , only small c r y s t a l l i t e s are formed and a f t e r removal of the solvent the swollen structure c a n n o t be s u p p o r t e d by t h e s m a l l c r y s t a l l i t e s and consequently collapses. Table

I .

Treatment Temp. Time (°C) (min)

Structural Parameters o f PET F i l m s Treat e d i n D M F a t D i f f e r e n t 'r e m p e r a t u r e s

Degree of Crystal. (%)

Untreated 50

15

100

30 15

32.7 35.5 37.1 42.1

15 30 15 30

44.7 47.5 55.4 54.7 57.3

50

100 120 120 140 140

30

Dimension of C r y s t a l l i t e s (X)

Amorphous Volume .Assoc. (A )

106.1 109.3 115.2 123.9

127.5 131.3 144.8 143.7 151.6

A s s h o w n i n F i g u r e 1 , w h e n t h e DMF t r e a t m e n t out at h i g h e r temperatures (120-140°C), the ty of the p o l y e s t e r increases and formation c r y s t a l l i t e s occurs (Table I ) . These larger stable c r y s t a l l i t e s are capable of supportin

3

163,200 159,750 146,350 132,470 127,327

114,655 105,979 107,830 97,270

i s c a r r c r y s t a l l of large a n d more g the s o

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

i e d i n i r l -

CHEMICAL REACTIONS ON

232

POLYMERS

v e n t - s w o l l e n s t r u c t u r e t o a g r e a t e r e x t e n t so t h a t t o t a l c o l l a p s e o f t h e s w o l l e n s t r u c t u r e upon removal o f t h e solvent i s prevented. V i n y l monomers c a n be i n t r o d u c e d i n t o t h e PET by two d i f f e r e n t p r o c e d u r e s . I n one p r o c e d u r e , t h e monomer i s i n t r o d u c e d i n t o t h e PET a f t e r r e m o v a l o f t h e DMF. I n t h e o t h e r p r o c e d u r e , t h e monomer i s s o l v e n t e x c h a n g e d w i t h t h e DMF i n t h e P E T . However, when DMF was r e m o v e d f r o m t h e PET p r i o r t o monomer i n c o r p o r a t i o n , l o w e r u p t a k e o f monomer was o b s e r v e d a s c o m p a r e d w i t h r e s u l t s o b t a i n e d by t h e s o l v e n t e x c h a n g e t e c h n i q u e ( 9 ) . C o n s e q u e n t l y t h e s o l v e n t e x c h a n g e t e c h n i q u e was u s e d i n t h e p r e s e n t work f o r t h e i n c o r p o r a t i o n o f HEMA i n t h e PET f i l m s . The d e p e n d e n c e o f t h e HEMA u p t a k e o n t h e t e m p e r a t u r e o f DMF t r e a t m e n t ( H E M A - s o l v e n t e x c h a n g e , 72 h r ) i s shown i n F i g u r e 2. I t c a n be s e e n t h a t o n l y i n t h e c a s e of DMF p r e t r e a t m e n t s at elevated temperatures when s o l vent-induced c r y s t a l l i z a t i o p l a c e , i s t h e monome t i m e d e p e n d e n c e o f HEMA i n c o r p o r a t i o n by D M F - t r e a t e d ( 1 4 0 ° C , 15 m i n ) PET f i l m s i s p r e s e n t e d i n t h e same f i g u r e . I t c a n be s e e n t h a t t h e p r o c e s s o f monomer i n c o r p o r a t i o n i s completed i n 60-70 h r . A c c o r d i n g l y , an e q u i l i b r a t i o n t i m e o f t h r e e d a y s was g e n e r a l l y a l l o w e d . P o l y m e r i z a t i o n o f HEMA i n c o r p o r a t e d i n t h e PET f i l m s i s dependent b o t h on t h e i n i t i a t o r c o n c e n t r a t i o n and r e a c t i o n t e m p e r a t u r e . I n o r d e r t o overcome t h e l o w i n i t i a t i o n e f f i c i e n c y i n s i d e t h e P E T , due t o t h e l o w mob i l i t y o f t h e f r e e r a d i c a l s f o r m e d i n s i d e t h e PET s t r u c t u r e , a s w e l l a s t h a t o f t h e monomer i t s e l f , h i g h i n i t i a t o r c o n c e n t r a t i o n s were u s e d . The r e s u l t s a r e l i s t e d i n T a b l e I I . However, s a t i s f a c t o r y c o n v e r s i o n s o f HEMA i n pHEMA were o b t a i n e d o n l y when t h e p o l y m e r i z a t i o n was c a r r i e d o u t a t 8 0 - 8 5 ° C f o r 20-40 h r , e v e n i f t h e i n i t i a t o r c o n c e n t r a t i o n was h i g h ( F i g u r e 3 ) . Table

II.

P o l y m e r i z a t i o n o f HEMA Incorporated i n PET F i l m s T r e a t e d i n DMF ( 1 4 0 ° C / l 5 m i n )

Incorporated HEMA, (%)

AIB'N i n HEMA (Mol/L)

20.8 20.8 20.8 20.8

0.03 0.06 0.08 0.10

Incorporated P o l y m e r , (%) 0.36 1.81 7.43 8.33

HEMA Conv e r s i o n , {%) 1.9 8.7 35.7 40.1

The i n c r e a s e o f t h e p o l y m e r i z a t i o n t e m p e r a t u r e t o 90 C r e s u l t e d i n a l o w monomer c o n v e r s i o n , d e s p i t e o f a l o n g e r r e a c t i o n t i m e ( 5 0 h r ) , p e r h a p s due t o t h e f a c t t h a t at t h i s temperature t h e p r o b a b i l i t y o f t e r m i n a t i o n r e a c t i o n s o f t h e newly formed f r e e r a d i c a l s i s v a s t l y i n creased ( 9 ) .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

17.

Surface Heparinization of PET Films

SIMIONESCUETAL.

I

1

ι

10°

ι

ι

ι

12°

ι

14°

1

1

16°

233

1

18° θ

F i g u r e 1. Wide a n g l e X - r a y d i f f r a c t i o n p a t t e r n f r o m PET f i l m s e x p o s e d t o DMP a t v a r i o u s t e m p e r a t u r e s f o r 15 m i n .

20 -ι

AO 1

60 1

80 1

100 T»me,hrs 1 1 r

Temperature, °C

F i g u r e 2. The d e p e n d e n c e o f HEMA i n c o r p o r a t e d i n PET f i l m s o n : / l / t h e t e m p e r a t u r e o f DMF t r e a t m e n t , a n d /2/ t h e t i m e o f i m m e r s i o n i n HEMA o f f i l m s t r e a t e d i n DMP a t 1 4 0 ° C f o r 15 m i n .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

234

CHEMICAL REACTIONS ON POLYMERS

When t h e ρHEMA c o n t a i n i n g PET f i l m s were s u b j e c t e d to n i t r o g e n g l o w d i s c h a r g e , t h e a c r y l i c p o l y m e r was g r a ­ f t e d t o t h e h o s t p o l y e s t e r (10,11), g i v i n g r i s e t o a s e ­ m i - i n t e r p e n e t r a t e d network s t r u c t u r e which i n c o n t a c t w i t h w a t e r a s s u r e s t h e f o r m a t i o n o f HEMA-based h y d r o g e l . B o t h t h e s o l v e n t t r e a t m e n t and pHEMA g r a f t i n g p r o c e s s e s determined a complete m o d i f i c a t i o n of the appearance of PET f i l m s , a n d i t c a n be s e e n f r o m t h e s c a n n i n g m i c r o ­ s c o p e i m a g i n e s shown i n F i g u r e 4. On t h e o t h e r h a n d , a c c o r d i n g t o t h e d a t a p r e s e n t e d i n T a b l e I I I , t h e mecha­ n i c a l p r o p e r t i e s o f pHEMA c o n t a i n i n g PET s a m p l e s s u b j e c ­ ted t o e l e c t r i c a l d i s c h a r g e s i n n i t r o g e n d i d n o t change dramatically. Table

III.

Mechanical P r o p e r t i e s of Parent and M o d i f i e d PET F i l m s

Sample

Modulus (Kg/cm ) 2

P a r e n t PET F i l m DMF T r e a t e d PET F i l m (140OC/15 m i n ) 8.5% pHEMA C o n t a i n ­ i n g PET F i l m

Strength ( dal\f/mm )

Extension

{%)

35,000

22

28,000

12

23.3 34.0

32,000

16

28.7

However, t h e s t a r t i n g d e c o m p o s i t i o n t e m p e r a t u r e o f f i l m s m o d i f i e d w i t h the a c r y l i c polymer decreased w i t h 60-80 C (Table I V ) , but the thermal r e s i s t a n c e remained i n p r a c ­ tical limits. c

Table

IV.

Thermal R e s i s t a n c e o f Parent and M o d i f i e d PET F i l m s

I n i t i a l Decompos i t i o n Temperature (°C)

Sample

P a r e n t PET F i l m DMF T r e a t e d PET F i l m (140°C/15 min) 8.5% pHEMA C o n t a i n ­ i n g PET F i l m

Temperature o f 5% W e i g h t L o s s (°C)

312

385

311

379

258

294

The p r e s e n c e o f t h e p o l a r h y d r o g e l on t h e s u r f a c e o f PET f i l m s l e d , a s s e e n f r o m T a b l e V, t o a d e c r e a s e i n t h e i r c o n t a c t a n g l e w i t h w a t e r and t o a c o r r e s p o n d i n g r i s e o f t h e c r i t i c a l s u r f a c e t e n s i o n t h r o u g h t h e p o l a r component fi» * ο

being

the d i s p e r s i o n

component.

S

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

17.

SIMIONESCU E T AL.

Surface Hepatization

of PET Films

Time, hrs F i g u r e 3. C o n v e r s i o n i n p o l y m e r o f HEMA i n c o r p o r a t e d i n PET f i l m s . D e p e n d e n c e on t i m e and t e m p e r a t u r e o f polymerization.

F i g u r e 4. S c a n n i n g e l e c t r o n i c m i c r o s c o p e i m a g e s U 5 C 0 0 ) o f ( a ) p a r e n t PET f i l m ; ( b ) PET f i l m t r e a t e d i n DMF a t 140°C f o r I f min; ( c ) 10.5/S pHELlA c o n t a i n i n g PET f i l m .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

236

The c o n t a c t a n g l e w i t h f o r m a m i d e r e m a i n e d a l m o s t t h e s a ­ me. As shown i n F i g u r e 5, t h e c o n t a c t a n g l e w i t h w a t e r f u r t h e r decreased i n time s i n c e the a b s o r p t i o n o f water by pHEMA i n c o r p o r a t e d i n PET i s a c c o m p a n i e d by s w e l l i n g of the h y d r o g e l , thereby i n c r e a s i n g the s u r f a c e p o l a r i t y and a b i l i t y o f t h e f i l m t o be w e t t e d . Table

V.

W e t t i n g Angle a t the Contact w i t h Water and Formamide (•%) a n d C r i t i c a l Surface Tension (t ) at 20°C s

Wetting Angle C r i t i c a l (Degree) Tension

Sample

54.0

(mU/m)

ή

w P a r e n t PET F i l m 1 0 . 5 % pHEMA C o n t a i n i n g PET F i l m

Surface

51.7

46.3

1Î

22.6

23.7

The h e p a r i n was b o n d e d t o t h e s u r f a c e o f m o d i f i e d PET f i l m s t h r o u g h t h e agency o f h y d r o x y l i c groups p r o v i d e d by t h e a c r y l i c h y d r o g e l . The p r e s e n c e o f h e p a r i n i n t h e s e f i l m s was e v i d e n c e d by g a s - c h r o m a t o g r a p h y . I t c a n be seen from F i g u r e 6 t h a t the " f i n g e r p r i n t s " of the hepar i n - r e a c t e d m o d i f i e d PET f i l m a n d h e p a r i n a r e s i m i l a r w h i l e t h e c h r o m a t o g r a m o f c o n t r o l sample i s v o i d o f p e a k s common t o t h e s e two s a m p l e s . The t h r o m b o r e s i s t a n c e o f h e p a r i n i z e d f i l m s , as shown i n T a b l e V I , was e n h a n c e d b y h i g h e r h y d r o g e l c o n t e n t s i n c e t h e c o n c e n t r a t i o n o f h y d r o x y l i c g r o u p s on mod i f i e d PET f i l m s u r f a c e , a b l e t o r e a c t w i t h g l u t a r a l d e hyde i n o r d e r t o b i n d h e p a r i n , was h i g h e r . Table

No.

1 2 3 4

PET

VI.

Thromboresistance ρHEMA C o n t a i n i n g

Sample

Control Heparinized Heparinized Heparinized

of Heparinized PET F i l m s

Incorporated pHEMA (%)

PET PET PET

8.5 2.5 6.6 8.5

C l o t t i n g Time of Blood (min) 8 22 91 108

B l o o d t h a t has been s t o r e d f o r 6 0 min i n the presence o f h e p a r i n i z e d PET f i l m s (Sample IVo. 4 ) , when p u t i n t o a n o ­ t h e r g l a s s v e s s e l was c l o t t e d w i t h i n 5 m i n , w h i c h i s t h e c l o t t i n g time o f b l o o d n o t exposed t o h e p a r i n i z e d mate­ r i a l s ( 4 ) . T h e r e f o r e , any r e d u c t i o n i n t h r o m b u s f o r m a ­ t i o n on t h e h e p a r i n i z e d f i l m s u r f a c e c a n o n l y be a t t r i ­ b u t e d t o t h e a c t i v i t y o f bound h e p a r i n , i . e . t h e f r e e h e p a r i n was n o t e l u t e d i n t o t h e b l o o d .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

17.

SIMIONESCU ET AL.

Surface Heparinization of PET Films

237

α 5

10

15 20 Time, hrs

Figure 5. The decrease of contact angle with water for / l / PET f i l m ; /2/ 8.5% pHEMA containing PET f i l m .

parent

Time (min) Figure 6. Gas chromatograms of s i l y l a t e d hydrolyzate of (a) control sample; (b) heparinized PET f i l m ; (c) heparin.

Literature Cited 1. Gott, V.L.; Whiffen, J.D.; Dutton, K.C., Science 1963, 142, 1297. 2. Leininger, R.I. In Biomedical and Dental Applications of Polymers; Gebelein, C.G.; Koblitz, F.K., Eds.; Plenum: New York, 1980. 3. Andrade, J. Hydrogels for Medical and Related Applications; American Chemical Society: Washington DC, 1976. 4. Plate, N.A.; Valuev, L.I., Biomater. 1983, 4, 14. 5. Heyman, P.W.; Kim, S.W., Makromol. Chem., Suppl. 1985,9, 119-124. 6. Gooser, M.F.A.; Sefton, M.V., J. Biomed Mater. Res. 1979, 13, 347. 7. Neeser, J.R., Carbohydr. Res. 1985, 138, 189. 8. Weigmann, H.D.; Scott, M.G.; Ribnick, A.S.; Rebenfeld, L., Text Res. J. 1976, 46, 574. 9. Avny, Y.; Rebenfeld, L.; Weigmann, H.D., J. Appl. Polymer Sci. 1978, 22, 125-147. 10. Moshnov, Α.; Avny, Y., J. Appl. Polymer Sci.1980, 25, 89. 11. Simionescu, C.I.; Denes, F.; Macoveanu, M.; Negulescu, I.I., Makromol. Chem., Suppl. 1984, 8, 17-25. R E C E I V E D August 27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 18

Reactions of Metal Vapors with Polymers 1

Colin G. Francis , Scott Lipera, Pascale D. Morand, Peter R. Morton, John Nash, and Peter P. Radford Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1062

A novel polysiloxane pendent to the backbone, has been synthesized. It is observed to react with the metal vapors of chromium, iron and nickel to afford binary metal complexes of the type M(CN-[P]) , where n = 6, 5, 4 respectively, in which the polymer-attached isocyanide group provides the stabilization for the metal center. The product obtained from the reaction with Fe was found to be photosensitive yielding the Fe (CN-[P]) species and extensive cross-linking of the polymer. The Cr and Ni products were able to be oxidized on exposure of thin films to the air, or electrochemically in the presence of an electron relay. The availability of different oxidation states for the metals in these new materials gives hope that novel redox-active polymers may be accessible. n

2

9

The p r e p a r a t i o n o f e l a b o r a t e m e t a l s p e c i e s w i t h i n polymer media r e p r e s e n t s an i m p o r t a n t s y n t h e t i c problem i n view o f the i n c r e a s i n g use o f m e t a l - c o n t a i n i n g polymers i n heterogeneous r e a c t i o n systems (1). I n t e r e s t i n these m a t e r i a l s has been prompted i n g r e a t p a r t by r e c e n t advances i n p h o t o c a t a l y s i s and e l e c t r o c a t a l y s i s , p a r t i c u l a r l y as a p p l i e d t o s o l a r energy c o n v e r s i o n p r o c e s s e s (2). Our p r e v i o u s s t u d i e s w i t h o r g a n o m e t a l l i c polymers (3) have l e d us t o i n v e s t i g a t e now the s y n t h e s i s o f new polymers which might a c t a s t e m p l a t e s f o r the f o r m a t i o n o f polymer-encapsulated binary metal complexes a t both a m o n o m e t a l l i c and c l u s t e r l e v e l . In t h i s paper, we d e s c r i b e the s y n t h e s i s and i n i t i a l r e a c t i v i t y s t u d i e s o f a macromolecule (Scheme 1) c o n t a i n i n g the i s o c y a n i d e f u n c t i o n a l group [ Z = - N r C ] t e t h e r e d t o a p o l y s i l o x a n e backbone. The polymer was designed t o i n c o r p o r a t e the f o l l o w i n g f e a t u r e s : 1

Current address: Centre Suisse d'Electronique et de Microtechnique S.A., CH-2000 Neuchatel 7, Switzerland 0097-6156/88/0364-0238$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

18.

Reactions of Metal Vapors with Polymers

FRANCIS ET AL.

239

( i ) s i m p l e s y n t h e s i s - t h e s u p p o r t i n g polymer i t s e l f i s prepared v i a a s t r a i g h t f o r w a r d one-step p o l y m e r i z a t i o n procedure (Scheme 1, s t e p 1) and can be f u l l y c h a r a c t e r i z e d b e f o r e i n c l u s i o n o f the m e t a l c e n t e r s . D i r e c t i n c o r p o r a t i o n o f m e t a l atoms by m e t a l vapor r o u t e s (4·) has been employed i n these e a r l y s t u d i e s (Scheme 1, s t e p 2) i n o r d e r t o prevent t h e f o r m a t i o n o f s i d e - p r o d u c t s whose s e p a r a t i o n would be d i f f i c u l t . ( i i ) v e r s a t i l i t y - t h e pendent i s o c y a n i d e f u n c t i o n p r o v i d e s a s i t e of attachment f o r a wide range o f t r a n s i t i o n m e t a l s (_5) and i s expected t o f a v o r f o r m a t i o n o f d i v e r s e m e t a l s t r u c t u r e s [mono- and m u l t i - m e t a l l i c ] . I t i s w o r t h w h i l e t o note t h a t the RNC m o l e c u l e i s f o r m a l l y i s o e l e c t r o n i c w i t h CO, a u b i q u i t o u s l i g a n d i n c o o r d i n a t i o n c h e m i s t r y and one well-known t o s t a b i l i z e a l a r g e number o f t r a n s ­ i t i o n m e t a l complexes ( 6 ) . 1W-:C=0

M*-:C5N-R

A

Β

S m a l l - m o l e c u l e i s o c y a n i d e s p o s s e s s a l i g a n d c h e m i s t r y which i s o n l y s l i g h t l y l e s s w e l l - d e v e l o p e d (_5). (iii) ease o f c h a r a c t e r i z a t i o n - t h e polymer, a p o l y s i l o x a n e , i s s o l u b l e i n o r g a n i c media, i n a d d i t i o n i t i s capable o f c o m p l e t i n g the c o o r d i n a t i o n sphere around each m e t a l c e n t e r , thereby f a c i l i t ­ a t i n g t h e c h a r a c t e r i z a t i o n s p e c t r o s c o p i c a l l y and s t r u c t u r a l l y , u s i n g s m a l l m o l e c u l e compounds. We s h a l l f o c u s here on t h e s y n t h e s i s o f t h e i s o c y a n i d e - c o n t a i n i n g polymer. S e v e r a l r e a c t i o n s o f t h e polymer w i t h the m e t a l v a p o r s o f Cr, Fe and N i u s i n g a m a t r i x - s c a l e modeling t e c h n i q u e , as w e l l as s y n t h e t i c - s c a l e m e t a l vapor methods, a r e then presented i n o r d e r t o demonstrate t h e r e a c t i v i t y o f t h e i s o c y a n i d e groups on t h e polymer. F i n a l l y , p r e l i m i n a r y s t u d i e s o f t h e r e a c t i v i t y o f t h e polymer-based m e t a l complexes a r e d e s c r i b e d . RESULTS AND DISCUSSION Synthesis of

Poly(dimethyl-co-isocyanopropylmethylsiloxane)

The i s o c y a n o - s u b s t i t u t e d p o l y s i l o x a n e 2_ was s y n t h e s i z e d i n h i g h y i e l d by t h e procedure shown i n Scheme 2. F o r m a t i o n o f 2_ was a c c o m p l i s h e d f o l l o w i n g known procedures (7) and c h a r a c t e r i z e d by i t s H, l^C NMR, i n f r a r e d and mass s p e c t r a . B a s e - c a t a l y z e d p o l y m e r i z ­ a t i o n o f _1 and M e S i ( O E t ) a f f o r d e d t h e branched copolymer 2. Although p o l y m e r i z a t i o n o f s i l o x a n e s i n t h e presence o f base u s u a l l y g i v e s r i s e t o low m o l e c u l a r w e i g h t s f o r t h e r e s u l t i n g polymers ( 8 ) , t h i s was the method o f c h o i c e due t o t h e a c i d - s e n s i t i v i t y o f t h e i s o c y a n i d e f u n c t i o n ( 9 ) . T y p i c a l l y , 1_ and Me2Si(0Et)2 were mixed i n an a p p r o x i m a t e l y 1:17 molar r a t i o and s t i r r e d f o r 24 h r . i n t h e presence o f a c a t a l y t i c amount o f NaOH and a d e f i c i e n c y o f water [ i . e . l e s s than 1 mole o f water p e r mole o f s i l a n e ] . Maintaining the r e a c t a n t s i n t h e dark under a n i t r o g e n atmosphere d u r i n g t h e p o l y m e r i z a t i o n l e d , a f t e r work-up, t o polymers which were c o l o r l e s s / pale-yellow viscous f l u i d s . I n most p r e p a r a t i o n s a s m a l l amount o f s o l i d polymer was a l s o o b t a i n e d . I t was p o s s i b l e t o s e p a r a t e t h i s 2

2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

18.

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Reactions of Metal Vapors with Polymers

241

s o l i d , which i s presumed t o be t h e homopolymer o f J^, by c e n t r i f u g e a t i o n . The nature o f t h e r e s u l t i n g polymer i s e x t r e m e l y s e n s i t i v e to the molar r a t i o o f water t o s i l a n e , a s shown by T a b l e I . On i n ­ c r e a s i n g t h e r a t i o f u r t h e r t o 1:1 an i n s o l u b l e rubber was o b t a i n e d . T h i s i n c r e a s e i n m o l e c u l a r weight f o l l o w s a t r e n d which has been observed p r e v i o u s l y f o r t h e h o m o p o l y m e r i z a t i o n o f M e 2 S i ( 0 E t ) 2 ( 1 0 ) . In a d d i t i o n t o m o l e c u l a r weight d e t e r m i n a t i o n s , which were c a r r i e d out by g e l permeation chromatography, 2 was c h a r a c t e r i z e d by *H and l^C NMR s p e c t r a and i t s i n f r a r e d spectrum ( F i g u r e 1 ) . The i n f r a r e d spectrum i n t h e range 2500 - 1400 cm~l shows a c h a r a c t e r i s t i c i s o ­ c y a n i d e s t r e t c h a t 2148 cm~"l. I n t h e r e g i o n o f i n t e r e s t f o r c o o r d ­ i n a t e d i s o c y a n i d e s , t h e spectrum i s c l e a r except f o r two weak bands a s s o c i a t e d w i t h t h e p o l y s i l o x a n e backbone a t 1945 and 1580 c m ~ l . The *H NMR spectrum ( F i g u r e 1) c o n t a i n s m u l t i p l e t s a t δθ.66, 1.72 and 3.34 due t o t h e p r o p y l s i d e - c h a i n , i n a d d i t i o n t o t h e resonances o f the m e t h y l groups a t δθ.08 and 0.05. The polymer c h a i n s a r e t e r m i n ­ ated by -OEt groups as e v i d e n c e d b quartet t 63.70 d triplet a t 01.18. The -^C NMR spectru as a broad s i n g l e t a t 156. c h a i n a d j a c e n t t o the CN- group o c c u r i n g a t 43.8 ppm a s t h r e e peaks of e q u a l i n t e n s i t y , due t o c o u p l i n g t o the n i t r o g e n [J^q ~ 6.1 H z ] . From the l H NMR data t h e r a t i o o f i s o c y a n i d e t o Me2Si0- groups was found t o v a r y between 1:4 and 1:13 depending on the w a t e r : s i l a n e r a t i o . As shown i n T a b l e I t h e r a t i o o f EtO- end-groups t o i s o c y a n ­ i d e f u n c t i o n s was -^2, c o n s i s t e n t w i t h a p p r o x i m a t e l y 2-3 CN- groups i n each polymer c h a i n . I n each case t h e v a l u e s o f M determined by GPC i n d i c a t e d a s l i g h t l y g r e a t e r number [3-4] o f i s o c y a n i d e groups. As w i l l be seen l a t e r , t h e e x i s t e n c e o f r e s i d u a l EtO- groups [or p o s s i b l y -OH groups] on t h e polymer 2 can l e a d t o unexpected r e a c t i o n s w i t h some m e t a l atoms. T h e r e f o r e , 2 was a l s o prepared w i t h the c h a i n - t e r m i n a t i n g groups being Me^SiO- by s t i r r i n g 2^ w i t h Me^SiOEt i n t h e presence o f base. The replacement o f t h e EtO- groups was e v i d e n c e d i n t h e N M R by t h e l o s s o f t h e resonances due t o EtO-. The procedure d e s c r i b e d here i s n o t l i m i t e d t o t h e p r e p a r a t i o n of polymers such a s 2. S t a r t i n g from the d i f u n c t i o n a l s i l a n e _3 we have s y n t h e s i z e d a copolymer, p o l y i d i m e t h y l ^ c o - i s o c y a n o p r o p y l m e t h y l s i l o x a n e ) 7_, a s w e l l a s a l i n e a r homopolymer, p o l y ( i s o c y a n o p r o p y l m e t h y l s i l o x a n e ) 8^ (Scheme 2 ) . Indeed, p r e p a r a t i o n o f a m o n o f u n c t i o n a l analogue o f 1^ and h_ c r e a t e s t h e p o t e n t i a l f o r end-capping w i t h an i s o c y a n i d e f u n c t i o n any polymer c o n t a i n i n g o t h e r f u n c t i o n a l groups, thereby i n p r i n c i p l e p e r m i t t i n g mixed l i g a n d complexes o f polymers t o be a c c e s s e d . n

M e t a l Vapor S t u d i e s w i t h 2: M e t a l atoms can be i n c o r p o r a t e d i n t o polymers u s i n g two approaches. For p r o b i n g new r e a c t i o n s between m e t a l atoms and polymers a s m a l l s c a l e s p e c t r o s c o p i c approach, sometimes r e f e r r e d t o as the F l u i d M a t r i x Technique ( 1 1 ) , i s used. The c o r e a c t a n t polymer m a t r i x , c o n t a i n i n g on t h e o r d e r o f 0.5 / i l o f polymer, i s preformed on an o p t i c a l s u r f a c e . I n the case o f v i s c o u s f l u i d s such a s 2 the mater­ i a l i s p a i n t e d on t h e s u b s t r a t e and h e l d a t t e m p e r a t u r e s r a n g i n g t y p i c a l l y from 200 t o 270 K. The temperature i s chosen t o m a i n t a i n low v o l a t i l i t y but r e t a i n m o b i l i t y . Under h i g h vacuum [10"~° t o r r ]

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

242

CHEMICAL REACTIONS ON POLYMERS

Table I. Effect of the Water-Silane Molar Ratio

a η = Weight average m o l e c u l a r weight ( M ) : Number average m o l e c u l a r weight (Mn>: Polydispersity: EtO- : -NC [Me2SiO] : -NC Number o f -NC p e r polymer c h a i n : w

b

b

0.65

0.77

0.78

1,462 1,247 1.172 2.0 4 2.5

2,463 1,719 1.433 2.2 13 2

3,123 2,468 1.265 2.0 10 2

a. moles o f water per t o t a l mole o f s i l a n e b. as determined by end-grou

WAVENUMBER 2400

NC

2200

= 2K8 cm"

2000

(cm" ) 1

1800

1600

1

JLJLJ 5

F i g u r e 1.

4 ppm

3

2

I n f r a r e d and H NMR s p e c t r a f o r CN-[P], r (It- H NMR spectrum i n C D C I 3 ; peak marked w i t h an a s t e r i s k i s due t o t h e presence o f water i n t h e s o l v e n t . ) X

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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metal atoms a r e generated r e s i s t i v e l y [0.4 /ig.min"!] and pass by a l i n e - o f - s i g h t path t o t h e s u b s t r a t e where they p e n e t r a t e and d i f f u s e i n t o t h e polymer f i l m and r e a c t w i t h f u n c t i o n a l groups p r e s e n t . P r o d u c t f o r m a t i o n can then be monitored u s i n g s p e c t r o s c o p i c t e c h ­ n i q u e s , i n t h i s case i n f r a r e d and u l t r a v i o l e t - v i s i b l e s p e c t r o s c o p y . C l e a r l y t h i s approach i s n o t s u i t a b l e f o r p r e p a r i n g l a r g e q u a n t i t i e s o f p r o d u c t s , i t s main purpose being t o p e r m i t t h e g r e a t e s t amount o f i n f o r m a t i o n t o be o b t a i n e d c o n c e r n i n g t h e r e a c t i v i t y o f a new m a t e r i a l . I f the c o r e a c t a n t i s e x p e n s i v e and/or d i f f i c u l t t o prepare then t h i s procedure i s i n v a l u a b l e . However, i t i s i m p o r t a n t to c o n s i d e r t h a t t h e q u a n t i t i e s o f d e r i v a t i z e d polymer o b t a i n e d i n t h i s approach [^10~6 mole based on -N=C r e p e a t u n i t ] might w e l l r e p ­ r e s e n t s u f f i c i e n t m a t e r i a l i f such a p r o c e s s were t o be used f o r t h e d i r e c t preparation of chemically modified electrodes (12), or i n c o r p ­ o r a t e d i n t o a p l a n a r m i c r o f a b r i c a t i o n p r o c e s s , w i t h which i t would appear t o be c o m p a t i b l e . For d e t a i l e d c h a r a c t e r i z a t i o extensiv studie i v i t y , multi-gram q u a n t i t i e vapor s y n t h e t i c r o u t e s a r t h i s i s well-documented (4) and so w i l l n o t be d e s c r i b e d i n d e t a i l here. The p r i n c i p l e s a r e those o f the F l u i d M a t r i x Technique except t h a t i n o r d e r t o accommodate 10-100 gram o f polymer, t h e c o r e a c t a n t i s c o n t a i n e d w i t h i n a r o t a t i n g f l a s k which s e r v e s t o p r o v i d e a c o n t ­ i n u o u s l y renewed f i l m as m e t a l atoms a r e produced under h i g h vacuum. F o c u s i n g on r e a c t i o n s u s i n g the F l u i d M a t r i x Technique, we have s t u d i e d t h e i n t e r a c t i o n o f chromium vapor w i t h 2 a t 200 Κ ( 1 3 ) . The r e s u l t i n g f i l m was found t o c o n t a i n m e t a l complexes e n c a p s u l a t e d w i t h i n t h e polymer i n which t h e i s o c y a n i d e group adopts a w e l l d e f i n e d o c t a h e d r a l arrangement around t h e chromium c e n t e r , i . e . a s p e c i e s o f type C r ( C N - [ P ] ) ^ . Since c h a r a c t e r i z a t i o n o f t h i s metal complex w i t h i n t h e polymer i s n o t t r i v i a l we s h a l l develop the a n a l ­ ysis i n a l i t t l e detail. The i n f r a r e d spectrum o f t h e polymer m a t r i x s p e c i e s shows a c h a r a c t e r i s t i c broad band around 1950 c m ~ l , s p l i t i n t o t h r e e peaks ( F i g u r e 2 ) . The s m a l l - m o l e c u l e model compounds Cr(CN-TESP)^ [TESP-NC = 1, Scheme 2] o r C r ( C N - B u ) a l s o show very s i m i l a r i n f r a ­ red s p e c t r a ( 1 4 ) . The IR a c t i v e s t r e t c h i n g mode f o r L i n a p u r e l y o c t a h e d r a l ML^ complex i s o f T^ symmetry. T h u s , v ç o f ° MiCO)^ [M = C r , Mo, W] appears a s a s i n g l e , sharp peak ( 1 5 ) . T h e r e f o r e , t h e s p l i t t i n g o f t h i s band i n t h e c o r r e s p o n d i n g i s o c y a n i d e complexes a r i s e s from a l o w e r i n g o f symmetry, which may be a t t r i b u t e d t o a d i s t o r t i o n o f the M(CNC-)^ fragment and a non-symmetrical o r i e n t a t i o n of t h e R groups. The o r i g i n o f t h e d i s t o r t i o n o f M(CNC-)5 can be understood by c o n s i d e r i n g t h e bonding o f [P]-NC t o the m e t a l , as shown below. E l e c t r o n d o n a t i o n from t h e i s o c y a n i d e (B) t o an e l e c t r o n - r i c h metal i s c o u n t e r b a l a n c e d by b a c k - d o n a t i o n from the m e t a l t o vacant o r b i t a l s of 7T-symmetry on t h e l i g a n d . The e f f e c t o f p o p u l a t i n g these o r b i t a l s , which a r e a n t i b o n d i n g i n n a t u r e , i s t o weaken the C-N bond so t h a t e v e n t u a l l y i n t h e l i m i t i n g case one a r r i v e s a t a s t r u c t u r e analogous t o B' i n which t h e e x t r a e l e c t r o n d e n s i t y i s l o c a l i z e d on the n i t r o g e n and the C-N-R a n g l e approaches 120°. Of course Β and B r e p r e s e n t c a n o n i c a l forms, so t h a t i n r e a l i t y a range of s t r u c t u r e s i n t e r m e d i a t e between Β and B may be r e a l i z e d . n

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2400 2000 1800 c m " ι—ι—ι—ι—ι—ι— —ι— —ι— —ι— 1

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I n f r a r e d spectrum o b t a i n e d a f t e r d e p o s i t i o n o f Cr atoms i n t o CN-[P] a t 200 Κ ( A ) . Exposure t o a i r ( B ) .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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A non-symmetrical o r i e n t a t i o n o f the R groups might be a n t i c i p a t e d f o r 2 s i n c e , w h i l e t h e p r o p y l c h a i n can be c o n s i d e r e d an antenna t o i n t r o d u c e f l e x i b i l i t y f o r c o o r d i n a t i o n , t h e r e a r e s t i l l some s t e r i c l i m i t a t i o n s t o how the polymer c h a i n ( s ) wrap around each m e t a l atom. I n t e r e s t i n g l y , the c o n t r i b u t i o n s o f these two f a c t o r s a r e r e v e a l e d when the chromium complex w i t h i n t h e polymer i s exposed t o a i r . I n the IR spectrum the band a t 1950 cm~l d i s a p p e a r s t o be r e p l a c e d by a c o m p a r a t i v e l y sharp peak a t 2085 cm~l ( F i g u r e 2) i n d i c a t i v e o f t h e f o r m a t i o n o f t h e [Cr(CN-[P]) ^ ] s p e c i e s . The sharpness o f t h i s band r e f l e c t s the h i g h e r o x i d a t i o n s t a t e o f t h e chromium l e a d i n g t o l e s s back-donation o f e l e c t r o n d e n s i t y t o t h e i s o c y a n i d e i n o t h e r words a s t r u c t u r e very c l o s e t w i t h t h e l o w symmetry i M(CNC-) d i s t o r t i o n . +

6

The C r ( C N - [ P ] ) complex can a l s o be c h a r a c t e r i z e d by i t s uvv i s i b l e spectrum ( F i g u r e 3) which c o n t a i n s a major a b s o r p t i o n band a t 298 nm w i t h a h i g h energy s h o u l d e r a t —260 nm and two l o w energy s h o u l d e r s a t —340 and —400 nm. W h i l e t h e o v e r a l l spectrum c o n s i s t s of a r a t h e r broad e n v e l o p e , a G a u s s i a n a n a l y s i s r e v e a l s t h e i n d i v i d ­ u a l peaks q u i t e c l e a r l y . W h i l e t h e C r ( C N R ) complexes f o r TESP-NC and BuNC show very s i m i l a r u v - v i s i b l e s p e c t r a ( 1 4 ) , a more u s e f u l analogy can be drawn w i t h C r ( C 0 ) ^ f o r which d e t a i l e d s p e c t r o s c o p i c a n a l y s i s e x i s t s ( 1 6 ) . A l t h o u g h symmetry f a c t o r s once a g a i n r e s u l t i n t h e spectrum o f C r ( C N - [ P ] ) ^ being broader than t h a t o f C r ( C 0 ) ^ t h e g r o s s f e a t u r e s a r e e s s e n t i a l l y t h e same. I n a s i m i l a r f a s h i o n , t h e spectrum o f C r ( C N - [ P ] ) ^ can be a s c r i b e d t o a m e t a l - t o - l i g a n d charge t r a n s f e r band [298 nm] due t o f o r m a l promotion o f an e l e c t r o n from the d - o r b i t a l s o f chromium t o the 7Γ* o r b i t a l s o f t h e i s o c y a n i d e l i g and, w i t h t h e lower i n t e n s i t y s h o u l d e r s r e s u l t i n g from l i g a n d - f i e l d t r a n s i t i o n s , i . e . r e o r g a n i z a t i o n o f t h e d - e l e c t r o n s on C r . D e p o s i t i o n o f i r o n atoms i n t o a t h i n f i l m o f 2, w i t h M = 3100 ( T a b l e I ) , r e s u l t e d i n a product w i t h an i n f r a r e d spectrum c o n s i s t i n g of bands a t 2085 and 1840 cm !. The former c o r r e s p o n d s t o an i s o ­ c y a n i d e l i g a n d p o s s e s s i n g a l i n e a r s t r u c t u r e (B) w h i l e t h e l a t t e r i s a s s o c i a t e d w i t h 'bent i s o c y a n i d e l i g a n d s ( B ) . Comparison w i t h r e s u l t s f o r s m a l l - m o l e c u l e analogues shows t h a t t h e spectrum i s c o n s i s t e n t w i t h f o r m a t i o n o f Fe(CN-[P])^ ( 1 7 ) . A f t e r u v - i r r a d i a t i o n o f the m a t r i x a t 180 Κ the t e r m i n a l r e g i o n became more complex - a new peak appeared a t 2144 cm~l w i t h a s h o u l d e r a t 2095 cm~l - and t h e band a t 1840 cm~l d i s a p p e a r e d concomitant w i t h growth o f a band a t 1660 cnT^. T h i s l a s t band i s i n d i c a t i v e o f f o r m a t i o n o f a complex i n which i s o c y a n i d e l i g a n d s b r i d g e two m e t a l c e n t e r s (_5), and we t h e r e f o r e a s s i g n the new s p e c i e s as F e 2 ( C N - [ P ] ) g . These changes i n t h e IR spectrum were accompanied by a c o l o r change o f the m a t r i x from y e l l o w t o deep orange. I n add­ i t i o n t o t h i s photochromic b e h a v i o r , t h e polymer m a t r i x , f l u i d and a i r - s e n s i t i v e before i r r a d i a t i o n , turned i n t o a s e l f - s u p p o r t i n g , a i r stable film. 0

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The same r e a c t i o n sequence was monitored by u v - v i s i b l e s p e c t r o s ­ copy and d e s p i t e the l a c k of o p t i c a l data f o r the z e r o v a l e n t b i n a r y i r o n - i s o c y a n i d e complexes, comparison w i t h the spectrum f o r Fe(CO)^ (18) r e v e a l s a c l o s e s i m i l a r i t y . A f t e r the p h o t o l y s i s the o r i g i n a l spectrum [an i n t e n s e a b s o r p t i o n a t 232 nm w i t h two s h o u l d e r s a t 297 and 340 nm] had decayed t o be r e p l a c e d by a new spectrum c o n s i s t i n g of two bands a t 220 and 382 nm. A f e a t u r e of i n t e r e s t i n t h i s system i s t h a t the d i m e r i c s p e c i e s Fe ^(0Ν-[Ρ])^ may a l s o be generated as a minor product d i r e c t l y on d e p o s i t i o n of i r o n atoms i n t o 2_ p o s s e s s i n g a lower m o l e c u l a r weight (Table I ) of M = 1500. The major d i f f e r e n c e between these two p o l y ­ mers l i e s i n the average s p a c i n g between i s o c y a n i d e groups as shown i n T a b l e I . The M e S i 0 - : -NC r a t i o i n the h i g h e r m o l e c u l a r weight polymer i s 10:1 w h i l e t h a t i n the lower m o l e c u l a r weight m a t e r i a l i s o n l y 4:1. The d i f f e r e n t r e a c t i v i t y toward i r o n atoms can then be e x p l a i n e d i n terms of the p r o b a b i l i t y of encounter between two Fei s o c y a n i d e s p e c i e s formin t different point th polyme back bone. These r e s u l t s a r I t i s a l s o importan y i e l d e d a side-product i n a d d i t i o n to Fe(CN-[P])^. T h i s s p e c i e s was c h a r a c t e r i z e d i n the i n f r a r e d spectrum by a band a t 2160 cm~l o v e r ­ l a p p i n g w i t h the f r e e l i g a n d s t r e t c h . T h i s band grew i n d e p e n d e n t l y from the o t h e r s a t the b e g i n n i n g of the d e p o s i t i o n and reached r a p i d l y a maximum a f t e r which i t s i n t e n s i t y d i d not vary w i t h i n c r ­ eased m e t a l l o a d i n g . The p o s i t i o n of the band t o h i g h e r energy r e l ­ a t i v e t o the f r e e l i g a n d s u g g e s t s a m e t a l complex c o n t a i n i n g the m e t a l i n a h i g h e r o x i d a t i o n s t a t e . Support f o r the i d e a t h a t t h i s r e s u l t s from a r e a c t i o n between an i r o n - i s o c y a n i d e s p e c i e s and t e r m i n a l Si-0H groups, which may be p r e s e n t i n s m a l l amounts i n the polymer, i s p r o v i d e d by the o b s e r v a t i o n t h a t t h i s band does not o c c u r when i r o n atoms a r e r e a c t e d w i t h the Me^SiO-capped polymer, a l t h o u g h the r e s t of the spectrum appears as normal. T u r n i n g f i n a l l y t o the r e a c t i o n of N i atoms w i t h 2, the product shows an i n f r a r e d spectrum c o n s i s t i n g of a s i n g l e s t r o n g band a t 2065 cm~l ( F i g u r e 4A). T h i s d a t a compares f a v o r a b l y w i t h t h a t f o r .the model compound Ni(CN-TESP)^ ( 1 4 ) , p e r m i t t i n g an assignment of the polymer-bound complex t o the analogous N i ( C N - [ P ] ) ^ ( 1 7 ) . I n view o f r e c e n t s t r u c t u r a l s t u d i e s w i t h N i i C N B u t ) ^ ( 1 9 ) , we can assume t h a t the p o l y m e r i c s p e c i e s c o n t a i n s a t e t r a h e d r a l arrangement of l i g a n d s around each N i atom, which i s c o n s i s t e n t w i t h o b s e r v a t i o n s from the IR spectrum. Note the r e l a t i v e l y h i g h ν^ς f o r t h i s complex, p a r t i c ­ u l a r l y when compared w i t h t h a t f o r C r ( C N - [ P ] ) ^ , which i s a cons­ equence of the l e s s f a v o r a b l e o v e r l a p between m e t a l d and l i g a n d 7Γ o r b i t a l s i n a t e t r a h e d r a l geometry. The e l e c t r o n i c spectrum of Ni(CN-[P])^ i s a l s o consistent with t h i s p i c t u r e , containing three i n t e n s e bands a t 207, 244 and 279 nm, i n good agreement w i t h the r e s u l t s f o r N i ( C N - T E S P ) and N i ( C 0 ) ( 1 4 ) . Exposure t o a i r of the m a t r i x s p e c i e s [ a t 200 K] was accompanied i n the IR spectrum by growth of a double band a t 2193/2220 cm~^ ( F i g u r e 4 B ) , w h i l e i n the e l e c t r o n i c spectrum bands appear a t 228 and 294 nm. I n o r d e r t o i n t e r p r e t these o b s e r v a t i o n s , r e s u l t s from model s t u d i e s need t o be examined. When N i ( C N B u t ) i s m u l l e d i n oxygenated N u j o l , the i n f r a r e d spectrum of the product shows two sharp bands a t 2200 and 2180 cm" and an a d d i t i o n a l peak a t 900 c m (19). This w

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U l t r a v i o l e t - v i s i b l e spectrum o f C r ( C N - [ P ] ) 5 , w i t h Gaussian r e s o l u t i o n .

Scheme 3

American Chemical Society Library 1155 16th St., N.W. In Chemical Reactions on Polymers; Washington, D.C. Benham, 20036 J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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spectrum can be a t t r i b u t e d t o a d i o x y g e n adduct NiCCNBu ) ( 0 ) ( 2 0 ) . W h i l e i t i s t e m p t i n g t o a s s o c i a t e F i g u r e 4B w i t h an analogous d i oxygen complex, the e l e c t r o n i c spectrum of the a i r - e x p o s e d polymer m a t r i x i s not c o n s i s t e n t w i t h i t s f o r m a t i o n . In a s e p a r a t e s e r i e s of e x p e r i m e n t s (21) i t was shown t h a t [ N i ( C N - [ P ] ) ^ ] [ C l O ^ ] e x h i b i t s a VNC a t 2228 cm~T". I t i s a l s o known (22) t h a t c o n p r o p o r t i o n a t i o n of t e t r a c o o r d i n a t e N i ( 0 ) and N i ( I I ) complexes of MeNC a f f o r d s a d i m e r i c complex, i . e . [Ni (CNMe)g]2+, which p o s s e s s e s a v^ç a t 2220 cm~l w i t h an e l e c t r o n i c spectrum c o n t a i n i n g a band a t 304 nm. Consi d e r a t i o n of t h e s e o b s e r v a t i o n s i n the l i g h t of our Ni/polymer s t u d i e s s u g g e s t s t h a t the i n i t i a l phase of the o x i d a t i o n i s t o the [Ni(CN-[P].] as shown i n Scheme 4. Some of the N i ( I I ) s p e c i e s then r e a c t s w i t h e x c e s s N i ( C N - [ P ] ) ^ i n the polymer m a t r i x t o g i v e the Ni (CN-[P])g]^ dimer. Independent e l e c t r o c h e m i c a l measurements (21) s u p p o r t the n y p o t h e s i s t h a t N i ( 0 ) and N i ( I I ) p r e s e n t i n the same polymer m a t r i x can r e a c t t o g i v e a d i m e r i c s p e c i e s . An i n t e r e s t i n g q u e s t i o n i vie f th demonstrated e x i s t e n c of Ni(CNBut) 2 ^ 2 ^ (20) l e a d t o an analogous s p e c i e s water i s p r e s e n t [ v i a exposure of a c o l d (200 K) s u b s t r a t e co a i r ] the o v e r a l l r e a c t i o n becomes t h a t i n which o x i d a t i o n of N i ( 0 ) t o N i ( I I ) i s accompanied by r e d u c t i o n of oxygen t o 0H~. Further studies are a n t i c i p a t e d to c l a r i f y t h i s p o i n t . The C r ( C N - [ P ] ) and N i ( C N - [ P ] ) complexes of 2 have been p r e p a r e d as w e l l under m a c r o s c a l e c o n d i t i o n s . 100 - 200 mg of m e t a l were d e p o s i t e d t y p i c a l l y i n t o a blend o f 2 i n a p o l y ( d i m e t h y l s i l o x ane) a t 270 Κ [ n o r m a l l y -10 ml of 2 i n 40 ml of d i l u e n t ] . The p r o d ­ u c t s f o r each m e t a l were dark orange, v i s c o u s o i l s which gave IR and u v - v i s i b l e s p e c t r a i n good agreement w i t h those o b t a i n e d from the matrix experiments. We have d i s c u s s e d p r e v i o u s l y t h a t the C r ( C N - [ P ] ) ^ and N i ( C N - [ P ] ) s p e c i e s can be o x i d i z e d by a i r t o the mono- and d i c a t i o n r e s p e c t i v e l y . F u r t h e r s t u d i e s w i t h the m a t e r i a l s o b t a i n e d from the m a c r o s c a l e e x p e r i m e n t s have shown t h a t o x i d a t i o n of the m e t a l c e n t e r s can be a c h i e v e d e l e c t r o c h e m i c a l l y i n the presence of an e l e c t r o n t r a n s f e r m e d i a t o r or ' r e l a y ' such as f e r r o c e n e . The experiment f o r the Cr/polymer c o m b i n a t i o n i s summarized i n F i g u r e 5, a l t h o u g h the p r i n c i p l e s a p p l y e q u a l l y f o r the N i analogue. Figure 5A shows the c y c l i c v o l t a m m e t r i c response f o r f e r r o c e n e a t a Pt e l ­ e c t r o d e - the e x p e c t e d c h e m i c a l l y and e l e c t r o c h e m i c a l l y r e v e r s i b l e c o u p l e due t o F e ( C p ) 2 / F e ( C p ) 2 . A d d i t i o n o f 2 was found t o l e a d t o an i n c r e a s e i n the peak-to-peak s e p a r a t i o n [ΔΕρ]» a t t r i b u t e d t o the i n c r e a s e d uncompensated c e l l r e s i s t a n c e or s o - c a l l e d i R drop, a l t h o u g h the c h e m i c a l r e v e r s i b i l i t y remained i n t a c t ( F i g u r e 5B). However, replacement of 2 by the d e r i v a t i z e d polymer C r ( C N - [ P ] ) ^ l e d t o a l o s s of the c h e m i c a l r e v e r s i b i l i t y , i . e . i / i l e s s than 1, a l t h o u g h t h e r e was no f u r t h e r change i n Δ Ε ( F i g u r e 5C). These o b s e r v a t i o n s f o r Fe(Cp)« i n the presence o f the polymerbound Cr complex a r e c o n s i s t e n t w i t h F e ( C p ) 2 , generated e l e c t r o ­ c h e m i c a l l y , undergoing a r e a c t i o n w i t h C r ( C N - [ P ] V r e s u l t i n g i n the c h e m i c a l r e d u c t i o n of F e ( C p ) and o x i d a t i o n of trie Cr s p e c i e s . T h e r e f o r e , when the c a t h o d i c p a r t of the Fe(Cp)2 / F e ( C p ) 2 wave i s scanned, l i t t l e f e r r i c e n i u m i o n remains t o be reduced e l e c t r o c h e m ­ ically. As a r e s u l t , the f e r r o c e n e m o l e c u l e has e f f e c t e d the t r a n s f e r of e l e c t r o n s from the polymer t o the e l e c t r o d e . 2

2

2

2 +

+

2

4

+

c

a

ρ

+

+

2

+

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2

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Reactions of Metal Vapors with Polymers

WAVENUMBER (cm" ) 2000 1800 1

2400

2200

1600

F i g u r e 4. I n f r a r e d (FTIR) spectrum o b t a i n e d a f t e r d e p o s i t i o n of N i atoms i n t o CN-[P] a t 200 Κ ( A ) . Spectrum a f t e r exposure t o a i r ( B ) .

Scheme 4

o Ni(CN-[P])

4

2

Ni(CN-[P]) J

4

2 +

Ni(CN-[p])

Ni (CN-[p]) 2

4

2 + 8

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250

CHEMICAL REACTIONS ON POLYMERS

Fc-Fc

I

Figure 5 .

0.5 VOLTS

1

C y c l i c v o l t a m m e t r i c response o f Ferrocene - ( A ) i n C H 2 C I 2 , (B) w i t h added CN-[P], (C) a f t e r a d d i t i o n of C r ( C N - [ P ] ) . 6

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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Reactions of Metal Vapors with Polymers

FRANCIS ET AL.

251

We can see t h a t f e r r o c e n e i s i d e a l l y s u i t e d t o t h i s a p p l i c a t i o n from model compounds. Using C r ( C N B u ) 6 as our model f o r the polymerbased Cr complex ( 2 1 ) , we can e s t i m a t e t h a t the K q f o r r e a c t i o n between f e r r i c e n i u m and C r f C N - [ P ] ) 6 , l e a d i n g t o removal of one e l e c t r o n , i s approximately 1 0 ^ . I t i s a l s o thermodynamically f a v o r a b l e [ K ^ 1 0 ] f o r a second e l e c t r o n t o be removed t o g i v e the bound Cr(II) species. I n n e i t h e r case - C r ( C N - [ P ] ) 5 or N i ( C N - [ P ] ) 4 - was a c y c l i c v o l t a m m e t r i c response observed d i r e c t l y f o r the m e t a l c e n t e r a t a P t e l e c t r o d e , f o r e i t h e r s o l u t i o n phase or s u r f a c e - c o n f i n e d m a t e r i a l s . The s o l u t i o n phase b e h a v i o r i n t h i s r e s p e c t i s very s i m i l a r t o the s i t u a t i o n encountered w i t h many b i o l o g i c a l macromolecules ( 2 3 ) . S i n c e model compounds r e v e a l w e l l - d e f i n e d c y c l i c voltammograms f o r the Cr(CNR)5 Ni(CNR)5 complexes (21) the o r i g i n o f the e l e c t r o i n a c t i v i t y of the polymers i s not o b v i o u s . A possible explanation (12) i s t h a t the ohmic r e s i s t a n c e a c r o s s the i n t e r f a c e between the e l e c t r o d e and polymer, du t th absenc f i o n w i t h i th polymer r e n d e r s the p o t e n t i a l l y assuming the absence of important t o c o n s i d e r t h a t the n a t u r e of the e l e c t r o d e s u r f a c e may i n f l u e n c e the type of polymer f i l m o b t a i n e d . A r e c e n t o b s e r v a t i o n which bears on these p o i n t s i s t h a t when one s t a r t s w i t h the chromium polymer i n the [Cr(CN-[P])fr]2+ s t a t e , an e l e c t r o a c t i v e polymer f i l m may be o b t a i n e d on a g l a s s y carbon e l e c t r o d e . T h i s w i l l c o n s t i t u t e the s u b j e c t o f a f u t u r e paper. n

e

1 2

e q

a n d

EXPERIMENTAL NMR s p e c t r a were recorded on a JEOL FX90Q (90 MHz) s p e c t r o m e t e r . ^-H c h e m i c a l s h i f t s a r e r e p o r t e d r e l a t i v e t o an i n t e r n a l s t a n d a r d of CHCI3 i n C D C I 3 , w h i l e l ^ C c h e m i c a l s h i f t s are r e p o r t e d r e l a t i v e t o the CDCI3 used as s o l v e n t . I n f r a r e d s p e c t r a were recorded on an IBM IR32 FTIR o r a P e r k i n - E l m e r 1330 IR s p e c t r o p h o t o m e t e r . U v - v i s i b l e s p e c t r a were o b t a i n e d u s i n g a V a r i a n DMS90 s p e c t r o p h o t o m e t e r . M o l e c u l a r w e i g h t s were measured by g e l permeation chromatography on a P e r k i n - E l m e r S e r i e s 10 L i q u i d Chromatograph u s i n g t e t r a h y d r o f u r a n as s o l v e n t and r e f r a c t i v e index as the d e t e c t i o n mode. S t a n d ards were p o l y s t y r e n e , and r e p o r t e d m o l e c u l a r w e i g h t s f o r the p o l y s i l o x a n e s do not i n c l u d e a c o r r e c t i o n . T r i e t h o x y s i l a p r o p y l a m i n e was purchased from P e t r a r c h Systems. D i m e t h y l d i e t h o x y s i l a n e and m e t h y l t r i e t h o x y s i l a n e were purchased from Aldrich. S y n t h e s i s of 2: The t r i e t h o x y s i l a p r o p y l i s o c y a n i d e _1 was prepared as o u t l i n e d i n r e f erence 7, and c h a r a c t e r i z e d by i t s ! H , 13C NMR, IR and mass s p e c t r a . For d e t a i l s see r e f e r e n c e 14. Aqueous NaOH [0.09 g i n 3 ml H2O] was added dropwise t o a m i x t u r e of 30 ml [0.17 mole] of (Et0)2SiMe2 and 2.5 ml [0.01 mole] of ( E t 0 ) S i ( C H ) 3 N C . The s o l u t i o n was s t i r r e d under an i n e r t atmosphere f o r 24 h r . i n the dark a t room temperature. A f t e r c o m p l e t i o n of the r e a c t i o n , the r e s i d u e was washed t h o r o u g h l y w i t h water u n t i l n e u t r a l . I t was then resuspended i n hexane and d r i e d over MgS04 ^ s e v e r a l hours. The s o l u t i o n was decanted, the 3

2

o r

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CHEMICAL REACTIONS ON POLYMERS

s o l v e n t removed i n vacuo and the polymer p u r i f i e d by s u b l i m a t i o n , affording a c l e a r , viscous l i q u i d . In t h e case where end-capping of the c h a i n s was n e c e s s a r y , t h i s was a c h i e v e d by s t i r r i n g 2 w i t h a f i v e - f o l d e x c e s s of (EtO)3SiMe i n aqueous base f o r 24 h r . The r e s u l t i n g polymer was worked-up as before. 2 - l H nmr ( C D C I 3 ) : 03.70 ( q , CH3CH2O), 3.34 ( t , C H 2 N C ) , 1.72 (m, CH2CH?NC), 1.18 ( t , CH3CH2O), 0.66 (m, C ^ S i ) , 0.08, 0.05 ( C H 3 S 1 ) . Î 3

C

nmr

(CDCI3):

156.0

(NC),

(CH3CH2O),

57.6

43.8

(t, J

N

C

=

6.1

Hz, CH NC), 23.5 (CH CH NC), 18.2 ( C H C H 0 ) , 10.8, 9.7, 8.6 ( C H S i ) , 0.89, -1.17 ( C H S i 7 /ppm IR ( n e a t ) : 2965s, 2905m, 2148s (vNC>. 1392m, 1261vs, 1090vs, 954s, 802vs cm"!. 2

2

2

3

2

2

3

M e t a l Vapor Polymer M a t r i x D e p o s i t i o n s : The m e t a l vapors were generated b r e s i s t i v h e a t i n f metal f i l aments [Fe, N i ] o r Knudse The polymer m a t r i x was prepare o p t i c a l support [ q u a r t z f o r u v - v i s i b l e ; N a C l , KBr or C s l f o r IR monitoring]. The m a t r i x was a l l o w e d t o degas t h o r o u g h l y under vacuum and was then m a i n t a i n e d a t 200 Κ under dynamic vacuum [10-6-10-7 torr]. The metal vapor was d e p o s i t e d i n t o the c o l d f i l m a t d e p o s i t ­ i o n r a t e s on the o r d e r of 0.4 | i g . m i n - l . The ensuing r e a c t i o n s were monitored by u v - v i s i b l e and i n f r a r e d s p e c t r o s c o p y . M a c r o s c a l e M e t a l Vapor R e a c t i o n s : I n a t y p i c a l r e a c t i o n 100 - 200 mg of m e t a l [Cr o r N i ] was evaporated from a preformed a l u m i n a c r u c i b l e over a p e r i o d o f 60 - 90 min and d e p o s i t e d i n t o a m i x t u r e of 2 i n p o l y ( d i m e t h y l s i l o x a n e ) [ P e t r a r c h Systems; 0.1 P.] w i t h i n a r o t a r y s o l u t i o n m e t a l vapor r e a c t o r o p e r ­ a t i n g a t 10~4 t o r r . The r e a c t i o n f l a s k was c o o l e d t o a p p r o x i m a t e l y 270 Κ by an i c e d - w a t e r b a t h . For a d e s c r i p t i o n o f the apparatus see Chapter 3 o f r e f e r e n c e 4. The product i n each case was a dark orange v i s c o u s l i q u i d and was c h a r a c t e r i z e d as o b t a i n e d from the r e a c t i o n vessel. E l e c t r o c h e m i c a l Measurements: A l l e l e c t r o c h e m i c a l measurements were performed employing a t h r e e e l e c t r o d e arrangement w i t h P t o r g l a s s y c a r b o n working and a u x i l i a r y e l e c t r o d e s and a Ag w i r e p s e u d o - r e f e r e n c e e l e c t r o d e s e p a r a t e d from the b u l k s o l u t i o n by a V i c o r membrane. The wave g e n e r a t o r / p o t e n t i o s t a t was a BAS I n s t r u m e n t s Model CV-1B connected t o a Houston I n s t r ­ uments 2000 r e c o r d e r . A l l m a t e r i a l s were l o a d e d i n t o the c e l l under a n a e r o b i c c o n d i t i o n s and d r i e d , degassed s o l v e n t s [ C H C 1 , CH3CN, t h f ] and degassed s u p p o r t i n g e l e c t r o l y t e [ t e t r a - b u t y l a m m o n i u m - h e x a f l u o r o p h o s p h a t e ] were used. I n g e n e r a l , p o t e n t i a l s a r e r e p o r t e d r e l a t i v e t o f e r r o c e n e as i n t e r n a l s t a n d a r d . 2

2

n

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ACKNOWLEDGMENTS We w i s h t o thank the 3M Company f o r f i n a n c i a l s u p p o r t o f t h i s r e s e a r c h and the V a n t H o f f Fund f o r the purchase o f the e l e c t r o c h e m i c a l equipment. PPR acknowledges the U n i v e r s i t y o f Southern C a l i f o r n i a f o r the award o f a Moulton F e l l o w s h i p . T

LITERATURE CITED 1. Kaneko, M.; Yamada, A. Adv. Polymer Sci. 1984, 55, 2. 2. Grätzel, M. Energy Resources through Photochemistry and Catalisis; Academic Press: New York, 1983. 3. Francis, C.G.; Morand, P.D.; Spare, N.J. Organometallics 1985, 4, 1958. [and references therein] 4. Moskovits, M.; Ozin, G.A. Cryochemistry; Wiley: New York, 1976. 5. Singleton, E.; Oosthuizen, H.E. Adv. Organometal. Chem. 1983, 22, 209. 6. Cotton, F.A.; Wilkinson New York, 1980, pp 7. Howell, J.A.S.; Berry, M. J. Chem. Soc., Chem. Commun. 1980, 1039. 8. Eaborn, C. Organosilicon Compounds; Academic Press: London, 1960. 9. Ugi, I. Isonitrile Chemistry; Academic Press: New York, 1971. 10. Fletcher, H.J.; Hunter, M.J. J. Am. Chem. Soc. 1949, 71, 2918. 11. Francis, C.G., Ozin, G.A. J. Macromol. Sci.-Chem. 1981, A16, 167. 12. Murray, R.W. In Electroanalytical Chemistry; Bard, A.J., Ed.; Marcel Dekker: New York, 1983; Vol. 13. 13. Francis, C.G.; Klein, D.; Morand, P.D. J. Chem. Soc., Chem. Commun. 1985, 1142. 14. Morand, P.D. Ph.D. Thesis, Univ. Southern California, 1986. 15. Amster, R.L.; Hannan, R.B.; Tobin, M.C. Spectrochim. Acta 1963, 19, 1489. [and references therein] 16. Beach, N.A.; Gray, H.B. J. Am. Chem. Soc. 1968, 90, 5713. 17. Francis, C.G.; Morand, P.D.; Radford, P.P. J. Chem. Soc., Chem. Commun. 1986, 211. 18. Dartiguenave, M.; Dartiguenave, Y.; Gray, H.B. Bull. Soc. Chim. France 1969, 4223. 19. Morton, P.R. Ph.D. Thesis, Univ. Southern California, 1987. 20. Otsuka, S.; Nakamura, Α.; Tatsuno, Y. J. Am. Chem. Soc. 1969, 91, 6994. 21. Radford, P.P. Ph.D. Thesis, Univ. Southern California, 1987. 22. DeLaet, D.L.; Powell, D.R.; Kubiak, C.P. Organometallics 1985, 4, 954. 23. Margoliash, E.; Schejter, A. In Advances in Protein Chemistry; Anfinsen, C.B.; Anson, M.L.; Edsall, J.T.; Richards, F.M., Eds.; Academic Press: New York, 1966; Vol. 21. RECEIVED August

27, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 19

Synthesis and Characterization of Block Copolymers Containing Acid and Ionomeric Functionalities 1

2

T. E. Long , R. D. Allen , and J . E. McGrath

3

Department of Chemistry and Polymer Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, V A 24061-0699

By employing anioni containing block copolyme with controlled compositions, predictable molecular weights and narrow molecular weight distributions. Subsequent hydrolysis of the ester functionality to the metal carboxylate or carboxylic acid can be achieved either by potassium superoxide or the acid catalyzed hydrolysis of t-butyl methacrylate blocks. The presence of acid and ion groups has a profound effect on the solution and bulk mechanical behavior of the derived systems. The synthesis and characterization of various substituted styrene and all-acrylic block copolymer precursors with alkyl methacrylates will be discussed. In addition, the polymer modification reactions leading to acidic and ionomeric functionalities are described in detail. The derived ion-containing block copolymers may aid in the correlation of chemical architecture with ionomer morphology and properties. The n e c e s s i t y o f n o v e l p o l y m e r i c systems f o r s p e c i f i c e l e c t r o a c t i v e a p p l i c a t i o n s has m o t i v a t e d s i g n i f i c a n t r e s e a r c h e f f o r t s i n polymer s y n t h e s i s and c h a r a c t e r i z a t i o n ( 1 - 4 ) . In a d d i t i o n t o the preparation of c o n d u c t i n g , charge t r a n s f e r , and n o n - l i n e a r o p t i c p o l y m e r i c m a t e r i a l s , an abundance of i n d u s t r i a l and academic a t t e n t i o n has been d e v o t e d t o t h e i n t r o d u c t i o n of i o n s t o a h y d r o c a r b o n backbone (5-7 ). The i n t e r e s t i n ionomers has been encouraged by t h e r e a l i z a t i o n t h a t s m a l l amounts of i o n s (10 mole p e r c e n t o r l e s s ) can d r a s t i c a l l y m o d i f y polymer p r o p e r t i e s . However, a d e t a i l e d u n d e r s t a n d i n g o f t h e o r i g i n of ionomer p r o p e r t i e s has been d i f f i c u l t t o a c h i e v e . This i s presumably due t o t h e complex aggregate morphology t h a t r e s u l t s from

1

Current address: Eastman Kodak Company, 1999 Lake Avenue, Rochester, N Y 14650

2

Current address: IBM Almaden Research Center, 650 Harry Road, San Jose, CA

95120-6099

Correspondence should be addressed to this author. 0097-6156/88/0364-0258$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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259

electrostatic interactions. In most i n v e s t i g a t i o n s , t h e r o l e of polymer a r c h i t e c t u r e has not been a d d r e s s e d and i t i s b e l i e v e d t h a t t h i s v a r i a b l e w i l l have a p r o f o u n d i n f l u e n c e on the development of t h e morphology. F o r i n s t a n c e , the c o n t r o l l e d placement of an i o n i c f u n c t i o n a l i t y i n b l o c k - l i k e sequences v e r s u s random i n c o r p o r a t i o n may s i g n i f i c a n t l y a l t e r the e x t e n t and mechanisms of coulombic interaction. S e v e r a l complimentary t e c h n i q u e s have been d e v e l o p e d i n our l a b o r a t o r i e s which a l l o w f o r the s y n t h e s i s of charged polymers with c o n t r o l l e d a r c h i t e c t u r e . The s y n t h e t i c c a p a b i l i t i e s d e s c r i b e d h e r e i n w i l l f a c i l i t a t e the c o r r e l a t i o n of ionomer s t r u c t u r e w i t h v a r i o u s t h e r m a l , m e c h a n i c a l , r h e o l o g i c a l , and s c a t t e r i n g p r o p e r t i e s . A l t h o u g h the f o c u s of t h i s work i s on the s y n t h e s i s of model i o n c o n t a i n i n g b l o c k copolymers, the copolymer p r e c u r s o r s may a l s o demonstrate p o t e n t i a l u t i l i t y . C a r b o x y l i c a c i d c o n t a i n i n g polymers have been c o n v e n t i o n a l l y p r e p a r e d by the d i r e c t f r e e r a d i c a l p o l y m e r i z a t i o n of a c r y l i c or m e t h a c r y l i c a c i d w i t h v a r i o u v i n y l (8,9). The c o r r e s p o n d i n o b t a i n e d by p a r t i a l l y o groups w i t h a v a r i e t y of b a s e s . The s e l e c t i o n of the base d i c t a t e s the v a l e n c y of the c o u n t e r i o n and has been shown t o be i m p o r t a n t i n the d e t e r m i n a t i o n of r h e o l o g i c a l and m e c h a n i c a l p r o p e r t i e s (10,11). These s y n t h e t i c r o u t e s r e s u l t i n the random placement of i o n i c groups a l o n g polymer backbones. The heterogeneous c o m p o s i t i o n of these m a t e r i a l s has made c h a r a c t e r i z a t i o n and i n t e r p r e t a t i o n of s t r u c t u r e - p r o p e r t y correlation quite d i f f i c u l t . A n i o n i c t e c h n i q u e s , i n f a v o r a b l e c a s e s , e n a b l e one t o s y n t h e s i z e b l o c k copolymers w i t h c o n t r o l l e d c o m p o s i t i o n and a r c h i t e c t u r e , p r e d i c t a b l e m o l e c u l a r w e i g h t s , and narrow m o l e c u l a r weight d i s t r i b u t i o n s . In p a r t i c u l a r , we have devoted s i g n i f i c a n t a t t e n t i o n t o t h e s y n t h e s i s of a c r y l i c - a c r y l i c and s t y r e n i c - a c r y l i c b l o c k copolymers ( 1 2 ) . P r e s e n t r e s e a r c h e f f o r t s a r e f o c u s e d on t h e s y n t h e s i s of d i e n e - a c r y l i c b l o c k copolymers and hydrogenated d e r i v a t i v e s (13^). The d i e l e c t r i c c o n s t a n t of the f i r s t b l o c k may p l a y a s i g n i f i c a n t r o l e i n d e t e r m i n i n g t h e f i n a l a g g r e g a t e morphology. One can s y s t e m a t i c a l l y v a r y the p o l a r i t y of the f i r s t b l o c k from t h e v e r y n o n p o l a r d i e n e phase t o t h e m o d e r a t e l y p o l a r a l k y l methacrylate. The i n t r o d u c t i o n of i o n o m e r i c f u n c t i o n a l i t i e s can be a c c o m p l i s h e d i n a c o n t r o l l e d f a s h i o n by t h e subsequent h y d r o l y s i s of the p o l y m e r i c e s t e r f u n c t i o n a l i t y o f v a r i o u s a l k y l methacrylates. Our e a r l i e r i n v e s t i g a t i o n s have i n t r o d u c e d the use of p o t a s s i u m s u p e r o x i d e ( 0 ) h y d r o l y s i s of a wide range of p o l y ( a l k y l m e t h a c r y l a t e s ) ( 1 4 ) . R e c e n t l y , we have d e v e l o p e d the p r o p e r t e c h n i q u e s f o r the i n t r o d u c t i o n of t - b u t y l m e t h a c r y l a t e (TBMA) i n t o b l o c k copolymer systems. I t i s w e l l - e s t a b l i s h e d t h a t the h y d r o l y s i s of e s t e r s c o n t a i n i n g a l k y l groups which can s t a b i l i z e carbenium i o n s , e.g. t - b u t y l , undergo m i l d a c i d c a t a l y z e d a l k y l oxygen cleavage ( ^ ) (.15)· I n a d d i t i o n t o t h e a b i l i t y t o form s t a b l e carbenium i o n s , t h e p r e s e n c e o f 3~hydrogen i n the e s t e r a l k y l group p r o v i d e s f o r a mechanism o f e l i m i n a t i o n , e.g. R

f

o

r

t

h

e

2

A

A L

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

260

CHEMICAL REACTIONS ON POLYMERS

i s o b u t y l e n e f o r TBMA h y d r o l y s i s . T h i s a t t r i b u t e d r i v e s the r e a c t i o n t o v e r y h i g h c o n v e r s i o n s (>95%). We have r e p e a t e d l y employed t h i s second h y d r o l y s i s approach f o r the s y n t h e s i s of t a c t i c p o l y ( m e t h a c r y l i c a c i d ) , e.g. 100% isotactic poly(methacrylic acid). Due t o the l i m i t e d c o n v e r s i o n (60-70%) of t h e KC>2 r o u t e , the c a r b o x y l a t e b l o c k would c o n t a i n u n r e a c t e d e s t e r f u n c t i o n a l i t y . On the o t h e r hand, a b l o c k c o m p r i s e d s o l e l y o f m e t a l c a r b o x y l a t e can be p r e p a r e d by the a c i d catalyzed hydrolysis. I t i s w e l l known t h a t i n t e r - and i n t r a m o l e c u l a r forces p l a y a v e r y i m p o r t a n t r o l e i n d e t e r m i n i n g polymer m o r p h o l o g i e s and p r o p e r t i e s . F o r the c a s e of a c i d c o n t a i n i n g p o l y m e r s , i t has been r e p o r t e d t h a t the o c c u r r e n c e of hydrogen bonding d r a s t i c a l l y a f f e c t s such p r o p e r t i e s as the g l a s s t r a n s i t i o n t e m p e r a t u r e (16,17). I n a d d i t i o n , m e c h a n i c a l and d i e l e c t r i c r e l a x a t i o n s may s h i f t w i t h i n c r e a s i n g a c i d c o n t e n t . In a s i m i l a r f a s h i o n , polyme propertie drasticall chang w i t h th i n c o r p o r a t i o n of i o n i c g r o u p of these m o i e t i e s (8,18) scheme i n v o l v i n g two t y p e s of a g g r e g a t e s . Multiplets consist o f s m a l l groups of i o n p a i r s w i t h no p o l y m e r i c c o n t e n t which s e r v e as s i m p l e m u l t i f u n c t i o n a l c r o s s l i n k p o i n t s . Clusters a r i s e from f u r t h e r a g g r e g a t i o n of m u l t i p l e t s t o form a l a r g e r , more l o o s e l y a s s o c i a t e d , s t r u c t u r e which may have a p p r e c i a b l e h y d r o c a r b o n (polymer) c o n t e n t . C l u s t e r s a r e t h u s analogous t o a m i c r o p h a s e s e p a r a t e d " h a r d segmented" i n a c o n v e n t i o n a l b l o c k o r segmented copolymer. A d i s c u s s i o n of t h e v a r i o u s m o l e c u l a r parameters a f f e c t i n g c l u s t e r f o r m a t i o n i n ionomers e n a b l e s one to b e t t e r understand the d r i v i n g forces f o r aggregation. Thus, one can c o n t r o l the morphology and p h y s i c a l p r o p e r t i e s of t h e s e systems. The m o l e c u l a r p a r a m e t e r s a f f e c t i n g a g g r e g a t i o n i n ionomers include: ion content, i o n type, counterion, percent n e u t r a l i z a t i o n , backbone d i e l e c t r i c c o n s t a n t and r e l a t i v e p o s i t i o n o f i o n i c groups i n a polymer c h a i n . The f i r s t f i v e f a c t o r s a r e e a s i l y c o n t r o l l e d and have been shown t o a f f e c t the morphology and p h y s i c a l p r o p e r t i e s of i o n o m e r s . Less a t t e n t i o n has been f o c u s e d on i o n placement due p r i m a r i l y t o the synthetic d i f f i c u l t i e s involved. Preliminary investigations i n d i c a t e t h a t t h i s f a c t o r may e x e r t a s t r o n g i n f l u e n c e on ionomer p r o p e r t i e s . A n i o n i c techniques i n combination with v a r i o u s subsequent polymer m o d i f i c a t i o n r e a c t i o n s y i e l d a wide range of i o n - c o n t a i n i n g m a t e r i a l s and p r o v i d e e x t e n s i v e i n s i g h t i n t o t h e i r unique p r o p e r t i e s . Experimental Materials. S t y r e n e ( A l d r i c h ) and t - b u t y l s t y r e n e (Dow C h e m i c a l ) were p u r i f i e d by d i s t i l l a t i o n from d i b u t y l magnesium (DBM). T h i s r e a g e n t has been shown by F e t t e r s e t a l . (19) t o s u c c e s s f u l l y remove water and a i r from v a r i o u s h y d r o c a r b o n monomers. In some c a s e s , the s t y r e n i c monomers can be p a s s e d t h r o u g h columns of s i l i c a and a c t i v a t e d a l u m i n a f o l l o w e d by d e g a s s i n g t o o b t a i n a n i o n i c grade monomers.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

19.

L O N G ET AL.

Synthesis and Characterization of Block Copolymers

D i p h e n y l e t h y l e n e (DPE) was o b t a i n e d from Eastman Kodak Co. and was p u r i f i e d by vacuum d i s t i l l a t i o n from s_-butyl l i t h i u m . The y e l l o w i s h c o l o r a s s o c i a t e d w i t h the crude DPE d i s a p p e a r s after purification. The a l k y l m e t h a c r y l a t e monomers were a v a i l a b l e from various sources. I s o b u t y l m e t h a c r y l a t e (IBMA) (Rohm and Haas) and t - b u t y l m e t h a c r y l a t e (TBMA) (Rohm Tech) may be p u r i f i e d f i r s t by d i s t i l l a t i o n from C a H , f o l l o w e d by d i s t i l l a t i o n from t r i a l k y l aluminum r e a g e n t s as d e s c r i b e d i n d e t a i l e a r l i e r (20,21). I n p a r t i c u l a r , t - b u t y l m e t h a c r y l a t e ( b . p t . ~150°C) was s u c c e s s f u l l y p u r i f i e d by d i s t i l l a t i o n , from t r i e t h y l aluminum c o n t a i n i n g s m a l l amounts of d i i s o b u t y l aluminum hydride. The t r i a l k y l aluminum and d i a l k y l aluminum h y d r i d e r e a g e n t s were o b t a i n e d from the E t h y l C o r p o r a t i o n as 25 weight p e r c e n t s o l u t i o n s i n hexane. The i n i t i a t o r , s - b u t y l l i t h i u m , was o b t a i n e d from the L i t h c o D i v i s i o n of FMC, and a n a l y z e d by the Gilman "double t i t r a t i o n " ( 2 2 ) . Most p o l y m e r i z a t i o n (THF) ( F i s h e r , C e r t i f i e d i s t i l l e d from the p u r p l e sodium/benzophenone k e t y l . 9

Polymerization. A l l g l a s s w a r e was r i g o r o u s l y c l e a n e d and d r i e d i m m e d i a t e l y p r i o r t o use. F o r s m a l l s c a l e p o l y m e r i z a t i o n s , the r e a c t o r c o n s i s t e d of a 250 mL, 1 neck, round bottom f l a s k e q u i p p e d w i t h a magnetic s t i r r e r and a r u b b e r septum. The septum was s e c u r e d i n p l a c e w i t h copper w i r e i n o r d e r t h a t a p o s i t i v e p r e s s u r e o f p r e p u r i f i e d n i t r o g e n c o u l d be m a i n t a i n e d . The r e a c t o r was assembled w h i l e hot and s u b s e q u e n t l y flamed under a n i t r o g e n purge. A f t e r the f l a s k had c o o l e d , the p o l y m e r i z a t i o n s o l v e n t was added t o the r e a c t o r v i a a d o u b l e ended n e e d l e . The r e a c t o r was submerged i n t o a -78°C b a t h and a l l o w e d t o r e a c h thermal e q u i l i b r i u m . P u r i f i e d s t y r e n e monomer was charged i n t o the r e a c t o r w i t h a s y r i n g e . The c a l c u l a t e d charge of i n i t i a t o r was q u i c k l y s y r i n g e d i n t o the r e a c t o r and i m m e d i a t e l y one c o u l d see t h e f o r m a t i o n of the orange s t y r y l anion. The f i r s t b l o c k was a l l o w e d t o p o l y m e r i z e f o r o v e r 20 m i n u t e s t o ensure complete c o n v e r s i o n . A s l i g h t excess of DPE (2-3 molar e x c e s s compared t o l i t h i u m ) was s y r i n g e d i n t o the r e a c t o r i n o r d e r t o cap t h e f r o n t b l o c k . T h i s capping p r o c e d u r e was e s s e n t i a l i n most cases t o p r e v e n t c a r b o n y l a t t a c k (1,2 a d d i t i o n ) of t h e a l k y l m e t h a c r y l a t e monomer. The s u c c e s s f u l c o n v e r s i o n of the h i g h l y d e l o c a l i z e d d i p h e n y l e t h y l e n e d e r i v e d a n i o n was w i t n e s s e d by the r a p i d f o r m a t i o n of a deep r e d c o l o r . A f t e r s e v e r a l minutes, h i g h l y p u r i f i e d a l k y l m e t h a c r y l a t e monomer was s l o w l y added t o the l i v i n g capped f i r s t block. I n i t i a t i o n of t h e second b l o c k was r a p i d and was c h a r a c t e r i z e d by t h e f o r m a t i o n of a c o l o r l e s s p o l y ( a l k y l methacrylate) enolate anion. A f t e r 15-20 m i n u t e s , the p o l y m e r i z a t i o n c o u l d be t e r m i n a t e d by t h e a d d i t i o n of a few drops of degassed methanol. The polymer can f i n a l l y be o b t a i n e d by p r e c i p i t a t i n g i n a l a r g e excess (10X) o f n o n s o l v e n t such as methanol o r m e t h a n o l / i s o p r o p a n o l depending on the s o l u b i l i t y c h a r a c t e r i s t i c s of the polymer.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

Hydrolysis. Two methods of h y d r o l y s i s have been employed, tB u t y l m e t h a c r y l a t e homopolymers and b l o c k copolymers were e a s i l y h y d r o l y z e d u s i n g c a t a l y t i c amounts of £-toluene s u l f o n i c a c i d monohydrate (PTSA) i n s o l u t i o n a t m i l d temperatures (6080°C). Other a c i d c a t a l y s t s have a l s o been s t u d i e d . The c h o i c e o f s o l v e n t was c r i t i c a l s i n c e m a i n t a i n i n g solubility l e a d s t o h i g h e r degrees of h y d r o l y s i s . T o l u e n e ( F i s h e r , C e r t i f i e d Grade) i s an e x c e l l e n t s o l v e n t f o r the b l o c k copolymers s i n c e the amount of i n c o r p o r a t e d t - b u t y l m e t h a c r y l a t e was g e n e r a l l y l e s s than 10% by w e i g h t . For homopolymers, the a d d i t i o n of methanol w i l l m a i n t a i n s o l u b i l i t y t h r o u g h o u t the r e a c t i o n . Although t h i s technique i s f a c i l e , i t i s o n l y a p p l i c a b l e t o c e r t a i n e s t e r s as d e s c r i b e d i n the introduction. Scheme I d e p i c t s the h y d r o l y s i s of p o l y ( t - b u t y l styrene)-b-poly(t-butyl methacrylate). C o n v e r s i o n t o the m e t a l c a r b o x y l a t e i s a c c o m p l i s h e d by simple t i t r a t i o n of the a c i d groups w i t h an a p p r o p r i a t e base e.g KOH (Normal/10 i n methanol), using phenolphthalei techniques f o r superoxid d e t a i l e a r l i e r (14). Scheme I . Hydrolysis

of P o l y ( t - B u t y l M e t h a c r y l a t e ) C o n t a i n i n g Copolymers CH.

Block

3

+

Toluene, H 80°C 8 Hrs.

CH

C(CH ) 3

Characterization. M o l e c u l a r weight and d i s t r i b u t i o n s of the d i b l o c k p r e c u r s o r s

3

3

I

m o l e c u l a r weight and a c i d c o n t a i n i n g

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

19. L O N G E T A L .

Synthesis and Characterization of Block Copolymers

polymers were determined p r i m a r i l y by s i z e e x c l u s i o n chromatography (SEC). A v a r i a b l e temperature Waters |90 GPC equipped w i t h u l t r a s t y r a g e l columns of 500Â, 10 Â, 10 Â and 10 Â was employed. A Waters 490 programmable wavelength d e t e c t o r and a Waters R401 d i f f e r e n t i a l r e f r a c t i v e index d e t e c t o r were u t i l i z e d . Both PMMA and PS s t a n d a r d s (Polymer L a b o r a t o r i e s ) were used f o r the c o n s t r u c t i o n of c a l i b r a t i o n curves. F o u r i e r t r a n s f o r m i n f r a r e d (FTIR) s p e c t r o s c o p y was p e r f o r m e d on a N i c o l e t 10DX s p e c t r o m e t e r . N u c l e a r magnetic resonance ( H) c h a r a c t e r i z a t i o n was a c c o m p l i s h e d u s i n g an IBM 270 SL. Both t e c h n i q u e s can s u c c e s s f u l l y be u t i l i z e d t o a n a l y z e b o t h the d i b l o c k p r e c u r s o r s as w e l l as the d e r i v e d a c i d c o n t a i n i n g polymers. Thermal a n a l y s i s (DSC, TMA, TGA) was p e r f o r m e d w i t h e i t h e r a P e r k i n - E l m e r Model 2 o r Model 4. R e s u l t s and D i s c u s s i o n A v e r y c r i t i c a l , but not always a p p r e c i a t e d , a s p e c t of b l o c k copolymer s y n t h e s i s by l i v i n g p o l y m e r i z a t i o n t e c h n i q u e s i s monomer p u r i t y . T h i s c o n s i d e r a t i o n i s p a r t i c u l a r l y important when h i g h m o l e c u l a r w e i g h t polymers (>5.0xl0 g/mole) are d e s i r e d , and the c o r r e s p o n d i n g a n i o n c o n c e n t r a t i o n i s q u i t e low ( moiety. The half l i f e of the former i s 4 to 12 hr and i s suggested to originate from the amide linkages carbonyl groups. The l a t t e r s half l i f e i s 660 hr and i s from the two of the six carbons of i t s aromatic rings. 4

48

1

0

8

2

1

1

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

338

Table

fit

Photooxidation Rates at 100°C of Pseudo F i r s t Order Decarboxylations

Plots of 1/2 0 & θ 2 concentrations v s . ι photolysis times* Τ 12 Γ Ί 8

Ί8

2

Photolysis Solar rates , rates (mole sec ) (mole sec~') 0

c

1.65 χ 1 0 '

9

3.28 χ Ι Ο "

5.82 χ Ι Ο "

s

4

1 2

1 2

1.32 χ Ι Ο "

2.62 χ Ί Ο "

11

Rate constants of 2nd order photooxidation of Kevlar Kevlar in 0.2 atm l^Oo at 100°C Π mol?-' sec-î) 0d

4.18 χ Ι Ο "

8

14

4.67 χ Ι Ο "

1 4

2.01 χ Ι Ο "

1 0

4 5.04 χ Ι Ο "

0

TÔ

26

1 3

4.03 χ 1 Ô

15

30

Photolysis Time, min Ά'

designates decarboxylation temperature at 196°C and ' B ' at 250C.

^Photolysis rates are expressed as moles of -4-C7H5NO-4-/photolysis times (sec). c

d

S o l a r rates are photolysis rates/125.

The i n i t i a l concentrations of -4-C7H5NO-4- to produce 1/2 0 ( i . e . , to luce produce 4 6 o product) i s 6.1 mole I' and to produce ' ° 0 ? ' ( i . e . , to prod-. 48co? product) is 12.2 mole 1-1 using the density of Kevlar at 1.45 g/cm . The ' 0 i s assumed as an ideal gas at 100°C and 0.2 atm. The 0.415 g Kevlar -29 fabric expressed as -(-CyH^NO-)- moieties in moles i s 3.49 χ 1 0 ' moles. 1 8

2

2

1

3

8

2

3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

24.

T O Y AND STRINGHAM

Photodegraded p-Aramid

F i g u r e 5. P l o t s o f oxygen-18 c o n c e n t r a t i o n v e r s u s p h o t o l y s i s time of pseudo f i r s t o r d e r d e c a r b o x y l a t i o n s a t 196°C f o r 20 min from t h e top s u r f a c e l a y e r .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

339

340

CHEMICAL REACTIONS ON POLYMERS

Table IV, Summary Data on the Two Major Photooxidative Degradation Rate Constants and Activation Energies

8

Photolysis Temperatures °C

°K

Rates

ÎOOOA

I. From plots of 1/2

Solar Rates

b

(mole s e c " ) 1

1 8

0

2

25

398

3.356

373 398

2.681 2.513

1.65 7.76

X

10" ΙΟ"

150

423

2.364

9.69

X

10"

0

?

1

Rate Constants* (1 mole"

1

1

sec" ) 1

Activation Energies® (kcal mole" ) 1

(i.e.

100 125

I I . From plots of

0

(mole s e c " )

X

(i.e.,

9

1.32 X ίο6.21 X ΙΟ"

11

11

9

9

7.75

X

Hf

1 1

1.10

X

o-

4.18 1.96

X

Ο"

X

Ο"

2.36

X

14)),

(15).

Thus,

while 0

There i s

from t h a t o f s i n g l e t

a need t o s t u d y

a family of c l o s e l y

2

the

3

initial

i n degradation o f those polymers. paper examines ent cial

reactions

3

of 0( P)

3

role of

0( P)

polymers

oxygen.

the mechanisms o f 0 ( P )

r e l a t e d polymers i n o r d e r t o

s t e p s commencing w i t h t h e

is

1

i n promoting c h e m i c a l changes i n u n s a t u r a t e d o r s a t u r a t e d s h o u l d be d i s t i n g u i s h a b l e

well-

double

reactions

identify

the

oxygen atom a t t a c k and c u l m i n a t i n g As a s t a r t

in this

with polybutadienes

direction, having

from the f a c t

Spe­

i n s t u d y i n g u n s a t u r a t e d h y d r o c a r b o n polymers

derives

t h a t oxygen a t o m - o l e f i n

the

3

extensively studied class of 0( P)

reactions

reactions

constitute

(5,16),

tation products.

Thus,

the m a c r o m o l e c u l a r c o u n t e r p a r t s o f

fragmen­ these

r e a c t i o n s might be more r e a d i l y o b s e r v e d and i n t e r p r e t e d than produced i n s a t u r a t e d p o l y m e r s w h i c h , by a n a l o g y (5),

s h o u l d i n v o l v e m a i n l y p r o c e s s e s ensuant T h e r e i s added i n t e r e s t

cis-1,4-polybutadiene that t h i s

a process

those

alkanes

(17,18)

i n the c o r r e s p o n d i n g cis-2-butene

with

reported

i s o m e r i z a t i o n on exposure

l o w - m o l e c u l a r weight a n a l o g u e ,

hydro­

3

reaction of 0( P)

Rabek and c o - w o r k e r s

not observed

to simple

on a b s t r a c t i o n o f

i n e x a m i n i n g the

polymer underwent c i s - t r a n s

a t o m i c oxygen, with i t s

since

most

c h a r a c t e r i z e d by

the f o r m a t i o n o f e p o x i d e s and c a r b o n y l compounds as w e l l as

gen.

this

differ­

1 , 4 / 1 , 2 c o n t e n t s and w i t h t h e i r p o l y a l k e n a m e r homologues. interest

with

various

to

reaction

(19,20).

Experimental Polymers.

The polymers used

1,4-polybutadienes

in this

study comprised c i s -

and t r a n s -

(CB and T B ) , amorphous 1 , 2 - p o l y b u t a d i e n e

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

(VB), a

344

CHEMICAL REACTIONS ON POLYMERS 1,4/1,2 contents,

number o f p o l y b u t a d i e n e s w i t h d i f f e r e n t pentenamer

(TP), cis

ethylene-propylene

and t r a n s p o l y o c t e n a m e r s

r u b b e r (EPM),

trans

the s t r u c t u r e s and s o u r c e s

a r e i n d i c a t e d i n T a b l e s I and I I .

poly-

(CO and T O ) , and o f which

A l l o f t h e s e p o l y m e r s were

elasto­

mers e x c e p t f o r the h i g h l y c r y s t a l l i n e TB and the p a r t i a l l y ( 3 3 ? ) c r y s t a l l i n e TO. benzene

The polymers were p u r i f i e d

T B , c a s t from benzene KBr d i s k s

stock solutions

to a thickness 3

ature to 0 ( P )

o f -5-15

3

and

F i l m s o f C B , VB, and

onto 0 . 5 - i n c h d i a m e t e r NaCI o r

ym, were exposed a t ambient

f o r various periods of time.

i n f r a r e d s p e c t r a o f these f i l m s , 0( P),

by r e p r e c i p i t a t i o n from

s o l u t i o n u s i n g methanol as p r e c i p i t a n t .

b e f o r e and a f t e r

were o b t a i n e d w i t h a P e r k i n - E l m e r Model 621

an IBM IR/85 S p e c t r o m e t e r w i t h ATR a t t a c h m e n t

crystal),

respectively.

above were a l s o weight,

Thin films of a l l

r e a c t i o n with spectrophotometer (zinc

selenide

the p o l y m e r s mentioned

c a s t onto g l a s s c o v e r s l i p s

and s u b j e c t e d

temper­

T r a n s m i s s i o n and ATR

d r i e d to

constant

t

weight o f each c o v e r s l i f i l m was ~10 mg, and i t s

s l i p p l u s f i l m b e f o r e and a f t e r Cahn e l e c t r o b a l a n c e 3

0( P)

Reactor.

(99.99? 0 ) 2

r a d i o - f r e q u e n c y power s u p p l y .

the

beyond the The

flow

1) d r i v e n by a 13.56-MHz

Power, s u p p l i e d t h r o u g h a m a t c h i n g ( 3 . 9 7 cm χ 1.59 To p r e v e n t

Additionally,

cm; 1.59

cm a p a r t )

i n - l i n e exposure o f

the samples were l o c a t e d

the

t a i l o f any v i s i b l e glow,

which ended b e f o r e

At an 0

flow r a t e o f 6 . 5 χ 10~

2

r e a c t o r p r e s s u r e o f 73 Pa ( 0 . 5 5 power l e v e l χ 10-

sion of 0

2

2

of cm

3

the b e n d .

3

times

described

(STP)/s,

t o r r ) w i t h the d i s c h a r g e o f f ,

( S T P ) / s ; the l a t t e r

to 0 atoms.

(0.8

cm

15 W, the flow r a t e o f 0 atoms was found t o

the polymer samples least eight

2

discharge

12.7 cm

0 atom f l o w r a t e was measured by NO2 t i t r a t i o n as

elsewhere ( 2 1 ) .

and a

be

f i g u r e r e p r e s e n t e d an 18? c o n v e r ­ 3

Assuming complete 0 ( P ) - i n d u c e d o x i d a t i o n

to C 0

2

and H 0 , the f l o w r a t e o f 0 atoms was 2

t h a t r e q u i r e d to m a i n t a i n the h i g h e s t

etch

of at

rate

2

mg/cm -h, in T B ) .

Polymer sample t e m p e r a t u r e , measured w i t h a thermocouple a t e d beneath a t h i n g l a s s p l a t f o r m s u p p o r t i n g the s a m p l e , e t c h r a t e o f the p o l y m e r ; the maximum t e m p e r a t u r e r i s e any

cover

i n a p a r a l l e l - p l a t e plasma

in Figure

i n the plasma r e a c t o r between the o r i g i n o f the

the s a m p l e .

observed

of

was measured w i t h a

t o u l t r a v i o l e t r a d i a t i o n from the p l a s m a , a r i g h t - a n g l e bend

was l o c a t e d

2.4

3

t o the e x t e r i o r w a l l o f the g l a s s r e a c t o r , was measured by a

B i r d Model 43 r f - w a t t m e t e r .

and

The w e i g h t

to 0 ( P )

Oxygen atoms were produced from Matheson Gas P r o d u c t s

network to copper e l e c t r o d e s

samples

exposure

( i l l u s t r a t e d schematically

attached

cm .

t o a p r e c i s i o n o f ± 0 . 0 1 mg.

u l t r a - h i g h p u r i t y oxygen reactor

2

a r e a was 2.5

run was 9 K , e x h i b i t e d by TB a f t e r

20 min e x p o s u r e

situ­

depended on

encountered 3

to 0 ( P ) .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

in The

25. G O L U B E T A L . temperature r i s e longed

Reaction of Atomic Oxygen

345

f o r most samples was i n s i g n i f i c a n t

even a f t e r

pro­

exposure.

R e s u l t s and D i s c u s s i o n Infrared

Indications of Etching.

undergoes 3

0( P),

substantial

t a i n l y no c i s - t r a n s

isomerization.

bands, w h i l e

1,4 bands a t

Thus,

intensities

the r e l a t i v e

(or

the

transmission

IR s p e c t r a

increased transmittance)

intensities

of

13.6 and 10.3 ym, r e s p e c t i v e l y ,

are unchanged.

that

the r e a c t i o n o f 0 ( P )

3

w i t h polymer f i l m s a t ambient layers

of

the c i s - 1 , 4 and t r a n s -

i m p l i e s what had been n o t e d by p r e v i o u s w o r k e r s ( 6 , 9 ) «

c o n f i n e d t o the s u r f a c e

to

and c e r ­

also is

CB f i l m

on p r o l o n g e d e x p o s u r e

w i t h no i n d i c a t i o n s o f any m i c r o s t r u c t u r a l changes

show g r e a t l y d e c r e a s e d all

As may be seen i n F i g u r e 2,

t h i n n i n g , or e t c h i n g ,

T h i s view

is

Figure 2 namely,

temperature

r e i n f o r c e d by

the

c o r r e s p o n d i n g ATR IR s p e c t r changes

i n the e t c h e d C

spectra are e s s e n t i a l l y i s no need t o p r e s e n t

the same as

them h e r e .

new a b s o r p t i o n a t 2 . 8 ym ( - 0 0 H ) , singlet 1

0 -reacted 2

transmission spectra,

which would i n d i c a t e

3

oxygen

the

i n the 0 ( P ) - i n d u c e d

etching,

involvement

of

a l t h o u g h ATR s p e c t r a

of

CB f i l m s have d i s p l a y e d s u c h a b s o r p t i o n

Figure 2 c e r t a i n l y d i f f e r s r e p o r t e d t o be CB f i l m exposed

(13»14).

from F i g u r e 2c i n R e f e r e n c e t o a t o m i c oxygen g e n e r a t e d

photosensitized

decomposition o f N 0 .

recognized that

t h e i r observed c i s - t r a n s

2

been due i n s t e a d

2

They s u p p o r t e d t h i s 15 min t o N 0

17) which i n d e e d showed N 0 with c i s - t r a n s

F i g u r e 3 which p r e s e n t s exposure

to N 0

2

for

2

(!)

2

of

of

view by e x h i b i t i n g

1 atm ( F i g . 4 i n

T h a t view

is

changes

c o n f i r m e d by

o u r IR s p e c t r a o f CB f i l m b e f o r e and a f t e r

15 s

N 0 - r e l a t e d bands a t 6 . 1 2 ,

at

reduced p r e s s u r e

6.45,

7.40,

isomerization (strong

i n he t r e a t e d C B ) .

at

2

groups

2

bands as w e l l as s p e c t r a l

isomerization.

i s v e r y s i m i l a r t o Rabek and c o - w o r k e r s with evidence

Actually,

1

atm); Figure 3

(0.42

Figure 4 in that

7.80,

it

and 11.8 ym,

1 0 . 3 - and weak

shows

together

13.6-ym bands

the N 0 - i n d u c e d c i s - t r a n s

isomerization

2

CB had been r e p o r t e d 25 y e a r s ago by S o v i e t w o r k e r s ( 2 2 ) .

ever,

the p r e s e n t work c l e a r l y demonstrates

3

that 0 ( P )

polymer nor any c i s - t r a n s shows t h a t TB l i k e w i s e 3

film,

i s a new,

surface

i n the

i s o m e r i z a t i o n ; i n the v e r y t h i n ,

weak band a t

12.6 ym, the a s s i g n m e n t

bulk

Figure 4

For completeness,

undergoes e x t e n s i v e e t c h i n g on e x p o s u r e

w i t h no t r a n s -»· c i s there

isomerization.

How­

causes

e t c h i n g o f C B , w i t h no o b s e r v a b l e m i c r o s t r u c t u r a l changes

0( P),

since

2

IR s p e c t r a o f CB exposed

Ref.

(17)

i s o m e r i z a t i o n might have

t o N 0 , a b y p r o d u c t o f the N 0 d e c o m p o s i t i o n ,

a t t a c h e d t o the CB b a c k b o n e .

associated

17,

by mercury

Rabek and c o - w o r k e r s

the c i t e d f i g u r e showed v a r i o u s bands a t t r i b u t a b l e t o N 0 the

there

N e i t h e r o f t h e s e s p e c t r a show any

to

e t c h e d TB o f which

i s as y e t unknown, i n d i c a t i n g minor m i c r o s t r u c t u r a l m o d i f i c a t i o n o f this

p o l y m e r , presumably a t o r near the s u r f a c e .

sion

IR s p e c t r a o f the o t h e r polymers s t u d i e d show o n l y the

of

f i l m - t h i n n i n g or etching,

S i n c e the

they were o m i t t e d from t h i s

transmis­ effects

paper.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

346

CHEMICAL REACTIONS ON POLYMERS

ELECTRODES

Figure 1.

3

Apparatus f o r exposure o f polymer films to 0 ( P ) .

Λ

τΛ/

3500

3000

2500

r

WAVELENGTH, μηι 6 7 1 r

1800

1600

1400 1200

1000

800

600

WAVENUMBER, cm"

1

Figure 2.

Transmission IR spectra o f CB f i l m on KBr before ( and a f t e r (—) exposure to 0 ( P ) for 16 h. 3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

)

25.

G O L U B E T AL.

347

Reaction of Atomic Oxygen

WAVELENGTH, μτη 6 7

100,

8

9 10

12 15 —ι—ι ι ι ι

80 λ

i j»

Ι» '

60 < t 40 h CO Ζ < 20 oc ι

3500

ι

I

ι ι ι ι

3000

I/LJ

2500

I

I

1800

U L L

1600

1

1

L

1400

I

1200

L

1000

800

600

WAVENUMBER, cm"

1

Figure 3 .

Transmission and a f t e r

IR s p e c t r a o f CB f i l m on NaCl b e f o r e

(—) exposure t o N 0 a t reduced 2

(

)

pres­

s u r e f o r 15 s .

WAVELENGTH, μ η

I

3500

ι

3000

2500

l

V

1800

I

I

1600

I

I

1400

I

I

1200

I

A 10.3

Li—I

1000

1

800

1

600

WAVENUMBER, cm"

1

F i g u r e 4.

Transmission and a f t e r

IR s p e c t r a o f TB f i l m on KBr b e f o r e 3

(—) exposure t o 0 ( P ) f o r 4 . 5 h .

American Chemical Society Library 1155 16th St., N.W.

In Chemical Reactions on Polymers; Benham, J., et al.; Washington, D.C.Society: 20036Washington, DC, 1988. ACS Symposium Series; American Chemical

(

)

CHEMICAL REACTIONS O N POLYMERS

348 Weight-Loss I n d i c a t i o n s o f E t c h i n g . butadienes

f o r 0 ( P ) - i n d u c e d weight

and p o l y a l k e n a m e r s .

T a b l e s I and I I .

loss in various

From s u c h p l o t s ,

obtained for a family o f c l o s e l y in

F i g u r e 5 shows t y p i c a l z e r o -

3

order k i n e t i c plots

r e l a t e d polymers and a r e summarized

F o r unknown r e a s o n s ,

the k i n e t i c p l o t s

e r a l o t h e r polymers (not shown i n the f i g u r e ) periods,

b u t the p l o t s were a l m o s t always

e r o s i o n commenced.

exhibited

example may be found i n F i g u r e

l i n e a r once the of

this

paper.

1 o f R e f e r e n c e 9,

sev­

surface

p l o t w i t h an i n t e r c e p t on the

Another

which shows z e r o -

t h r o u g h the o r i g i n f o r f o u r d i f f e r e n t

straight-line

for

induction

An example o f a p l o t w i t h an i n d u c t i o n p e r i o d may

be seen i n F i g u r e 4 o f the p r e p r i n t (23) order p l o t s

poly-

e t c h r a t e d a t a were

p o l y m e r s , and a

time-axis

for a

fifth

polymer. A l t h o u g h e t c h r a t e d a t a f o r a p a r t i c u l a r polymer f i l m straight-line any by

kinetic plots,

yielded

the d a t a from one f i l m t o a n o t h e r

for

g i v e n polymer e x h i b i t e the l a r g e s t a n d a r d d e v i a t i o n

scatter,

the cause o f which i s under i n v e s t i g a t i o n ,

d a t a r e p o r t e d h e r e have o n l y s e m i q u a n t i t a t i v e As may be seen from the d a t a o f T a b l e u n i t s has a marked e f f e c t

I,

on the e t c h r a t e s

the e t c h

rate

significance. the p r e s e n c e

for

of

vinyl

polybutadienes,

d e c r e a s i n g by about two o r d e r s o f magnitude from CB ( w i t h 2% v i n y l units)

to V22-V40,

thereafter

VB ( w i t h 97% v i n y l u n i t s ) . 3

effects of 0( P)

remaining s u b s t a n t i a l l y

T h i s demonstrates

r e a c t i o n w i t h the

1,4

constant

a t once t h a t

and 1,2

up

d o u b l e bonds a r e

not

a d d i t i v e and t h a t the v i n y l groups i m p a r t a s p e c i a l p r o t e c t i o n polybutadienes,

to

the

u n f o r t u n a t e l y , a sample o f CB w i t h no v i n y l

to

double

bonds c o u l d n o t be o b t a i n e d f o r comparison w i t h the v i n y l - f r e e

poly­

alkenamers

have

(Table I I ) ,

but such a polymer would be e x p e c t e d

an e t c h r a t e somewhat h i g h e r than the v a l u e Table I. cis

i n d i c a t e d f o r CB i n

T h a t the e t c h r a t e f o r TB i s about s i x

isomer,

CB, i s

believed

between the r e s p e c t i v e

times

to be due t o a morphology

polymers:

to

that of

scanning e l e c t r o n micrographs

showed the h i g h l y c r y s t a l l i n e TB f i l m t o have a much g r e a t e r roughness The

than the amorphous o r e l a s t o m e r i c d a t a o f T a b l e II

indicate that

EPM was chosen fully

in vinylene

the e t c h r a t e s

(-CH=CH-) u n s a t u r a t i o n .

CB t o a v o i d a morphology f a c t o r

was o b s e r v e d w i t h c r y s t a l l i n e T B .

The d i f f e r e n c e

the p a r t i a l l y c r y s t a l l i n e TO and the e l a s t o m e r i c 1.2:1.0)

rates

than t o the d i f f e r e n c e

C i s / t r a n s content

had l i k e w i s e

The e l a s t o m e r i c

in etch rates,

was a s m a l l e f f e c t , the v i n y l

for

about

between

in their cis/trans (see

the as

in etch rates CO ( r a t i o o f

no p e r c e p t i b l e e f f e c t

i n the v i n y l - c o n t a i n i n g p o l y b u t a d i e n e s

its

monotonically

as a model f o r

i s a t t r i b u t a b l e more t o a morphology d i f f e r e n c e

these polyoctenamers tent.

f o r CB and

increase

instead of c r y s t a l l i n e polyethylene

'saturated'

surface

CB f i l m .

"homologues"—TP, CO ( o r T O ) , and EPM—tend t o with a decrease

its

difference

Table I ) ;

con­

on

etch

if

there

i t was c e r t a i n l y masked by the dominant e f f e c t

groups.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

of

GOLUB ET AL.

0

Figure 5.

Reaction of Atomic Oxygen

1

2 3 4 5 TIME OF EXPOSURE, h

Typical kinetic

6

7

3

p l o t s f o r 0 ( P ) - i n d u c e d weight

in various polybutadienes

and p o l y a l k e n a m e r s .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

loss

350

CHEMICAL REACTIONS ON POLYMERS

Table I .

E t c h Rate Data f o r V a r i o u s

? Double bonds Polymer**

c i s - 1 ,4

trans-1,4

Polybutadienes

Etch rate

a

Source

2

mg/cm -h

Vinyl

TB

2

96

2

0.80

± 0.40

Goodrich

CB

96

2

2

0.132

± 0.011

Polysar

d

V4

20

76

4

0.093

± 0.011

GenCorp

e

V7

48

V10

47

V11

47 40

42

11

0.092

V22

38

22

0.0016 ± 0.0012

V33 V40

31 28

36

33

32

40

0.0046 ± 0.0053 0.0028 ± 0.0016

V70

15

15

70

V82

9 2

9 1

82

0.0015 ± 0.0006 0.0020 ± 0.0012

97

0.0022 ± 0.0007

VB

GenCor

a

-CH CH=CHCH -...-CH CH(CH=CH )-...

b

V4

2

0

2

2

± 0.050 GenCorp Firestone GenCorp Goodyear^ Firestone Firestone

2

t h r o u g h V82 d e n o t e

polybutadienes

with indicated

vinyl

contents. c

Mr.

J . J . Shipman ( d e c ) ,

BFGoodrich Research C e n t e r , B r e c k s v i l l e ,

OH. d

Dr.

e

Dr.

I. G. Hargis,

f

Dr.

T . A . A n t k o w i a k , The F i r e s t o n e T i r e & Rubber C o . , A k r o n , OH.

g

Dr.

A . F . H a l a s a , Goodyear T i r e & Rubber C o . , A k r o n , OH.

S . E . H o m e , P o l y s a r I n c . , Stow, OH. GenCorp,

A k r o n , OH.

A sample o f p a r t i a l l y h y d r o g e n a t e d V70 (same s o u r c e a s V70; see Table I ) , hydrogenated with a p r o p r i e t a r y c a t a l y s t , ined. and

T h i s polymer, designated

10? 1,2 d o u b l e b o n d s ,

p r i s i n g 5? h y d r o g e n a t e d The

exam­ trans-1,4

1,2 d o u b l e b o n d s .

reduced v i n y l

2

found t o be 0.010 m g / c m - h , o r a b o u t seven t i m e s is consistent

12?

t h e r e m a i n i n g s a t u r a t e d monomer u n i t s com­

1,4 and 60? h y d r o g e n a t e d

e t c h r a t e f o r HV70, w i t h i t s g r e a t l y

result

was a l s o

HV70, had 13? c i s - 1 , 4 ,

content,

that o f V70.

with the above-mentioned o b s e r v a t i o n t h a t

d o u b l e bonds p r o t e c t p o l y b u t a d i e n e a g a i n s t

3

0( P)-induced

was This 1,2

etching.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

25. G O L U B E T A L . Table I I .

Reaction of Atomic Oxygen

351

E t c h Rate Data f o r c i s - 1 , 4 - P o l y b u t a d i e n e Homologues

and

its

a

Double bonds/

Distribution of

carbon Polymer

atom

CB

0.25 0.20

TP CO

0.125

TO

0.125 0

EPM

a

d o u b l e bonds % cis

2

2

0.132

±

0.011

Polysar**

17 81

83

-

0.240 ±

0.016

Goodyear

-

19 80

20

0.293 ± 0.009

Huls

0.355

Hul

0.049

0

d

x

n

χ = 2 ( C B ) , 3 ( T P ) , 6 (CO, T O ) , » (EPM,

with 2.4:1.0 ethylene-propylene fully

Source

2

96

-[CH=CH-(CH ) ] -; 2

Etch rate mg/cm -h

% Vinyl

% trans

saturated

molar r a t i o — a q u a s i model f o r

the

polyalkenamer).

b

Dr.

S.

c

Dr.

E . A . O f s t e a d , Goodyear T i r e & Rubber C o . , A k r o n , OH.

d

Dr.

E . 0.

E . Home, Polysar Corp., E . Siebert,

A k r o n , OH.

Huls C o r p . ,

Piscataway, N J .

Mechanistic Considerations To account f o r the major f i n d i n g s tive

effect of vinyl units

in this

work, namely,

in 1,4-/1,2-polybutadienes

the

and

increased etch rate with decrease in vinylene unsaturation p o l y a l k e n a m e r s , we i n v o k e the g e n e r a l l y 3

reaction of 0( P)

with simple o l e f i n s .

C v e t a n o v i c some 25 y e a r s ago 3

addition of 0( P)

the

T h i s mechanism,

and r e c e n t l y

updated ( 1 6 ) ,

pressure-independent

The "hot" p r o d u c t s i n t u r n a r e e i t h e r (PDF).

biradical

collisionally

PDF, which i s

or c a r ­

deacti­

pressure-

completely

suppressed

a t h i g h p r e s s u r e o r i n condensed m e d i a , would be u n i m p o r t a n t i n c a s e o f polymer f i l m s .

P I F , however,

which i s

i n condensed media a t c r y o g e n i c t e m p e r a t u r e s tant

3

in 0( P)

ture, tions.

reactions

i f PIF o c c u r s

completely

(),

d o u b l e bonds i s assumed

initially

at

epox­

to c h a i n r u p t u r e a n d / o r

a c c o r d i n g t o the

scheme:

-CHo—CH=CH—C

-CHo—CH -

I •O—CH—CH » 2

(MINOR) -CH

—ÇH—CHO

2

+

»CH 2

(CHAIN R U P T U R E )

PIF

OR

-CHo —CH -

-CHo—CH —C—CH

C = 0 + Η·

I CH « 2

(NO C H A I N R U P T U R E )

3

Whereas 0 ( P )

(NO C H A I N R U P T U R E )

CROSSLINKS

a d d i t i o n t o the

1,2

c h a i n r u p t u r e , a d d i t i o n t o the

(CROSSLINKING POTENTIAL)

d o u b l e bond has no d i r e c t r o u t e

1,4

d o u b l e bond d o e s .

to

Such c h a i n

r u p t u r e would be a p r e c u r s o r t o polymer f r a g m e n t a t i o n and w e i g h t loss, the

while c r o s s l i n k i n g — a p o t e n t i a l

1,2

d o u b l e bond—would c o u n t e r a c t

t e c t " t h e polymer a g a i n s t lower e t c h r a t e than the and 1,2

the

the b i r a d i c a l

unit,

1,4-polybutadiene

CB.

for

formed from the

thus

VB had a much

For polybutadienes

1,4

- C H - (generated 2

1,2

The l e v e l i n g o f f

e x c e s s o f -20? s u g g e s t s t h a t

t h a t can p r o p a g a t e the

d o u b l e bond c o n t e n t of the

i n PIF

d o u b l e bond) o n t o a nearby

T h i s can a c c o u n t f o r the s h a r p d r o p i n e t c h

p o l y b u t a d i e n e s as the

to - 2 0 - 4 0 ? .

to "pro­

d o u b l e b o n d s , a d d i t i o n a l c r o s s l i n k i n g can o c c u r

f o r m i n g a new p o l y m e r i c r a d i c a l

linking process.

addition

T h i s scheme can

1,2-polybutadiene

t h r o u g h a t t a c k o f the m a c r o m o l e c u l a r r a d i c a l of

3

from 0 ( P )

f r a g m e n t a t i o n and t h e r e b y

surface erosion.

a c c o u n t f o r the f i n d i n g t h a t w i t h b o t h 1,4

result

is

rates

i n c r e a s e d from 2

the e t c h r a t e f o r v i n y l "protective

vinyl

cross-

contents

c a p a c i t y " o f the

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

in

vinyl

25. G O L U B E T A L .

Reaction of Atomic Oxygen

groups by c a p t u r i n g the n a s c e n t vinyl

-CH radicals is

reached a t

2

that

content. A l t h o u g h hydrogen a b s t r a c t i o n 3

factor ing

353

in 0( P)

reactions

could r e s u l t

vinyl unit.

is

not expected

with polybutadienes,

from a b s t r a c t i o n o f

The r e s u l t i n g ,

the

resonating

-CH -C-CH=CH 2

t

2

t o be an i m p o r t a n t

additional

crosslink-

t e r t i a r y hydrogen i n

the

radical:

-CH -C=CH-CH 2

2

I

I

could readily attack a v i n y l

d o u b l e bond i n a n o t h e r polymer

molecule

t o produce a c r o s s l i n k and a new p r o p a g a t i n g polymer r a d i c a l . process

would have the e f f e c t

mentation,

since

of protecting

c r o s s l i n k e d polymers a r e more r e s i s t a n t

than a r e t h e i r u n c r o s s l i n k e d c o u n t e r p a r t s

This

the polymer a g a i n s t to

frag­

etching

(6)

To e x p l a i n the p r o g r e s s i v i n u n s a t u r a t i o n i n the p o l y a l k e n a m e r s , m e n t a t i o n p r o c e s s e s subsequent efficient

than f r a g m e n t a t i o n

d o u b l e bonds. the

3

rate constant

for 0( P)

frag 3

p r o c e s s e s ensuant

T h i s view f o l l o w s

f u l l y s a t u r a t e d EPM i s

postulat

to hydrogen a b s t r a c t i o n a r e much more

-2.6

from the

on 0 ( P )

fact

times that

that

f o r C B , even though

«135-175

t i m e s the

rate constant

gen a b s t r a c t i o n from a t e r t i a r y C - H bond ( i n a l k a n e s ) the -CH=CH-

amers,

the

from

for

(5,16).

d o u b l e bonds become f a r t h e r a p a r t i n the

χ = 2 to » .

increasing etch rate

in

hydro­ Thus,

translates

i n the homologous

The hydrogen a b s t r a c t i o n

for

polyalken­

i n c r e a s i n g l i k e l i h o o d f o r hydrogen a b s t r a c t i o n

into a progressively

to

the

a d d i t i o n t o the v i n y l e n e d o u b l e bond (as

c i s - 2 - b u t e n e ) a t 298 Κ i s as

addition

the e t c h r a t e

series

reaction:

0 + RH -> · 0 Η + Rmust be r a p i d l y

followed

by: R. + 0

R0-*

S i n c e a l k o x y r a d i c a l s a r e known p r e c u r s o r s t o c h a i n s c i s s i o n autoxidation

(24),

undergo f a c i l e is

the

in

"hot" a l k o x y r a d i c a l s formed as shown s h o u l d

chain s c i s s i o n

or fragmentation.

i l l u s t r a t e d f o r the a l k o x y r a d i c a l

e t h y l e n e o r p r o p y l e n e monomer u n i t -CH -C(R)(0-)-CH -* 2

2

The c h a i n

d e r i v e d from e i t h e r

scission the

i n EPM: _* - C H - C ( = 0 ) - R + - C H -

where R i s

2

Η or C H

2

3

Conclusions The major f i n d i n g s o f t h i s protective

effect

study are that v i n y l

in polybutadienes

against

3

groups e x e r t

0( P)-induced

a strong

etching,

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS O N POLYMERS

354

that

the e t c h

r a t e s f o r the p o l y a l k e n a m e r s

-CH=CH- u n s a t u r a t i o n , surfaces, diene

and t h a t

films

that

there

the

reactions

i s no c i s - t r a n s

i n the b u l k on e x p o s u r e

mechanism f o r r e a c t i o n s

3

of 0( P)

the u n s a t u r a t e d p o l y m e r s . polybutadienes double bonds,

is

explained

increase with decrease

are confined

isomerization of

t o a t o m i c oxygen.

with simple o l e f i n s

The p r o t e c t i v e

effect

is

applied

to in

through a b s t r a c ­

i n the v i n y l monomer u n i t s .

r a t e d a t a f o r the p o l y a l k e n a m e r s a r e a c c o u n t e d

a high

polybuta-

The C v e t a n o v i c

i n p a r t by c r o s s l i n k i n g t h r o u g h t h e s e

t i o n o f t e r t i a r y hydrogen atoms

the d o u b l e b o n d , the

in

polymer

o f the v i n y l s

and i n p a r t by c r o s s l i n k i n g i n i t i a t e d

increasing competition

t o the

The e t c h

f o r on the b a s i s

of

between hydrogen a b s t r a c t i o n and a d d i t i o n

former p r o c e s s

giving rise

to fragmentation

to with

efficiency.

Acknowledgments The a u t h o r s a r e g r a t e f u T a b l e s I and II in

this

for their g i f t s

of

the v a r i o u s polymer samples

used

study.

Literature Cited 1. Visentein, J. T.; Leger, L. J.; Kuminecz, J. F.; Spiker, I. K. Paper 85-0415, AIAA 23rd Aerospace Sciences Meeting, January 1985, and references cited therein. 2. Zimcik, D. G.; Tennyson, R. C.; Kok, L. J.; Maag, C. R. Eur. Space Agency Spec. Publ., 1985, ESA SP-232; Chem. Abstr. 1986, 104, 149894, and references cited therein. 3. Banks, Β. Α.; Mirtich, M. J.; Rutledge, S. K.; Swec, D. M. Thin Solid Films 1985, 127, 107. 4. Arnold, G. S.; Peplinski, D. R. AIAA J. 1985, 23, 1621. 5. Huie, R. E.; Herron, J. T. Prog. Reaction Kinetics 1975, 8, 1. 6. Hansen, R. H.; Pascale, J. V.; De Benedictis, T.; Rentzepis, P. M. J. Polym. Sci. 1965,A3,2205. 7. Taylor, G. N.; Wolf, T. M. Polym. Eng. Sci. 1980, 20, 1087. 8. Ueno, T.; Shiraishi, H.; Iwayanagi, T.; Nonogaki, S. J. Electrochem. Soc. 1985, 132, 1168. 9. MacCallum, J. R.; Rankin, C. T. Makromol. Chem. 1974, 175, 2477. 10. Lawton, E. J. J. Polym. Sci., A-1, 1972, 10, 1857. 11. Westenberg, Α. Α.; de Haas, Ν. J. Chem. Phys. 1964, 40, 3087. 12. Golub, M. A. Pure Appl. Chem. 1980, 52, 305. 13. Kaplan, M. L.; Kelleher, P. G. J. Polym. Sci., A-1, 1970, 8, 3163; Rubber Chem. Technol. 1972, 45, 423. 14. Rabek, J. F.; Ranby, B. J. Polym. Sci., Polym. Chem. Ed. 1976, 14, 1463. 15. Carlsson, D. J.; Wiles, D. M. J. Polym. Sci., Polym. Chem. Ed. 1974, 12, 2217.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

25.

GOLUB ET AL.

Reaction of Atomic Oxygen

355

16. Cvetanović, R. J . ; Singleton, D. L. Rev. Chem. Intermed. 1984, 5, 183. 17. Rabek, J. F.; Lucki, J . ; Rånby, B. Eur. Polym. J. 1979, 15, 1089. 18. Rabek, J. F.; Ranby, B. Photochem. Photobiol. 1979, 30, 133. 19. Klein, R.; Scheer, M. D. J. Phys. Chem., 1966, 72, 616. 20. Cvetanovio, R. J. Advan. Photochem., 1963, 1, 115. 21. Kaufman, F.; Kelso, J. R. In 8th Symposium (International) on Combustion; The Combustion Institute, Williams and Wilkins: Baltimore, 1960, p. 230. 22. Ermakova, I. I.; Dolgoplosk, Β. Α.; Kropacheva, Ε. N. Dokl. Akad. Nauk. USSR 1961, 141, 1363; Rubber Chem. Technol. 1962, 35, 618. 23. Golub, Μ. Α.; Lerner, N. R.; Wydeven, T. Polym. Prepr. 1986, 27 (2), 87. 24. Shelton, J. R. Rubbe R E C E I V E D August 2 7 , 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 26

Tri-n-butyltin Hydride Reduction of Poly(vinyl chloride) Kinetics of Dechlorination for 2,4-Dichloropentane and 2,4,6-Trichloroheptane 1

Fabian A. Jameison , Frederic C. Schilling, and Alan E. Tonelli AT&T Bell Laboratories, Murray Hill, NJ 07974 2,4-Dichloropentan (TCH) were reductivel hydride ((n-Bu) SnH) directly in the NMR sample tube. C NMR spectra were recorded periodically to monitor the progress of DCP and TCH dechlorination. From these observations the following kinetic conclusions were drawn: i. meso (m) DCP was reduced 30% faster than racemic (r) DCP; ii. the Cl from DCP was removed 4 times faster than the Cl in 2-chloropentane or 2-chlorooctane; iii. the 4-Cl in mm-TCH is removed faster than the 4-Cl in mr-TCH which in turn is more reactive than the 4-Cl in the rr isomer; and iv. the 4-Cl in TCH is removed 1.5 times faster than the 2or 6-Cl's. Conclusions i. and ii. were previously observed at the diad level, at least qualitatively, in the (n-Bu) SnH reduction of poly(vinyl chloride) (PVC) to ethylene-vinyl chloride (E-V) copolymers. Using the kinetic information obtained from the reduction of DCP and TCH, an attempt was made to simulate the (n-Bu) SnH reduction of PVC to E-V copolymers. Comparison of the structures of the E-V copolymers simulated on the computer with those determined for (n-Bu) SnH reduced PVC by C NMR permits us to conclude that DCP and TCH are model compounds appropriate for studying the reductive dechlorination of PVC. 13

3

3

3

13

3

1 3

Starnes and Bovey ( l ) pioneered the method of C N M R analysis of reduced polyvinyl chloride) (PVC) to study the microstructure of P V C . Tri-n-butyltin hydride ((n-Bu) SnH) was found to completely dechlorinate P V C resulting in polyethylene (PE) whose microstructure (branching, end-groups, etc.) could be sensitively studied by C N M R . The present authors (2) subsequently produced a series of ethylene (E) - vinyl chloride (V) copolymers (E-V) by using less than the 3

1 3

1

Current address: Department of Chemistry, State University of New York at Stony Brook, Stony Brook, N Y 11794 0097-6156/88/0364-0356$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26.

Reduction of Poly (vinyl chloride)

JAMEISON ET AL.

357

stoichiometric amount of (n-Bu) SnH during the reductive dechlorination of P V C . Traditional means of obtaining E - V copolymers suffer from several shortcomings. Chlorination of P E (3) results in head-to-head (vicinal) and multiple (geminal) chlorination leading to structures which are not characteristic of E - V copolymers. Direct copolymerization of Ε and V monomers does not usually lead to random E - V copolymers covering the entire range of comonomer composition. Free-radical copolymerization (4,5) at low pressure yields E - V copolymers with V contents from 60 to 100 mol % . The 7-ray induced copolymerization (6) under high pressure yields E - V copolymers with increased amounts of E , but it appears difficult to achieve degrees of Ε incorporation greater than 60 mol % without producing blocky samples. The series of E - V copolymers obtained by partial reduction of P V C with (n-Bu) SnH were found (2) to have the same chain length as the starting P V C (~ 1000 repeat units). Their microstructures were determined by C N M R analysis (2) as indicated in Figure 1. The results of this analysis are presented in Table I in terms of comonomer diad and triad probabilities. A close examination interesting observations. First, as the amount of chlorine (CI) removed was increased, the ratio of racemic (r) to meso (m) W diads increased, and second the disappearance of W diads was greater than anticipated for the random removal of Cl's. Consequently, we concluded from the (n-Bu) SnH reduction of P V C to E - V copolymers and eventually to P E , that Cl's belonging to W diads are preferentially removed relative to isolated Cl's ( E V E ) and that m - W diads are reduced faster than r - W diads. Subsequent studies of the physical properties of this series of E - V copolymers obtained via the (n-Bu) SnH reduction of P V C have revealed that their properties, both in the solid state and in solution, are sensitive to their detailed microstructure (7-10). These observations prompted the present study concerning the mechanisms of the reductive dechlorination of P V C with (n-Bu) SnH. We have chosen the P V C diad and triad compounds 2,4dichloropentane (DCP) and 2,4,6-trichloroheptanefTCH) as subjects for our attempt to obtain quantitative kinetic data characterizing their (nBu) SnH reduction in the hope that they will serve as useful models for the reduction of P V C to E - V copolymers. Unlike the polymers ( P V C and E-V), D C P and T C H are low molecular weight liquids whose high resolution C N M R spectra can be recorded from their concentrated solutions in a matter of minutes. Thus, it is possible to monitor their (n-Bu) SnH reduction directly in the N M R tube and follow the kinetics of their dechlorination. Finally the kinetic data are compared to the microstructures of the E - V copolymers obtained by (n-Bu) SnH reduction of P V C to test the suitability of D C P and T C H as model compounds for P V C reduction. This is achieved by computer modeling the reduction of P V C to E - V copolymers with the aid of the kinetic parameters obtained from the study of D C P and T C H reduction, and then comparing the observed and modeled E - V microstructures. 3

3

1 3

3

3

3

3

1 3

3

3

E X P E R I M E N T A L M A T E R I A L S .

The 2-chloro-4-methylpentane, 2-chlorooctane, and 4-

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

358

CHEMICAL REACTIONS ON POLYMERS

(α) IOIOIOI

ΟΙΟΙΟΙΟ

VV =01010 VE =01000 EV =00010

EE = ( * * 0 0 0 * * - O I O O O ) / 2 * = 0 or I

J

EVE VVE EVV VVV VEV VEE EEV

L

EEE = [(0000000+0000001) -OOOOOIO]/2 OOOIO 01000

0101010

(b)

=0001000 =0101000 =0001010 =0101010 =0100010 =0100000 =0000010

0100010

L 0000000 000Ô001 01010

OOOQOIO 0I00000

OOOIO 01000

looogioi 0 100010

ι

ι

ι

ι

ι

I ι 60

ι

ι

ι

ι

ι

ι

ι ι

1 ι 50

ι

ι

ι

ι

ι

ppm

ι

ι

ι—I ι ι 40

ι—ι

;

ι

ι

ι

ι

1 ι ι 30

ι

ι

ι

J ι—L_J—L 20

vs(CH ) Si 3

4

1 3

Figure 1. 50.31 M H z C N M R spectra of P V C (a) and two partially reduced P V C ' s , E-V-84 (b) and E-V-21 (c). Please note the table of E - V microstructural designations in the upper right-hand corner of the Figure, where 0,1 = C H , CHC1 carbons. Resonances correspond to underlined carbons. The assignment of different stereosequences is given in reference 2. 2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26.

JAMEISON ET AL.

Reduction of Polyvinyl

chloride)

359

Table I Diad and Triad Probabilities for E-V Copolymers

Copolymer

Pvv

PVE " PEV

PEE

PEVE

PVVE " P E W

Pvvv

PVEV

E-V-85

.742

.124

.011

.015

.115

.619

.114

.011

0.0

E-V-84

.709

.134

.023

.025

.108

.615

.101

.019

.004

E-V-71

.470

.239

.052

.063

.175

.310

.175

.048

.008

E-V-62

.344

.278

.099

.116

.177

.177

.177

.075

.027

E-V-61

.343

.275

.107

.121

.173

.198

.141

.083

.029

E-V-60

.316

.285

.114

.141

.167

.154

.179

.077

.038

E-V-50

.200

.297

.205

.192

.133

.073

.166

.129

.045

E-V-46

.147

.309

.235

.205

.116

.037

.149

.140

.098

E-V-37

.087

.286

.342

.219

.078

.012

.115

.158

.183

E-V-35

.061

.278

.383

.224

.064

.015

.090

.168

.208

E-V-21

.014

.197

.593

.190

.016

0.0

.035

.153

.436

E-V-14

0.0

.127

.746

.104

0.0

0.0

.051

.123

.599

E-V-2

0.0

.025

.950

.021

0.0

0.0

0.0

.026

.926

PVEE •

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

PEEV

PEEE

360

CHEMICAL REACTIONS ON POLYMERS

chlorooctane were purchased from Wiley Organics and used as received. The 2,4-dichloropentane was obtained from Pfaltz & Bauer and also used as received. Tri-n-butyltin hydride (Alfa Division, Ventron Corp.) was vacuum distilled and stored under argon before use. The free radical initiator azobis(isobutyronitrile) (AIBN) used in the reduction was also purchased from Alfa Division. The 2,4,6-trichloroheptane was obtained from a new synthesis which involves the hydrohalogenation of 1,6heptene-4-diol and the chlorination of the resulting alcohol. A detailed description of this method can be found elsewhere (11). S A M P L E P R E P A R A T I O N . In a small vial 22.5 mg of A I B N was mixed with 1.7 ml of perdeuterobenzene and the mixture held at 0 C to permit dissolution of the A I B N . The chloroalkane and 0.2 ml of the N M R reference material hexamethyldisiloxane (HMDS) were placed in a 10 mm N M R tube. The AIBN/benzene solution was added to the N M R tube and placed under an argon atmosphere in a glove bag. The freshly distilled (n-Bu) SnH (1.0-1.7 ml) was transferred by syringe into the solution. Following a thoroug argon for several minute chlorinated alkane varied between 0.2 and 0.4 ml (7.0-12.5% v / v ) and the (n-Bu) SnH added was equal to the molar concentration of chlorine atoms present. The sample was placed in the N M R spectrometer at 50 ° C and the C N M R spectra were recorded as the reduction proceeded. 0

3

3

1 3

M E A S U R E M E N T S . Initially, the reduction of 2-chloro-4methylpentane was carried out in order to ascertain the ideal temperature which would lead to complete reduction in about six hours. The progress of this reduction was followed by Ή N M R , recording a single scan every thirty minutes. It was found that at 5 0 C the reaction reaches 80% of completion after 5 hr. A l l subsequent reductions were carried out at this temperature. The 50.31 M H z C N M R spectra of the chlorinated alkanes were recorded on a Varian XL-200 N M R spectrometer. The temperature for all measurements was 5 0 C . It was necessary to record 10 scans at each sampling point as the reduction proceeded. A delay of 30 s was employed between each scan. In order to verify the quantitative nature of the N M R data, carbon-13 Tj data were recorded for all materials using the standard 1 8 0 ° - r - 9 0 ° inversion-recovery sequence. Relaxation data were obtained on (n-Bu) SnH, (n-Bu) SnCl, D C P , T C H , pentane, and heptane under the same solvent and temperature conditions used in the reduction experiments. In addition, relaxation measurements were carried out on partially reduced (70%) samples of D C P and T C H in order to obtain T data on 2-chloropentane, 2,4-dichloroheptane, 2,6-dichloroheptane, 4chloroheptane, and 2-chloroheptane. The results of these measurements are presented in Table II. In the N M R analysis of the chloroalkane reductions, we measured the intensity of carbon nuclei with T values such that a delay time of 30 s represents at least 3 T . The only exception to this is heptane where the shortest T is 12.3 s (delay = 2.5Tj). However, the error generated would be less than 10%, and, in addition, heptane concentration can also be obtained by product difference measurements in the T C H reduction. Measurements of the nuclear Overhauser enhancement (NOE) for carbon nuclei in the model compounds indicate uniform and full enhancements for those nuclei used in the quantitative measurements. Table II also contains the chemical N M R

0

13

0

3

3

x

t

2

t

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26.

JAMEISON ET AL.

Reduction of Poly (vinyl chloride)

361

Table Π C NMR Spin Lattice Relaxation Times ( Τ ) and Chemical Shifts (6) }

6

H-Sn4C-C-C-C),

Cl-SnfC-C-C-C), CI I

m,r

6.0 8.5 7.3 8.1

a 17.53 b 27.04 c 28.19

4.5 7.0 5.9

CI

24.49 55.38 54.24 50.86 50.51

ι

c-c-c-c-c a b c

CI

T, (s)

8.30 27.41 30.24 13.82

a b c d

(r) (m)

M (m) (r) (m)

6.4 15.7 15.8 8.9 8.8

c-c-c-c-c

a b c d e

25.41 57.58 42.82 20.06 13.56

9.0 21.8 13.3 14.8

C-C-C-C-C

a 14.12 b 22.62 c 34.46

10.8 24.6 24.4

a

b

c

d

e

25.34 a 24.21 24.11

,

CI I

m,r

CI CI ι m,r |

c-c-c-c-c-c-c a

b

e

d

C

/") m

r

3.5— 3.7

/ \ (mm) r

m

55.19 55.07 w. 54.14 53.93

(rr) (rnr) (rm) (mm)

8.1—8.4

49.02 48.84 48.33 47.81

(«) (mr) (rm) (mm)

4.4-* 4.6

58.32

(rr) (mr) (rm) (mm)

v4

d 57.44 56.39

8.2 8.1 8.0

Continued on next page

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

362

CHEMICAL REACTIONS ON POLYMERS

Table U (continued)

is C NMR Spin Lattice Relaxation Times (Tj) and Chemical Shifts (6)

25.59 23.50 , 55.56 54.41 49.30 a

_ , Cl

Cl

59.58 41.10 40.07 19.76 19.61

(r) (m) (r)

g 14.07

W (m)

m e

f

m, r

ι

b

I C - C - C - C - C - C - C a

b

c

(r)

.

Γ

I

(m)

c

I · I C - C - C - C - C - C - C a b c d β f g m

(r) (m) (r)

d

c

d d

Q| I

•c-c-c-c-c-c

(m)

25.33

(r)

25.30

(m)

·80

(r) M

57

U

(m)

Ο

t

.OU

40.07 40.02 2

4

1

0

24.02

.

(r) (m)

W

(m)

12.4

-5.7 -11.0 y.

6.4

- 36 3

6

a 14.07 b 19.96 c 41.01

12.4 8.9 6.3

a 25.40 b 58.25 c 40.71 d 26.60 e 31.64 f 22.80 g 14.20

5.7 14.6 7.2 8.5 9.3 10.5 12.3

a 14.20 b 23.01

12.3 13.2 12.3 12.4

b e d

Q| I

C - C - C - C - C - C - C a b c d e f g

C - C - C - C - C - C - C a b c d

c 32.24 d 29.35

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26.

JAMEISON ET AL.

Reduction of Polyfvinyl chloride)

363

shift data for all compounds studied. The chemical shift data for the T C H sample agrees well with that of an earlier report where the shift assignment of each stereoisomer was established (12). The percent reduction was determined by comparing the amounts of (n-Bu) SnH and (n-Bu) SnCl at each measurement point. 3

3

K I N E T I C S O F (n-BU) SnH R E D U C T I O N O F D C P A N D 3

TCH.

DCP R E D U C T I O N . As illustrated below D C P (D) is sequentially transformed into 2-chloropentane (M) and then to pentane (P) during its reduction with (n-Bu) SnH. 3

D — > Μ —>

The ratio of rate constants K=(k /k ) concentrations of D an according to

Ρ

can be obtained (13) from the

(D

κ-ι

where the subscripts ο and χ indicate concentrations initially and after % reduction x. A n alternative means to determine the relative rates of reduction of M and D, ie. Κ = k /k , is afforded by comparing the simultaneous (nBu) SnH reductions of D C P and 2-chlorooctane (Μ') to pentane and octane (O), respectively. M

D

3

kn D —>

7

In this case K = W*x>

i s

•> Ρ

M

S'iven by (13)

In

M' 0

(2)

ln

Equation (2) can also be used to determine the relative rates of reduction of meso (m) and racemic (r) D C P (D , D ) where M' and D are replaced by D and D . m

m

r

r

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

364

! ^

D r

>

M

h L

>

P

T C H R E D U C T I O N . In the early stages of the reduction of T C H (T) with (n-Bu) SnH it is possible to compare the relative reactivities of the central (4) and terminal (2,6) chlorines. A t these levels of reduction only 2,6 and 2,4-dichloroheptanes (2,6-D and 2,4-D) are produced, as shown below. 3

κ

Ε

Τ —>

2,4-D

We can establish the relative reactivities, k /k , of the central (C) and terminal (E) chlorines directly from the relative concentrations of the resulting dichloroheptanes. c

k

c

E

2,6-£

=

k

2,4-D

E

(

3

)

R E S U L T S A N D DISCUSSION K I N E T I C R E S U L T S F O R D C P A N D T C H . The portion of the 50.13 M H z C N M R spectra containing the methylene and methine carbon resonances of D C P and the resultant products of its (n-Bu) SnH reduction are presented in Figure 2 at several degrees of reduction. Comparison of the intensities of resonances possessing similar T i relaxation times (see above) permits a quantitative accounting of the amounts of each species (D,M,P) present at any degree of reduction. In Figure 3 the percentages of D (DCP), M (2-chloropentane), and Ρ (pentane) observed during the (n-Bu) SnH reduction of D C P are plotted against the degree of reduction x. Equation (1) is solved for K = k / k by least-squares fitting the calculated and observed values of the ratio (M /D ). The observed ratios (p /D ) are substituted into E q . 1 to obtain the calculated ratios (M /D ) corresponding to the assumed Κ = k /k and these are compared with the observed ratios (M /D ). This procedure yields Κ = k /k = 0.26, which means that D C P is ~ 4 times more easily reduced than 2-chloropentane. Comparison of the simultaneous reduction of D C P and 2-chlorooctane gave according to Equation (2) K = k >/k = 0.24, lending further support to the observation that chlorines belonging to a W diad are removed 4 times faster than an isolated chlorine in say an E V E triad. Furthermore, the observed rates of (n-Bu) SnH reductions of 2- and 4-chlorooctanes were 1 3

3

3

M

x

x

x

x

M

D

0

x

x

M

x

D

7

M

D

3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

z >

26. J A M E I S O N E T A L .

Reduction of Polyfvinyl chloride)

CZ

I

CH

3

CZ

m,r

— CH

I

365

—

2

CH

2

I —

CH

—

CH

3

3

CZ

I

28% CH

3

—

I

CH — 2

CH

2

— C H

— C H

2

3

3

M-3 M-2

60%

CH

3

— C H

I

55

'

45

ppm vs

'

2

2

— C H

2

— C H

2

—

CH

3

3

35

TMS

13

Figure 2. 50.31 M H z C N M R spectra of D C P (D) and its products (M and P) resulting from 0, 28, 60, and 81% reduction with (n-Bu) SnH. 3

X,

%

REDUCTION

Figure 3. Distribution of reactants (D, M ) and products (M, P) observed in the (n-Bu) SnH reduction of D C P . D = D C P , M = 2chloropentane and Ρ = pentane (see Figure 2). 3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

366

CHEMICAL REACTIONS ON POLYMERS

identical within experimental error. This means that the reactivity of an isolated chlorine is independent of structural position or chain end effects. The observed ratio of m to r isomers, m /r remaining during the (n-Bu) SnH reduction of D C P (see Figure 2) are plotted in Figure 4. ratio of k /k = 1.3. Substituting Apparently m - W diads are 30% more reactive toward (n-Bu) SnH than are r - W diads. Our C N M R analysis (2) of the E - V copolymers obtained via the (n-Bu) SnH reduction of P V C led to k / k = 1 . 3 1 ±0.1 in excellent agreement with the kinetics observed for the removal of chlorines from m- and r - D C P . We also found no W diads in those E - V copolymers made by removing more than 80% of the chlorines from P V C . This observation is confirmed in the (n-Bu) SnH reduction of D C P where the chlorines in this P V C diad model compound were found to be 4 times easier to remove than the isolated chlorines in 2-chloropentane, 2-, and 4-chlorooctane. The C N M R spectr (n-Bu) SnH are shown i ngure and those listed in Table II were obtaind by comparison to the chemical shift data of T C H , D C P , 2-, and 4-chlorooctanes. From the relative concentrations of 2,6- and 2,4-dichloroheptane (2,6-D and 2,4-D) observed in the early stages of T C H reduction with (n-Bu) SnH we determine according to Equation (3) that the reactivity of the central chlorine in T C H is 50% greater than the terminal chlorines, ie. k /k =1.5. We also find the reactivity of the central chlorine in T C H to depend on its stereoisomeric environment as follows: mm>mr or rm>rr. In Figure 6 we have plotted and compare the triad sequences observed in the reduction of T C H and P V C with (n-Bu) SnH. The curves numbered 0,1,2, and 3 correspond to triads containing 0 (EEE), 1 ( V E E + E E V + E V E ) , 2 ( W E + E W + V E V ) , and 3 Î V W ) chlorine atoms. There is agreement between the curves describing the products of reduction for T C H and P V C providing strong support for considering T C H an appropriate model compound for the (n-Bu) SnH reduction of P V C . This clearly implies that the (n-Bu) SnH reduction of P V C is independent of comonomer sequences longer than triads. The first column of Table III lists all possible C NMR distinguishable E - V triads whose central units are V . In the next column we present the same triad structures in binary notation (0=E, 1=V) with the central unit labeled as the site of (n-Bu) SnH attack and the terminal units as either — (preceeding site) or + (following site). The final column presents the relative reactivities of the central V ( l ) unit in each triad toward (n-Bu) SnH based on the kinetics of reduction determined for D C P and T C H . For the E W (Oil) triads, removal of the central chlorine atoms is expected to be 3.5 (r) and 4.6 (m) times faster than for the isolated chlorine atom in the E V E (010) triad, because k /k = 4.0 and k /k = 1.3 for D C P . The central chlorines in V W (111) triads are 6.0 (mr or rm), 4.6 (rr), and 7.8 (mm) times more reactive toward (n-Bu) SnH than the chlorine in the E V E triad based on k /k = 4.0 and k J/k = 1.3 x

XJ

3

Dm

Df

3

1 3

3

m

r

3

1 3

3

3

c

E

3

3

3

1 3

3

3

D

M

Dn

3

D

for D C P and k /k c

E

M

D

= 1.5 for T C H .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Df

Df

26.

JAMEISON ET AL.

Reduction of Poly (vinyl chloride)

367

Figure 4. Ratio of the relative amounts of m and r isomers of D C P remaining after reduction by (n-Bu) SnH,as measured by the carbon-13 methylene (see Figure 2) and methyl resonances. 3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

64

0%

62

—i

1 58

ppm

1

I 56

VS T M S

ι

ι

I 54

mm

•

mr

I

52

I

3

2

I —CH

CJl

CH

3

3

13

3

— CH

3

— CH2— CH 2

3

2

1

CH

I

2

2

2

2

5

2

4

5

— C H — CH

4

— CH — C H

I

C£

4

4

— CH — CH

m, r

4

2

2

2

2

2

—CH — CH

m,r — CH — C H — CH — C H

3

2

2

m, r

CH

3

— CH — C H

I

CJL

3

—CH — C H 2

I

2

3

3

m, r

1

CH

1

CH

I

est

6

2

—CH

7

7

— CH — CH

2

2

CH —CH 6

— CH

—

—CH — CH

3

3

3

3

3

— CH — C H

I

Figure 5. Methine carbon region of the 50.31 M H z C N M R spectra of T C H at 0 and 43% reduction with (n-Bu) SnH.

1 60

rr

rr

rm

H-2

»

en

*


»w

>

ο

w

η

oo

26.

JAMEISON ET AL.

Reduction of Poly (vinyl chloride)

369

X, % R E D U C T I O N 1 3

Figure 6. Comonomer triad distributions observed by C N M R analysis during the (n-Bu) SnH reductions of T C H ( ) and P V C ( ). 3

Table ΠΙ Relative Reactivities of the Central Chlorines in E-V Triads

E-V Triad

-

reduction site

+

k (relative)

EEE

0

0

0

0.0

EVE

0

1

0

1.0

1

3.5

1

4.6

EW

0

EW

0

VW

1

WV

1

VW

1

1 1

r m

m -

Γ

j

r

Γ

m -

1

4.0 X 1.5 = 6.0

1

6.0 -r 1.3 = 4.6

m 1

6.0 X 1.3 = 7.8

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

370

CHEMICAL REACTIONS ON POLYMERS

C O M P U T E R SIMULATION OF T C H AND P V C

REDUCTION.

We begin with 100 T C H molecules reflecting the stereochemical composition of our unreduced T C H sample, ie. 52 (mr or rm), 28 (rr), and 20(mm) stereoisomers. A T C H molecule is selected by generating a random integer, I , where I < 101. If I < 53, then the T C H molecule chosen is a mr or rm isomer. If 52 < I < 81, then the T C H is rr, and if I > 80 the T C H selected is a mm isomer. Next we randomly choose either one or the other terminal units or the central unit of our selected T C H isomer and check to see if it is a V ( l ) unit or an E(0) unit. If a terminal V unit is chosen we check to see if the neighboring central unit is V or E. If the central unit is also V, then we determine whether this W diad is m or r. For r and m W diads the relative reactivities of the terminal V unit chlorine are 3.5 and 4.6, respectively (see Table III). If the central unit is E, then we assume the relative reactivity of the isolated terminal units in the V E E or V E V triads to be identical to the isolated central unit in the E V E triads. This assumption is supported b observed here for the 2 random number between reactivity divided by the sum of the relative reactivities of all chlorines in the V W , EW or W E , VEV, V E E or EEV, and E V E isomers of T C H and partially reduced T C H (see Table III), then we remove the terminal chlorine (1—K)) and modify the relative reactivity of the central V unit in the selected T C H isomer, because its terminal neighbor has been changed from V to E. This procedure is repeated until the desired per cent reduction, x, is reached, where χ = 100 X (# of chlorines removed 300). Each of the 100 T C H molecules is then tested for the number and sequence of V units remaining at this current value of x. In Figure 7 we plot the per cent of T C H molecules containing 3, 2, 1, and 0 chlorines, or V units, determined from our simulation and compare them to the values observed for T C H at various degrees of (n-Bu) SnH reduction. Agreement between the simulated and observed reduction products of T C H based on the kinetics observed for both D C P and T C H is good. Simulation of the (n-Bu) SnH reduction of P V C is carried out in a manner similar to that described for T C H . Instead of beginning with 100 T C H molecules we take a 1000 repeat unit P V C chain that has been Monte Carlo generated to reproduce the stereosequence composition of the experimental sample of P V C used in the reduction to E-V copolymers (2), ie. a Bernoullian P V C with P =0.45. A t this point we have generated a P V C chain with a chain length and a stereochemical structure that matches our experimental starting sample of PVC. We select repeat units at random, and if they are unreduced V units a check of whether or not the units adjacent to the selected unit are Ε or V is made. Having determined the triad structure (both comonomer and stereosequence) of the repeat unit selected for reduction, we divide the relative reactivity of this E-V triad by the sum of relative reactivities for all V centered E-V triads as listed in Table III to obtain the probability of reduction. A random number between 0.0 and 1.0 is generated, and if it is smaller than the probability of reduction of the selected E-V triad, we remove the chlorine from the central V unit which becomes an Ε unit. If either of the terminal units of the E-V triad selected are V units, then we modify their relative reactivities to reflect changing the central unit from V to E. The degree of reduction χ is calculated from 100 X (# r

r

r

r

r

3

3

m

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26.

JAMEISON ET AL.

371

Reduction of Poly(vinyl chloride)

of chlorines removed -f 1000), and if it corresponds to the desired level of reduction we print out the numbers of each type of triad remaining in the E - V copolymer. This whole procedure is repeated for several P V C chains until the fraction of each E - V triad type at each degree of reduction remains constant when averaged over the generated set of chains. Figure 8 presents a comparison of observed (see Table I) and simulated E - V triad composition plotted against the degree of overall reduction by (n-Bu) SnH. The agreement is excellent being much improved over that found for T C H reduction. This is at least partially a consequence of the relative accuracy of the C N M R data used to obtain the E - V triad compositions resulting from the reduction of P V C , because the T C H data is gathered during reduction and is an average over the time required to accumulate C N M R spectra (~ 10 min.), while E - V data is obtained on static samples removed from the reduction flask. In Figure 9 we have plotted the ratios of r / m W diads observed by C N M R in E - V copolymers obtained by the (n-Bu) SnH reduction of P V C (2). They are compare computer simulation of P V of the kinetics of (n-Bu) SnH reduction of D C P and T C H . The agreement is good, and provides us with a knowledge of E - V stereosequence as a function of comonomer composition. The excellent agreement between the simulated and observed reduction of P V C with (n-Bu) SnH means that both D C P and T C H are appropriate model compounds for the study of P V C reduction. D C P is useful to obtain kinetic information on the relative reactivities of m- and r-diads and W and E V diads. Reduction of T C H yields the relative reactivities of the central and terminal chlorines in the V W triads. The physical properties (7-10) of our E - V copolymers are sensitive to their microstructures. Both solution (Kerr effect or electrical birefringence) and solid-state (crystallinity, glass-transitions, blend compatibility, etc.) properties depend on the detailed microstructures of E - V copolymers, such as comonomer and stereosequence distribution. C N M R analysis (2) of E - V copolymers yields microstructural information up to and including the comonomer triad level. However, properties such as crystallinity depend on E - V microstructure on a scale larger than comonomer triads. For example, the amount and stability of the crystals formed in E - V copolymers depend on the number and length of uninterrupted, all Ε unit runs. Our ability to computer-simulate the (n-Bu) SnH reduction of P V C permits us to obtain this information concerning the longer comonomer sequences in the resultant E - V copolymers. In Figure 10 we present the percentage of Ε units that are found in uninterrupted, all Ε unit runs as a function of the length of each run and the over all degree of reduction. These data were obtained in two ways: i.) simulation of the (n-Bu) SnH reduction of P V C and ii.) assuming random removal of CI during the reduction. The simulated data in Figure 10 make clear that the numbers and lengths of all Ε unit runs in E - V copolymers obtained from the reduction of P V C with (n-bu) SnH are significantly reduced compared to those resulting from random CI removal. Though not shown in Figure 10, the percentage of Ε units in all Ε unit runs . . . V E , V . . . with χ > 29 is 27 % for random CI removal and just 14 % for the (n-Bu) SnH reduced P V C . This observation has to be considered when discussing the crystalline 3

13

13

13

3

3

13

3

3

3

3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

372

X,%

REDUCTION

Figure 7. A comparison of the observed (symbols) and simulated (solid lines) comonomer triad distributions in (n-Bu) SnH reduced T C H . 3

PVC

X,% R E D U C T I O N

Figure 8. A comparison of the observed (symbols) and simulated (solid lines) comonomer triad distributions in (n-Bu) SnH reduced P V C . 3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26.

Reduction of Poly (vinyl chloride)

JAMEISON ET AL.

373

4.0h

3.0

2.0

40

20

60

80

X, % R E D U C T I O N

Figure 9. A comparison of the observed (O) and simulated ratios of r / m W diads during the (n-Bu) SnH reduction of P V C . 3

15

\ 70% REDUCTION /\\ -Γ

\

;

^ V.

\

Λ

; 90% \ \ Λ REDUCTION V I

Λη

/ \ / !- \f

A

\

\

A

/\

/ v

/ \

0

2

ι

4

I 6

1 8

T^-4>C^J»' 10 12 14

V

ι\ / ι Ν ί ι Ν 16 18 2 0 22 24 26 28

X(...VE V...) X

Figure 10. Percentage of Ε units in uninterrupted, all Ε unit runs as a function of run length and degree of reduction. Solid lines correspond to the computer simulation of P V C reduction with (n-Bu) SnH and the dotted lines to the simulated results assuming random CI removal. 3

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

374

CHEMICAL REACTIONS O N POLYMERS

morphology of E - V copolymers obtained by reduction of PVC with (n-Bu) SnH. With the (n-Bu) SnH reduction of PVC successfully simulated via the kinetic studies of DCP and T C H reduction, it remains to explain the mechanisms (14) of this reductive dechlorination. We need only consider the mechanisms of the reduction of DCP and T C H , because we have demonstrated that the kinetics of their reduction are the same as those observed for PVC when also reduced by (n-Bu) SnH. 3

3

3

POSSIBLE M E C H A N I S M F O R T H E R E D U C T I O N O F P V C W I T H (n-BU} SnH. The reductions of alkyl halides with (n-Bu) SnH are known (15) to be free-radical chain reactions, where the (n-BuJ Sn* radical (R») abstracts the halogen (X) from the alkyl halide (ROC) creating an alkyl radical (R'*) and (n-Bu) SnX. In Figure 11 (a,b) the rr and mm isomers of T C H are depicted in their most probable conformations (tttt and gtgi) (16), with their central CPs about to be abstracted by the R». Attack at the central chlorine by R« is hindered (14) by both adjacent methin while only a single methin central chlorine in the gtgt conformer of mm-TCH. We would expect, as is observed, the mm isomer to be more readily reduced than the rr isomer based solely on considerations of steric interactions. 3

3

3

3

rr ( t t t t )

(a)

CH

(b)

,CH

3

3

mm

(gtgt)

t Figure 11. (a,b)-The rr and mm isomers of T C H in the tttt and gtgt conformations.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

26.

Reduction of Poly (vinyl chloride)

JAMEISON ET AL.

375

Since the (n-Bu) Sn* radical (R#) is nucleophilic (17), a partial negative charge must be produced at the methine carbon whose chlorine is being abstracted. The rate of this abstraction should clearly be enhanced by electron-withdrawing groups on R'« due to their stabilization of this charge by inductive effects. As observed, the removal of CI from E W (or W diad) is expected to be more facile than from E V E (or V E diad) as a result of a 7-halogen effect in the former structure. Thus, the enhancements in chlorine removal from W diads compared to E V diads and from m - W diads compared to r - W diads observed in the (n-Bu) SnH reduction of D C P , T C H , and P V C are consistent with the free-radical chain reaction mechanism. Inductive effects produced by neighboring 7-Cl's tend to favor the reduction of W diads relative to E V diads and steric interactions resulting from different preferred conformations in each isomer favor the removal of CI from mW diads relative to r - W diads. 3

3

LITERATURE CITED

1. Starnes Jr., W. H.; Schilling, F. C.; Plitz, I. M.; Cais, R. E.; Freed, D. J.; Hartless, R. L.; Bovey, F. A. Macromolecules 1983, 16, 790, and references cited therein. 2. Schilling, F. C.; Tonelli, A. E.; Valenciano, M. Macromolecules 1985 , 18, 356. 3. Keller, F.; Mugge, C. Faserforsch. Textiltech. 1976, 27, 347. 4. Misono, Α.; Vehida, Y.; Yamada, K. J. Polym. Sci., Part Β 1967, 5, 401, and Bull. Chem. Soc. Jpn. 1967, 40, 2366. 5. Misono, Α.; Uchida, Y.; Yamada, K.; Saeki, T. Bull. Chem. Soc. Jpn. 1968, 41, 2995. 6. Hagiwara, M.; Miura, T.; Kagiya, T. J. Polym. Sci., PartA-11969, 7, 513. 7. Tonelli, A. E.; Schilling, F. C.; Bowmer, T. N.; Valenciano, M. Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem. 1983, 24 (2), 211; and Tonelli, A. E.; Valenciano, M.; Macromolecules 1986, 19, 2643. 8. Bowmer, T. N.; Tonelli, A. E. Polymer 1985, 26, 1195. 9. Bowmer, T. N.; Tonelli, A. E. Macromolecules 1986, 19, 498. 10. Bowmer, T. N.; Tonelli, A. E. J. Polym. Sci., Polym. Phys. Ed. 1986, 24, 1631; and ibid 1987, 25, 1153. 11. Schilling, F. C.; Schilling, M. L. Macromolecules Submitted. 12. Tonelli, A. E.; Schillling, F. C.; Starnes, Jr., W. H.; Shepherd, L.; Plitz, I. M. Macromolecules 1979, 12, 78. 13. Benson, S. W. "The Foundations of Chemical Kinetics"; McGraw­ -Hill:New York, 1960. 14. Starnes Jr., W. H.; Schilling, F. C.; Abbas, Κ. B.; Plitz, I. M.; Hartless, R. L.; Bovey, F. A. Macromolecules 1979, 12, 13. 15. Carlsson, D. J.; Ingold, K. U. J. Am. Chem. Soc., 1968, 90, 7047. 16. Flory, P. J.; Pickles Jr., C. J. J. Chem. Soc., Faraday Trans. 1973, 69, 2. 17. Grady, G. L.; Danyliw, T. J.; Rabideux, P. J. Organomet. Chem. 1977, 142, 67. RECEIVED September 23, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 27

Identification of Products from Polyolefin Oxidation by Derivatization Reactions 1

D. J. Carlsson, R. Brousseau, Can Zhang , and D. M. Wiles Division of Chemistry, National Research Council of Canada, Ottawa K1A 0R9, Canada A series of reaction for the rapid quantification of many of the major products from the oxidation of polyolefins. Infrared spectroscopy is used to measure absorptions after gas treatments. The gases used and the groups quantified include phosgene to convert alcohols and hydroperoxides to chloroformates, diazomethane to convert acids and peracids to their respective methyl esters, sulfur tetrafluoride to convert acids to acid fluorides and nitric oxide to convert alcohols and hydroperoxides to nitrites and nitrates respectively. In some cases it is possible to differentiate between the various alkyl substituents. Primary, secondary and tertiary nitrates and nitrites all show clearly diffe­ rent infrared absorptions. The spectra of acid fluo­ rides can be used to differentiate chain-end groups from pendant acid groups. Furthermore, the loss of all -OH species upon sulfur tetrafluoride exposure allows the reliable estimation of ketones, esters and lactones without the complication of hydrogen-bon­ ding induced shifts in the spectra. Preliminary re­ sults from the use of these reactions to characterize γ-ray oxidized polyethylene and polypropylene are used to illustrate the scope of the methods. H y d r o c a r b o n s o x i d i z e to g i v e a complex m i x t u r e of p r o d u c t s w h i c h i n ­ clude h y d r o p e r o x i d e s , alcohols, ketones, acids, esters, etc. (1). P o l y o l e f i n s s i m i l a r l y c a n be o x i d i z e d b y h e a t , r a d i a t i o n o r m e c h a n o initiated processes. T h e p r e c i s e i d e n t i f i c a t i o n a n d q u a n t i f i c a t i o n of t h e s e o x i d a t i o n p r o d u c t s a r e e s s e n t i a l f o r t h e complete u n d e r s t a n ­ d i n g a n d c o n t r o l of t h e s e d e s t r u c t i v e reactions. Conventional m e t h o d s f o r t h e i d e n t i f i c a t i o n of o x i d a t i o n p r o d u c t s i n c l u d e i o d o m e N O T E : This chapter was issued as N R C C No. 27914. 1

Guest research scientist from Academia Sinica, Institute of Chemistry, Beijing, China 0097-6156/88/0364-0376506.00/0 Published 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

27.

CARLSSON ET AL.

377

Products from Polyoiefin Oxidation

try a n d i n f r a r e d (IR) s p e c t r o s c o p y (2-4). Iodometry sums a l l h y d r o p e r o x i d e s a n d p e r a c i d s , b u t also may i n c l u d e some d i a l k y l p e r ­ oxides. IR c a n n o t d i f f e r e n t i a t e b e t w e e n h y d r o g e n - b o n d e d a l c o h o l and h y d r o p e r o x i d e - O H groups and is only paritally successful i n t h e r e s o l u t i o n of t h e mix of c a r b o n y l s p e c i e s f o r m e d . In c o n t r a s t , l i q u i d p h a s e , n u c l e a r m a g n e t i c r e s o n a n c e ( n . m . r . ) has t h e r e s o l u ­ t i o n to p o t e n t i a l l y d i f f e r e n t i a t e a l l of t h e s e p r o d u c t s ( 5 , 6 ) . This m e t h o d i s limited i n t h r e e a r e a s ; low s e n s i t i v i t y (as c o m p a r e d to IR f o r e x a m p l e ) , l o n g d a t a a c q u i s i t i o n times a n d t h e n e e d to d i s s o l v e the samples. T h e n e c e s s i t y for p r o l o n g e d h i g h t e m p e r a t u r e s to a c h i e v e s o l u t i o n makes q u e s t i o n a b l e t h e f i n a l a n a l y s e s b e c a u s e of t h e t h e r m a l i n s t a b i l i t y of s e v e r a l o f t h e k e y p o l y m e r o x i d a t i o n p r o d u c t s . Derivitization reactions have previously been employed to e x t e n d the s e n s i t i v i t y a n d r e s o l u t i o n of I R , u l t r a v i o l e t a n d X - r a y photo-electron spectroscopy (7-13). Y e t no p r o p o s e d method has t h e r a n g e to accommodat fins. A s p a r t of an o n g o i n z a t i o n , we d i s c u s s h e r e ga molecules. T h e p r o d u c t s from t h e s e r e a c t i o n s c a n b e r a p i d l y i d e n t i ­ fied and quantified b y I R . Some of t h e s e r e a c t i o n s a r e n e w , o t h e r s have already been d e s c r i b e d i n the l i t e r a t u r e , although t h e i r p r o ­ d u c t s h a v e not a l w a y s b e e n f u l l y i d e n t i f i e d . Experimental A d d i t i v e - f r e e film samples of i s o t a c t i c p o l y p r o p y l e n e ( i P P , 30pm Himont P r o f ax r e s i n ) a n d p o l y e t h y l e n e s ( L L D P E , 120pm, l i n e a r low d e n s i t y D u P o n t S c l a i r r e s i n , a n d U H M W - P E , 120pm, u l t r a h i g h m o l e ­ c u l a r w e i g h t , h i g h d e n s i t y Himont L S R 5641-1B r e s i n ) were o x i d i z e d by exposure i n a i r to γ - r a d i a t i o n ( A E C L Gamma C e l l 220, 1.0 Mrad/h). Films were s t o r e d at - 2 0 ° u n t i l a n a l y s i s c o u l d be c a r r i e d out. O x i d i z e d films a n d d e r i v a t i z e d , o x i d i z e d films were c h a r a c ­ t e r i z e d b y i o d o m e t r y ( r e f l u x with N a l i n i s o p r o p a n o l / a c e t i c a c i d ) a n d b y t r a n s m i s s i o n F o u r i e r T r a n s f o r m ( F T ) IR ( P e r k i n E l m e r 1500), u s i n g t h e s p e c t r a l s u b t r a c t i o n t e c h n i q u e ( 3 , 14). F r e e r a d i c a l s were m e a s u r e d b y the e l e c t r o n s p i n r e s o n a n c e t e c h n i q u e ( e . s . r . , V a r i a n E4 s p e c t r o m e t e r ) . Films were e x p o s e d to e a c h r e a c t i v e gas at room t e m p e r a t u r e i n a simple flow s y s t e m w h i c h c o u l d be sealed o f f b y v a l v e s to allow r e a c t i o n to p r o c e e d . A f t e r r e a c t i o n , t h e v a r i o u s g a s e s were s w e p t out with N b e f o r e film a n a l y s i s . T h e g a s e s u s e d i n c l u d e d SF^ , S 0 , COCl a n d N O ( M a t h e s o n , u s e d as s u p p l i e d ) . T h e e x c e p t i o n was CH N w h i c h was g e n e r a t e d as r e q u i r e d i n s m a l l amounts a d j a c e n t to t h e films b y t h e r e a c t i o n of e t h a n o l i c K O H o n D i a z a l d ( A l d r i c h ) i n t h e r e a c t o r d e s c r i b e d b y F a l e s et al (15). The C H N r e a c t i o n s were p e r f o r m e d with films at 2 2 ° C a n d also at - 7 8 ° C , b u t t h e the C H N r e a g e n t s at ~ 2 0 ° C i n b o t h c a s e s . To prevent N 0 f o r m a t i o n from NO-0 r e a c t i o n , films were s w e p t with N f o r a b o u t 5 m i n u t e s p r i o r to N O i n t r o d u c t i o n . Because SF attacks g l a s s , these reactions were c a r r i e d out i n an a l l - p o l y e t h y l e n e flow s y s t e m with Monel v a l v e s . F r o m t h e F T I R c h a n g e s , a l l gas r e a c t i o n s were v i r t u a l l y complete i n ~ 15 h f o r t h e t h i n i P P films a n d ~ 24 h f o r t h e L L D P E . 2

2

2

2

2

2

2

2

2

2

2

l+

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

2

CHEMICAL REACTIONS ON POLYMERS

378

F o r c o m p a r i s o n p u r p o s e s , some m o d e l c o m p o u n d s a n d m o d e l p o l y m e r s were r e a c t e d with the g a s e s . L i q u i d models were u s e d as d i l u t e s o l u t i o n s i n h e x a n e o r h e x a d e c a n e ; m o d e l p o l y m e r s were u s e d as s o l i d f i l m s . n - P e r o c t a n o i c a c i d was sunthesised from n - o c t a n o i c acid

w i t h 30% h y d r o g e n p e r o x i d e

(-C^

I R a b s o r p t i o n s at 1755

cm" in hexane solution)(16). Tert.-buty?Siydroperoxide (99%) was p u r i f i e d b y the a z e o t r o p i c d i s t i l l a t i o n of t h e c o m m e r c i a l 70% hydroperoxide/water mixture ( A l d r i c h ) . n-Octanoic acid, 2-ethylhexanoic acid, stearic a c i d , γ - d e c a l a c t o n e , 1,1,3,3-tetramethylbutane 1-hydrop e r o x i d e ( L u c i d o l ) were u s e d as s u p p l i e d . P o l y m e r s u s e d to i d e n ­ t i f y gas r e a c t i o n s i n c l u d e d p o l y ( m e t h y l m e t h a c r y l a t e ) , a p r o p y l e n e / a c r y l i c acid c o p o l y m e r , poly ( v i n y l alcohol) ( Poly sciences ), P h e n o x y ( U n i o n C a r b i d e , p o l y m e r of t h e 2 - h y d r o x y p r o p y l e t h e r of b i s p h e n o l A ) a n d an e t h y l e n e / c a r b o n m o n o x i d e c o p o l y m e r . 1

Results and Discussion The γ - i n i t i a t e d oxidatio i s l e s s complex t h a n t h a t r e s u l t i n g from p h o t o - o r t h e r m a l l y i n i t i a t e d degradation. T h i s r e s u l t s from the mild c o n d i t i o n s i n the γ - c e l l , w h e r e the major i n i t i a l o x i d a t i o n p r o d u c t , t h e - O O H g r o u p , i s s t a b l e . A l t h o u g h the d e r i v a t i z a t i o n methods a r e a p p l i c a b l e to a l l t y p e s of o x i d a t i o n , f o r s i m p l i c i t y o n l y the γ - i r r a d i a t e d s y s t e m s will b e c o n ­ sidered here. T h e γ - i n i t i a t e d o x i d a t i o n of i P P a n d L L D P E p r o d u c e s IR s p e c ­ t r a l c h a n g e s i n the ~ 3400 c m " , ~ 1715 cm" a n d ~ 1170 cm" r e g i o n s ( F i g s . 1 and 2). T h e s e r e g i o n s a r e b r o a d l y a t t r i b u t e d to h y d r o g e n b o n d e d alcohol a n d / o r h y d r o p e r o x i d e , c a r b o n y l and - C - 0 - ? a b s o r p ­ tions, respectively. 1

1

1

I n i t i a l l y , v a r i o u s l i q u i d p h a s e r e a g e n t s were e x p l o r e d f o r t h e i d e n t i f i c a t i o n of t h e d i f f e r i n g - O H s p e c i e s a n d c a r b o n y l s p e c i e s i n the solid films. T h e s e r e a g e n t s i n c l u d e d e t h a n o l i c sodium h y d r o x i d e [to generate IR-detectable c a r b o x y l a t e g r o u p s from a c i d s (10)], a n d benzidine [ f o r the c o l o r i m e t r i c d e t e r m i n a t i o n of p e r a c i d s (17 ) ] . H o w e v e r , r e s u l t s were d i s a p p o i n t i n g with little r e a c t i o n o b s e r v e d . T h i s may h a v e r e s u l t e d e i t h e r from l a c k of p e n e t r a t i o n of t h e r e ­ a g e n t s i n t o the p o l y o l e f i n s o r f a i l u r e of t h e l i q u i d r e a g e n t s to s w e l l the p o l y m e r s . Similar p r o b l e m s h a v e b e e n r e p o r t e d p r e v i o u s l y (10, 12). O n the o t h e r h a n d , s u c c e s s f u l complete r e a c t i o n s h a v e b e e n r e p o r t e d b e t w e e n g a s e s o r v a p o u r s a n d o x i d a t i o n p r o d u c t s (7, 8, 12, 13, 18). A p p a r e n t l y , s m a l l gas molecules c a n p e n e t r a t e the p o l y ­ mer s t r u c t u r e a n d r e a c h most s i t e s p r e v i o u s l y a c c e s s a b l e to 0 . In t h e f o l l o w i n g s e c t i o n s , some of t h e p r e v i o u s l y p r o p o s e d g a s - p o l y m e r r e a c t i o n s are r e - e x a m i n e d a n d c o m p a r e d with some newly d e v e l o p e d methods. 2

SQ Reactions. E x p o s u r e to S 0 has b e e n p r o p o s e d to lead to a q u a n t i t a t i v e r e a c t i o n with - O O H g r o u p s to g i v e a p r o d u c t with a m a r k e d i n c r e a s e i n IR a b s o r p t i o n o v e r t h a t of the o r i g i n a l - O O H g r o u p s (7, 18). H o w e v e r , we h a v e f o u n d the r e a c t i o n s with o x i d i z e d 9

2

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CARLSSON ET AL.

Products from Polyolefin Oxidation

LLDPE + 2 0 Mrad

WAVENUMBER Figure 1

IR s p e c t r a of p r o d u c t s from gas r e a c t i o n s pre-oxidized LLDPE

with

Film o x i d i z e d i n a i r b y γ - i r r a d i a t i o n (20 M r a d . ) . F T I R s p e c t r a r e s u l t from the s u b t r a c t i o n of t h e s p e c t r u m of n o n - o x i d i z e d L L D P E .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

380

CHEMICAL REACTIONS ON POLYMERS

^ i P P + 10 Mrad

1

t: 4000

,

au 3000

ι

1800

.

ι

1400

.

L _

1000

WAVENUMBER Figure 2

IR s p e c t r a of p r o d u c t s from gas r e a c t i o n s pre-oxidized iPP

with

Film o x i d i z e d i n a i r b y γ - i r r a d i a t i o n (10 M r a d . ) . F T I R s p e c t r a r e s u l t from t h e s u b t r a c t i o n of the s p e c t r u m of n o n - o x i d i z e d i P P .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

27.

C A R L S S O N ET A L .

381

Products from Polyolefin Oxidation

i P P a n d L L D P E to be c o m p l e x , n o n - q u a n t i t a t i v e a n d to g i v e o n l y m a r g i n a l e n h a n c e m e n t i n the IR a b s o r p t i o n o v e r the b a s i c 3400 cm"" absorption. O u r r e s u l t s of s t u d i e s of S 0 r e a c t i o n s on o x i d i z e d p o l y m e r s a n d m o d e l c o m p o u n d s h a v e b e e n r e p o r t e d p r e v i o u s l y (19). The S0 method seems to b e d i s t i n c t l y i n f e r i o r to o t h e r m e t h o d s ( e s p e c i a l l y N O t r e a t m e n t d i s c u s s e d below) a n d w i l l n o t b e c o n s i d e r e d further. 1

2

2

SF Reactions. In c o n t r a s t to S 0 r e a c t i o n s , the SF^ r e a c t i o n as p r o p o s e d o v e r 20 y e a r s ago b y H e a c o c k i s a c l e a n , q u a n t i t a t i v e r e a c ­ t i o n a l t h o u g h with p o t e n t i a l b e y o n d t h a t o r i g i n a l l y p r o p o s e d ( 8 J . From F i g u r e s 1 a n d 2, SF^ e x p o s u r e c a u s e s complete l o s s of a l l - O H a b s o r p t i o n s with the g e n e r a t i o n of - C ( = 0 ) F a b s o r p t i o n s at 1842-1848 cm"" a n d p o s s i b l y weak - C - F a b s o r p t i o n s at ~ 1000 c m " . Oxidized L L D P E a n d i P P give r i s e to d i s t i n c t l y d i f f e r e n t - C ( = 0 ) F a b s o r b a n ces. T h e a b s o r b a n c e i n L L D P E l i e s at 1848 cm" w h e r e a s t h a t from i P P i s at 1842 cm" , with weake s h o u l d e t 1848 c m " Compari s o n s t u d i e s on e x t r e m e l the 1848 cm" a b s o r p t i o b a n d c a n r e a s o n a b l y be a t t r i b u t e d to c h a i n - e n d a c i d f l u o r i d e s ( r e a c ­ t i o n 1). In i P P , c a r b o x y l i c a c i d g r o u p s c a n b e e x p e c t e d from t h e f r e e - r a d i c a l o x i d a t i o n of t h e m e t h y l s i d e g r o u p s , a n d to a l e s s e r k

2

1

1

1

1

1

1

Ο - CH 2 — CH 2 - C

-

CH

CH

0

2

- C

1)

OH e x t e n t from the 3 - s c i s s i o n of a l k o x y l r a d i c a l s ( I ) , r e a c t i o n s e q u e n c e 2. I

/

3

~~ c

CH.

CH CH,

I

• ο

I

p o s s i b l y v i a the

CHo

Q

- CHU

- Ο­ Ι Η

I

-

C~ I Η

Ύ

I I

I R0 2

O

c HD

/

-t \

Η

C RH

/ HDD

I ο-

Ι

Η

CHo

Ο

I

RQ>*

c - c~

ROH

"EH

/ Η

I Η

2)

(R0 take II).

e 2

r e p r e s e n t s a n y p e r o x y l r a d i c a l f o r m e d from i P P , w h i c h will p a r t i n a t e r m i n a t i o n r e a c t i o n with the p r i m a r y p e r o x y l r a d i c a l From a c o m p a r i s o n with a c i d f l u o r i d e s p r e p a r e d from m o d e l

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

382

CHEMICAL REACTIONS ON POLYMERS

acids

(TableII)

V

~CH2

-

the d o m i n a n t 1842 cm"

F

C -

C H

~

2

group

1

a b s o r p t i o n i n P P is from

w h e r e a s t h e 1848 c m

- 1

the

shoulder probably

H comes from the c h a i n - e n d a c i d p r o d u c e d v i a r e a c t i o n 2. In tions,

a d d i t i o n to the c l e a r g e n e r a t i o n of t h e a c i d f l u o r i d e a b s o r p ­

the

SF^ f l u o r i n a t i o n

advantages.

1

which absorb tions), In

or

at ~ 1710 cm"*

as

free,

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complexes

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of

- O H groups

exist

as

very

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non-hydrogen-bonded

carboxylic from

extraneous

acids

take

acids

part

other

dimers,

a c i d IR a b s o r p ­

at 1755

in

has

stable

cm"

1

hydrogen

(20). bonded

1755

through

absorptions

to

~

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cm"

1

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of

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the

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and

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1

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absorption

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which

cause

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This

from

SF

model

that

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polyolefins

complimentary reactions

can

to

at

the

1784

of t h e

b o t h the only

with

ducts).

with

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4

(CH N ) 2

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on

level

of

the

prior

attempted,

are

to

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(
R ! Ο3 f ! Ε j 1 0.G £6 2 Λ 0.113 E-2 Î.00 0.'42 ΤIMEi.;&5 1.1 Ε-4 ..···*'

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F i g u r e 2. Representativ with p e r m i s s i o n from R e f

Figure 4.

, Copyrigh

Pergamo

I n f r a r e d Spectrum of Hydrogenated

Polybutadiene

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

)

400

CHEMICAL REACTIONS ON POLYMERS

3000

2500

2000

1800

cm" F i g u r e 5.

Infrared

1600

1400 1200

1000

800

1

Spectrum of H y d r o f o r m y l a t e d

Polybutadiene

ι oo UJ Ο

z

80


k

^ / V %

ASH

y -

.

(1)

SA OH where ASH -

t - B u ^ t - B U i Q - N H ^ t - B u - r ^ t - B u < (C ^NH-Cf ^NHCOCHgSH CH SH 2

(2)

(3)

However, i t may be more surprising for a s i m i l a r reaction to take place w i t h saturated hydrocarbon polymers such as polypropylene (PP) and polyethylene (PE) since the level of unsaturation i s insufficient. It was shown, however, that in such cases binding takes place in t w o stages (13). Most of the adduct i s formed during the f i r s t minute of processing when the applied shear i s maximum (high polymer viscosity). The f i r s t stage of binding, therefore, involves the formation of macroalkyl radicals by mechanical s c i s s i o n of the polymer chains, (scheme 3). The thiol antioxidant (ASH) i s extremely labile to radical attack; i t attacks the mechanoradical to produce a thiyl radical which then reacts w i t h another mechano chemically-generated radical to form the bound antioxidant.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

418

CHEMICAL REACTIONS ON POLYMERS

The mechanoradical produced w i l l react w i t h the small amount of oxygen to form hydroperoxides; these are subsequently u t i l i s e d as radical generators in the second stage. The resulting hydroxyl radical (from hydroperoxide decomposition) abstracts a hydrogen from the substrate to form macroradical which, in turn, w i l l react w i t h more of the thlyl radical to form more bound antioxidant. The polymer bound antioxidant made in this way is very much more resistant to solvent leaching and v o l a t i l i s a t i o n when compared to commercial additives (13). see Figure 2. R E A C T I V E MODIFIERS FOR POLYMER M O D I F I C A T I O N

Enhancing the properties of the relatively cheap commodity plastics through the use of small amounts of reactive modifiers during melt processing (as in metho A good example of a reactiv enhance properties of polyolefins is maleic anhydride (MA). The formation of maleic adduct in polypropylene (PP), for example, can be used to effect several modifications; e.g. to improving hydrophilicity, adhesion and dyeability. Moreover, the polymer-maleic adduct has an availabla additional functionality to effect other chemical modifications for achieving the desired material design objectives. Reactions of MA w i t h polymers in solution are described in the patent literature (15). We have successfully achieved (Al-Malaika,S., Quinn, N., and Scott, 6., Aston University, Birmingham, unpublished work) i n - s i t u synthesis of maleic-polypropylene adduct during melt processing of the polymer in the presence of MA and free radical initiator. The functionalised polymer adduct was used to introduce further chemical modifications for improving the polymer properties. For example, using the above method, we have achieved improved adhesion to the surface of reinforcing glass and mineral fibres. Chemical attachment of antioxidants was also effected for the purpose of of improving additive performance. Addition reaction of peroxide-generated macroalkyl radicals w i t h the reactive unsaturation in MA is shown in reaction scheme 4. The functionalised maleic-polymer adduct (II, scheme 4) is the product of hydrogen abstraction reaction of the adduct radical (I, scheme 4) w i t h another PP chain. Concomitantly, a new macroalkyl radical i s regenerated which feeds back into the cycle. The frequency of this feedback determines the efficiency of the c y c l i c a l mechanism, hence the degree of binding. Cross-linking reaction of I occurs by route c ( scheme 4). The presence of an active s i t e in the modifier is essential for the formation of polymer-modifier adduct by the i n - s i t u method (method 2 ) above. Figure 3 compares the degree of binding which can be achieved

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

29.

AL-MALAIKA

Reactive Modifiers for Polymers

Α Λ Α

419

A/V:

M

OH + RO-^AS'

SA

ASH =

Control Time of Hot Water Extr., days

Figure 2. Effect of hot ( 1 0 0 * 0 water extraction on impact strength of PP in the absence and presence of a combination of conventional antioxidants (Nickel dibutyl dithiocarbamate and Irganox 1076, NiDBOIrg.1076) and a thiol bound antioxidant (3), Bound AO. (Reproduced w i t h permission from Ref. 13. Copyright 1983 App. Sci. Pub.)

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

420

CHEMICAL REACTIONS ON POLYMERS

scheme A

Figure 3. Effect of reactive s i t e in modifiers (MA is maleic anhydride and SA is succinic anhydride) on binding in unstabilised (U), ICI, HF22, and s t a b i l i s e d (S), ICI HWM25, polypropylene.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

AL-MALAIKA

Reactive Modifiers for Polymers

when using analogous modifiers except f o r the presence (with MA) and absence (with succinic anhydride, SA) of reactive s i t e s (C = C). Up to 55% binding of MA on PP w a s obtained (based on exhaustive Soxhlet extraction w i t h chloroform and acetone) wheras no binding w a s achieved when S A w a s used. The importance of PP-MA adduct formation i s further demonstrated when the above method was used in composites based on glass fibre and PP-MA and P P - S A samples; P P - S A sample exhibited very inferior mechanical properties when compared to the composite system based on PP-MA adduct (see Fig. 4). To achieve optimum conditions f o r the attachment of reactive modifiers to the polymer backbone, oxygen and other radical traps should be avoided since these compete for the same macroalkyl radical s i t e s (scheme l e and I d , see also figure 3, curves MA-U and MA-S). Mechanochemical attachment of MA to both unstabilised (ICI HF22) and stabilised (ICI, HWM25 processing conditions, the degree o binding o the modifie (MA) to PP is t w i c e as much f o r the unstabilised grade. The mechanism of the antioxidant action of thermal s t a b i l i s e r s (11) can account f o r this apparent discrepency. Hindered phenols function by a c y c l i c a l regenerative process involving alternating chain breaking-acceptor (CB-A) and chain breaking-donor (CB-D) antioxidant steps (see reaction scheme 5). Hindered phenols form stable phenoxyl radicals in the presence of alkyl peroxyl radicals. The phenoxyl radicals react w i t h macroalkyl radicals in a C B - A step to reform the hindered phenol which in turn reacts w i t h more alkylperoxyl radicals in a CB-D step to regenerate the phenoxyl radical which then reacts w i t h more alkyl radicals. The central feature of this mechanism is, therefore, that the phenoxyl radical i s reversibly reduced and re-oxidised; this leads to the continuous consumption of macroalkyl radicals. The phenoxyl radical can, therefore, react w i t h polypropylene radicals and compete w i t h PP-MA adduct formation in the stabilised polymer (Figure 3, curve MA-S).

REACTIVE M0P1F1ER5 ANP ADHESION The localised r e a c t i v i t y which has been introduced by tieing the reactive modifier mechanochemically into the otherwise inert PP substrate i s exploited here to promote adhesion to different surfaces, e.g. glass. Homogenisation of glass fibre (in a Buss-Ko kneader at 230* C), which has been treated w i t h an amino-containing silane coupling agent (Union Carbide, A1100), w i t h mechanochemical ly synthesised PP-MA adduct (using PP grade HF22) results in considerable improvement in mechanical properties. Figure 4 shows that the

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

421

422

CHEMICAL REACTIONS ON POLYMERS

modified unstabilised PP composite does not only offer much improved mechanical performance over the hindered phenol stabilised and modified PP composite analogue but is also considerably better than a commercial control of 3 0 » glass reinforced PP (ICI, HW60/6R30). The amide linkage resulting from the condensation reaction between the functionalities on the modifier adduct and the silane coupling agent (reaction scheme 6), which takes place during the homogenisation process, was confirmed by IR spectroscopy. The improved mechanical properties (see Figure 4) are attributed to amide linkages which promote better glass-polymer adhesion. Examination of scanning electron micrographs of tensile fractured surfaces of the modified reinforced unstabilised PP and the hindered phenol stabilised analogue ( F i g u r e s 5 and β ) shows clearly that fractured surfaces of the former exhibit short fibre pull-out (plate 1) compared to the much The short fibre pull-ou higher mechanical p e r f o r m a n c e , see Figure 4) as a result of increased adhesion between the fibre and the modified polymer interfaces. The extent of this adhesion must be a function of the level of maleic adduct present in the reactively-modified PP surface which consequently provides the neccessary functionality at the interface to enable condensation reactions to take place w i t h the amino groups (giving r i s e to the amide linkages observed) of the coupling agent on the glass surface (compare curves MA-S and MA-U, Figure 3).

Figure 4. Comparison of mechanical properties of, ^%%3 30% glass reinforced MA-modifiedPP (unstabilised, ICI-HF22), Y///X commercial control of 30% glass reinforced PP (ICI-HW60/GR30), t ^ % j 30% glass reinforced MA-modified PP (stabilised, ICI-HWM25), [•v»y^ 30% glass reinforced SA-modified PP (unstabilised, ICI-HF22).

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

29. A L - M A L A I K A

Reactive Modifiers for Polymers

423

ί ί- 0-Si-(CH L-NH + 2

2

I

Polymer

Citas s

Ο

S u r f ace

C/)

S u r f ace

LU

°

H

0-Si-(CH )-NH-C-CHO-C-C - I 0 * ' 2

Ρ D Cy m er

Ci t a s s

Surface

Surface scheme

6

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

424

CHEMICAL REACTIONS ON POLYMERS

F i g u r e 5. Scanning e l e c t r o n m i c r o g r a p h o f t e n s i l e f r a c t u r e d s u r f a c e o f 30% g l a s s r e i n f o r c e d MA-modified PP ( u n s t a b i l i s e d , 1C1-HF22).

Figure 6. Scanning e l e c t r o n m i c r o g r a p h o f t e n s i l e f r a c t u r e d s u r f a c e o f 30% g l a s s r e i n f o r c e d MA-modified PP ( s t a b i l i s e d w i t h h i n d e r e d p h e n o l , 1C1-HWM25).

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

29.

AL-MALAIKA

Reactive Modifiers for Polymers

ACKNOWLEDGMENT? The author i s grateful to Professor G. Scott and Dr Ν. Quinn f o r preliminary publication of results which w i l l be published in full elsewhere.

LITERATURE CITED 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

Kauzman, W.; Eyring,H.,J. Am. Chem. Soc. 1940, 62, 3113. Ayrey, G.; Moore, C.G.; Watson, W.F., J. App. Polym. Sci. 1956, 19, 1. Ceresa, R.J.; Watson, W.F., J. App. Polym. Sci. 1959, 1, 101. Thomas, D.K., in Developments in Polymer Stabilisation-1 Scott G., Ed.; App. Sci. : London Scott, G., in Development Polyme , , Ed.; App. Sci. : London, 1981;ch.6. Gupta, Fu.s.; Albertson, A.C.; Vogl, O., in New Trends in the Photochemistry of Polymers , Allen, N.S., and Rabek, J.F., Ed. ; Elsevier App. Sci. : London, 1985; Ch. 15. Scott, G., Pure and App. Chem., 1983,55,128 and 1615. Scott, G., Polym. Eng.Sci.,1984, 24, 1007. Meyer, G.E.; Kavchok, R.W.; Naples. T.F., Rubb. Chem. Tech., 1973. 46, 106. Al-Malaika,S.; Honggokosomo, S.; Scott, G., Polym. Deg. Stab., 1986, 16, 25. Al-Malaika, S.; Scott, G., in Degradation and Stabilisation of Polyolefins, Allen, N.S., Ed. ; App. Sci. : London, 1983, Ch.6. Ghaemy, M.; Scott,G.,Polym. Deg. Stab., 1980-81, 3, 405. Scott, G.; Setoudeh.E., Polym. Deg. Stab., 1983, 5, 1. Culbertson, B.M.; Trivede, B.C., in Maleic Anhydride: Plenum: NY, 1982, Ch.11. Hercules Inc., US Pat., 3,437,556; 1969.

RECEIVED October 30, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

425

Chapter 30

Phase-Transfer-Catalyzed Modification of Dextran Employing Dibutyltin Dichloride and Bis(cyclopentadienyl)titanium Dichloride 1

Yoshinobu Naoshima and Charles E. Carraher, Jr.

2

1

Department of Chemistry, Okayama University of Science, Ridai-cho, Okayama 700, Japan Department of Chemistry, Florida Atlantic University, Boca Raton, FL 33431 2

The modification of dextran was achieved employing dibutyltin dichloride and bis(cyclopentadienyl)titanium dichloride using the aqueous interfacial condensation system. The condensatio phase transfer agen molar ratio. The parameters of percentage product yield and location of the maximum as the molar ratio of reactants is varied were employed to discern if the added phase transfer agents were functioning as a phase transfer agent. For condensations involving the titanocene dichloride, all of the employed phase transfer agents are believed to act as phase transfer agents when employing either sodium hydroxide or triethylamine as the added base. Further, triethylamine itself appears to act as a phase transfer agent. When the organostannane is employed similar results are obtained with the exception that the product percentage yields are generally less for systems employing triethylamine compared with systems employing sodium hydroxide. The roles of triethylamine for such systems is presently unknown. Carbohydrates are the most abundant, weight-wise, organic mater i a l available. Photosynthesis produces about 400 b i l l i o n tons annua l l y . The polysaccharides are generally composed of mono- and d i saccharide units. Dextran was chosen t o study f o r the following reasons. F i r s t , i t i s water soluble allowing three dimensional modification employing aqueous solution and c l a s s i c a l i n t e r f a c i a l condensation routes. Second, i t i s r e a d i l y available i n i n d u s t r i a l quantities. Third, i t i s available i n a range of molecular weight allowing product modif i c a t i o n t o be studied as a function of dextran chain s i z e . Fourth, i t i s generally considered t o be an under-utilized natural feedstock. Dextran i s the c o l l e c t i v e name of e x t r a c e l l u l a r b a c t e r i a l polyalpha-D-glucopyranoses linked largely by 1,6 bonds, with branching occurring a t the 1,2, 1,3 or 1,4 bonds. Physical properties vary 0097-6156/88/0364-0426$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

30. N A O S H I M A A N D C A R R A H E R

Modification

of Dextran

427

according t o the amount and manner of branching, nature of endgroup, molecular weight and molecular weight d i s t r i b u t i o n , processing, etc. Dextran i s produced from sucrose by a number of bacteria the major ones being the nonpathogenic bacteria Leuconostoc mesenterodes and Leuconostoc dextranicum. As expected, the structure (and conse­ quently the properties) of the dextran i s determined by the p a r t i c u ­ l a r s t r a i n that produces i t . Dextran i s the f i r s t microbial polysaccharide produced and u t i ­ l i z e d on an i n d u s t r i a l scale. The potential importance of dextran as a s t r u c t u a l l y (and property) controlled feedstock i s c l e a r l y seen i n l i g h t of the recent emphasis of molecular b i o l o g i s t s and molecular engineers i n the generation of microbes f o r feedstock production. Dextran i s employed as pharmaceuticals (additives and coatings of medications), within cosmetics, as food extenders, as water-loss i n ­ h i b i t o r s i n o i l w e l l d r i l l i n g muds and as the basis f o r a number of synthetic resins. Svenska Sockerfabrik Aktiebolaget f o Aktiebolaget Pharmaci i n Sweden began large scal By 1947, Dextran Ltd. (Eas duction of dextran and i n 1949 Commercial Solvents Corp. (USA) began production (2,3). In 1952, the R. K. Laros Co. (3) began the enzymic production of dextran i n the presence of l i v i n g c e l l s . In an e f f o r t to standardize the dextran produced, by 1952, the majority of compa­ nies employed the L. mesenteroides NKRL B-512-(f) i n the production of dextran. The production of dextran involves mixing the appropri­ ate quantities of sucrose and enzyme under prescribed conditions. S o l u b i l i t y generally decreases with increase i n chain s i z e and extent of branching. The s o l u b i l i t y of dextran can be divided into four groups — those that are r e a d i l y soluble at room temperature i n water, DMF, DMSO and d i l u t e base; those that have d i f f i c u l t y d i s s o l v ­ ing i n water; those that are soluble i n aqueous solution only i n the presence of base; and, those that are soluble only under pressure, a t high temperatures (> 100°C) and i n the presence of base. Dextran B-512 readily dissolves i n water and 6M, 2M glycine and 50% glucose aqueous solutions. Dextran B-512, dissolved i n water, approaches a form of compact s p h e r i c a l - l i k e h e l i c a l c o i l s (4-6). Streaming, birefringence meas­ urements indicate that the dextran has some f l e x i b i l i t y . The B-512 dextran shows a r e f r a c t i v e index increment, dn/dc, of 0.154 ml/g a t 436 mu i n water and an apparent radius of gyration i n water on the order of 2 χ 10 A. Branching occurs through about 5% of the units through the 1,3 linkage with about 80% of these branches being only one unit i n length. There e x i s t s a few, less than 1%, long branches i n B-512 dextran (6). Chemically dextrans are similar to one another. The a c t i v a t i o n energy f o r a c i d hydrolysis i s about 30-35 Kcal/mol (_5 ). The C-2 hydroxyls appear to be the most reactive i n most Lewis base and a c i d type reactions. A wide v a r i e t y of esters and ethers have been de­ scribed as well as carbonates and xanthates (2/8.)· a l k a l i n e solu­ t i o n , dextran forms a varying complex with a number of metal ions I

n

(£). The b i o l o g i c a l properties of dextran again vary with s t r a i n . The B-512 i s d i g e s t i b l e i n mammalian tissues as the l i v e r , spleen, and kidneys, but not i n the blood ( 1_0 ). I t appears not t o stimulate

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

428

formation of antibodies i n man upon intravenous infusion ( 1_). On the other hand, subcutaneous i n j e c t i o n i n humans led to skin s e n s i t i v i t y and to the formation of p r e c i p i t a t i n g antibodies (1J_). Antibody f o r ­ mation and p r e c i p i t a t i o n with antiserums decreases as chain length increases (Y\_,V2). Linear, water-soluble dextrans have many uses. One dextran i s employed i n viscous water-flooding f o r secondary recovery of petro­ leum with a potential market of about 2 x 1 0 tons per year. This dextran i s superior to carboxymethyl c e l l u l o s e when employed i n high calcium d r i l l i n g muds ( V3,J_4). These dextran-muds show superior s t a ­ b i l i t y and performance at high pH and i n saturated brines (15-17). Other dextrans show good resistance to deterioration i n s o i l and the a b i l i t y to s t a b i l i z e aggregates (1_8) i n s o i l s . They can also be used i n binding collagen f i b e r s i n t o s u r g i c a l sutures (19). An underlying assumption i s that dextran i s a representative polysaccharide and that r e s u l t s derived from i t s study can be applied to other polysaccharides Effected modifications are intended to occur throughout the dextra face. This i s achieved dextran. Recently Carraher, Naoshima and coworkers effected the modifica­ t i o n of polysaccharides employing organostannanes and bis(cyclopentadienyl)titanium d i c h l o r i d e , BCTD (20-25). Here we report the modifi­ cation of dextran employing the i n t e r f a c i a l condensation technique using various phase transfer agents u t i l i z i n g BCTD and d i b u t y l t i n d i ­ chloride, DBTD. Experimental Reactions were c a r r i e d out employing a one quart Kimex emulsify­ ing j a r placed on a Waring Blendor (Model 7011G) with a no load s t i r ­ r i n g rate of about 20,000 rpm. The following organic chemicals were used as received (from A l d r i c h unless otherwise noted): b i s ( c y c l o pentadienyl)titanium d i c h l o r i d e , d i b u t y l t i n d i c h l o r i d e , 18-crown-6, dibenzo-18-crown-6, tetra-n-butylammonium hydrogensulfate (Tokyo Kasei Kogyo Co., Ltd., Japan), triethylamine (Wako Pure Chemical In­ dustries, Japan), and dextran (Wako Pure Chemical Industries; molecu­ l a r weight = 2 to 3 χ 10 ). In a t y p i c a l procedure, an aqueous solu­ t i o n of dextran containing a base and a phase transfer catalyst (PTC) was added rapidly s t i r r e d solutions of the organometallic d i c h l o r i d e i n chloroform. Repeated washings with organic solvent and water as­ s i s t e d i n the product p u r i f i c a t i o n . Elemental analyses f o r titanium and t i n were conducted employing the usual wet analysis procedure with HC10 . Infrared spectra were obtained using Hitachi 260-10 and 270-30 spectrometers and a D i g i l a b FTS-IMX FT-IR. EI mass spectral analysis was c a r r i e d out employing a JEOL JMS-D300 GC mass spectro­ meter connected with a JAI JHP-2 Curie Point Pyrolyzer. DT and TG analyses were performed employing a SINKU-RIKO ULVAC TGD-500M or a DuPont 990 TGA and 900 DSC. 4

Results and Discussion Structural characterization was based on s o l u b i l i t y , thermal and elemental analyses, and infrared and mass spectroscopies. Charac-

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

30.

NAOSHIMA AND CARRAHER

Modification

of Dextran

429

t e r i z a t i o n r e s u l t s were i n agreement with the product being composed of units, including unreacted u n i t s , as depicted i n Figures 1 and 2 and reported i n references 21_, _24 and 25. The investigation of the chemical modification of dextran t o determine the importance of various reaction parameters that may eventually allow the controlled synthesis of dextran-modified mater i a l s has began. The i n i t i a l parameter chosen was reactant molar r a t i o , since t h i s reaction v a r i a b l e has previously been found t o greatly influence other i n t e r f a c i a l condensations. Phase transfer c a t a l y s t s , PTC's, have been successfully employed i n the synthesis of various metal-containing polyethers and polyamines (for instance 26). Thus, the e f f e c t of various PTC's was also studied as a funct i o n of reactant molar r a t i o . Two parameters were employed i n evaluating i f an added PTC i s functioning as a PTC. These parameters were percentage y i e l d and p o s i t i o n of the maximum as the molar r a t i o of reactant i s varied. If PTC a c t i v i t y i s occurring thes parameter might follow : a. d i f f e r i n g , normall added PTC compared with b. change i n the p o s i t i o n of the maximum i n percentage y i e l d . The maximizing of y i e l d as the molar r a t i o i s varied i s common f o r i e t e r f a c i a l systems (for instance 27-29). The molar r a t i o corresponding to the maximum y i e l d corresponds t o a favorable balancing of the ent r y of the reactants into the reaction zone. For a given set of r e actants t h i s maximin w i l l vary dependent on the s p e c i f i c reaction parameters. Thus factors that a f f e c t the r e l a t i v e transport factors w i l l a f f e c t the p o s i t i o n of the maximum whereas factors that do not a f f e c t these transport factors w i l l r e s u l t i n maximums occurring i n the same general area as the molar r a t i o i s varied. Increased y i e l d i s a l s o consistent with an increase i n the reactants reaching the r e action zone during the reaction. For the present study, y i e l d d i f ferences can be considered as r e l a t i v e measures o f transport f a c t o r s . A t h i r d , less dependable parameter that may be a measure of PTC a c t i v i t y i s percentage organometallin incorporation. Percentage i n corporation i s believed t o be less dependable f o r the following reasons. F i r s t , s t e r i c factors appear t o be c r i t i c a l f o r many analogous polymer modification of p o l y ( v i n y l alcohol) and polyethyleneimine (for instance 30-33). Second, f o r the current systems, only moderate differences i n percentage incorporation are found and these d i f f e r ences are believed t o be mainly due d i r e c t l y t o the difference i n molar r a t i o of reactant. As with most analogous cases involving polymer modification, generally high proportions of incorporation are found regardless of percentage y i e l d (for instance 30-33). Tables I-IV contain r e s u l t s as a function of i n i t i a l base, presence or absence of an added PTC, organometallin reactant and molar r a t i o of reactants. On a s t r i c t l y molar r a t i o of reactant s i t e s bas i s , the balancing of net quantity of reactants should occur a t an organometallic/dextran molar r a t i o of 3:2. The present studies are consistent with e a r l i e r studies that showed the maximums occurring away from t h i s 3:2 r a t i o . The values c i t e d i n Table V f o r reactant muximums should be considered only as general. Results contained i n Table I w i l l be u t i l i z e d t o i l l u s t r a t e how the parameters of percentage y i e l d and p o s i t i o n of the maximum of precentage y i e l d as reactant molar r a t i o i s varied might be employed t o indicate i f the added PTC

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

430

CHEMICAL REACTIONS ON POLYMERS

_3_

Bu

Bu

S n = 37°/o

Sn=41%

Figure 1. Possible structures of the tin-containing units.

Ti =17 %

Ti = 2 3 %

-Cp Ti-0-

-Cp Ti-0-

2

2

-Cp Ti-02

Λ 1

Cp

Ti = 23 %

° \ TiCpfX 1

Cp

Ti = 27°/·

Figure 2. Possible structures of the titanium-containing units.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

30.

NAOSHIMA AND CARRAHER Table

I

.

Results for

as

funet ion

of

base

c o n t a i n i n g TBAHS

systems

catalyst, A.

a

Modification

of Dextran

and amount

or

no

431

of

DBTD

trans fer

phase

PTC

T r i e t h y l amine Bu SnCl2

Yield

(mmo1)

(%)

2

a

PTC

PTC

0.008

29

29

0.05

29

29

0.14

0.11

28

37

38

0.14

0.28

41

37

4

0.07

1 .00

29

19

0.07

2 .00

28

22

3.00

19 7

water;Bu SnCl 2

B.

None

0.015

7

( 3 . OOmmol), in

2

TEA

(9.00mmol)

CHC1 ;30ι

50ml

None

PTC

None

12

4.00

(%)

(g)

0.50

(Dextran

Sn

Yield

3

37

28

0.035

a n d TBAHS

( 0 . 90mmol)

s e c . s t i r r i n g

in

50ml

time.)

NaOH 0.50

57

21

0.14

0.05

27

28

2 .00

83

90

0.41

0.44

23

37

3 .00

4

94

0.025

0.70

39

25

4.00

0

0

(Ibid, and a.

37

1 .00

above

90 s e c .

Yields

Π .

unit

for as

s y s terns

catalyst,

(9.OOmmol)

in

-

place

of TEA

presence

of

Tables

, Π

I

function

a

containing

three

of

Bu Sn

units

2

per

a n d VI . base

a n d amount

18- c r o w n - 6

or

no

of

DBTD

phase

transfer

PTC

Triethylamine Bu SnCl 2

Sn

Yield

Yield

2

(mmo1)

(%)

(%)

(g)

None

None

PTC

0.50

16

7

0.02

0. 008

37

29

1 .00

37

19

0.09

0.05

29

29

2 .00

61

22

0.30

0.11

28

37

3.00

24

38

0.17

0.28

29

37

4

0.15

0. 035

28

37

None

PTC

15

4.00

( 3 . OOmmol),

(Dextran 50ml B.

NaOH

0

t ime.)

on t h e

Results for

A.

employing

s t i r r i n g

based

saccharide Table

except

0

water

TEA in

;Bu SnCl2 2

PTC

a n d 1 8 -• c r o w n - - 6

(9.OOmmol) 50ml

C H C 1 ! ; 30 s e c . 3

(0.90mmo1)

s t i r r i n g

time.)

in

NaOH 0.50

25

8

0 . 03

0.01

23

30

1 .00

82

21

0.20

0 . 05

29

28

2 .00

97

90

0 . 48

0.44

29

37

3 .00

98

94

0.73

0.70

27

25

0

0

4.00 (Ibid, and

above

90 s e c .

excep t

employing

s t i r r i ng

Source: Reproduced Longman.

0 NaOH

0

(6.OOmmol)

-

in

place

of TEA

t i me.)

w i t h p e r m i s s i o n from Ref . 34.

C o p y r i g h t 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

CHEMICAL REACTIONS ON POLYMERS

432

Table

ΠΙ .

Results for

as

catalyst, A.

of

base

TBAHS

and

or

amount

no

phase

of

BCTD

transfer

PT

2

T i C l

2

Y i e l d

Yield

(%)

(g)

(mmol)

Ti (%)

PTC

None

PTC

None

PTC

0.50

ï~5

24

0.02

0.03

12

7~

1.00

78

56

0.19

0.14

12

9

None

2.00

77

67

0.38

0.33

18

12

3.00

69

46

0.51

0.34

17

21

1

0.28

0.01

21

4.00 (Dextran

28 (3.00mmol),

w a t e r ; C p

2

T i C l

2

in

TEA

50ml

(9.00mmol) CHC1 ;30 3

and

sec.

TBAHS

18

(0.90mmol)

s t i r r i n g

in

50ml

time.)

NaOH 0 .. 5 0

0

0

0

0

1. . 0 0

0

0

0

0

-

2.. 0 0

79

0

0.39

0

13

3,. 0 0

69

58

0.52

0 . 43

15

14

4,. 0 0

77

60

0.77

0.60

14

13

(Ibid, and b.

function

containing

Triethylamine C p

B.

a

systems

90

above sec.

Yields

except

based

saccharide

employing

s t i r r i n g

NaOH

(9.00mmol)

in

place

-

of

TEA

time.)

on

the

presence

unit

for

Tables

ΙΠ

of

three

and

Cp Ti 2

units

per

IV .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

30.

NAOSHIMA AND CARRAHER

Table

IV .

Results for

as

catalyst, A.

a

systems

function

containing

base

and amount

18-crown-6

or

no

433

of

BCTD

phase

transfer

PTC

2

T i C l

Yield

2

(mmol)

Yield

(%)

Ti

(g)

PTC

(%)

Non

0.50

5

24

1.00

4

56

0.01

0.14

12

9

2.00

16

67

0.08

0.33

15

12

3.00

25

46

0.18

0.34

17

21

4.00

39

1

0.38

0.01

21

18

(Dextran 50ml

O.OOmmol),

w a t e r ; C p

2

T i C l

TEA in

2

(9.00mmol) 50ml

and

CHC1 ;30 3

18-crown-6

sec.

s t i r r i n g

(0.90mmol)

in

time.)

NaOH 0.50

0

0

0

0

-

1 .00

0

0

0

0

-

-

2.00

0

0

0

0

-

-

3.00

80

58

9

14

4.00 (Ibid, and C.

of

of Dextran

Triethylamine C p

B.

Modification

above

90 s e c .

59 except

60 emp1oyi ng

s t i r r i ng

NaOH

0.59

0 . 43

0.59

0.60

( 6 . OOmmol)

in

-

13

15 pi ace

of

TEA

t i me.)

NaOH 0.50

0

0

0

0

-

1 .00

0

0

0

0

-

2 . 00

21

0

0.11

0

-

17

-

3.00

86

48

0.64

0 . 36

17

17

4.00

86

53

0.86

0.53

21

21

(Ibid, and

-

90

above s e c .

excep t

e m p 1 o y i n g NaOH

s t i r r i n g

( 9 . OOmmo1)

in

pi ace

of

TEA

time.)

Source: Reproduced w i t h p e r m i s s i o n from Ref. 34. C o p y r i g h t 1987 Longman.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

434

CHEMICAL REACTIONS ON POLYMERS

Table OM

I n i t i a l

V

2

SnCl

2

T i C l

"+"

not OM

results Maximum

Variation

Variation

NaOH

TBAHS

+

TEA

18-C-6**

Maximum OM/Dextran*

2

a

+

2/1

+

2/1

+

0

3/1

TEA

DB-18-C-6***

+

+

2/1

NaOH

DB-18-C-6

+

0

3/1

TEA

TBAHS

+

+

>4/l

+

3/1

18-C-6

NaOH

TBAHS

TEA

18-C-6

+

1/3

NaOH

18-C-6

+

2/3

indicates

0

PTC

TEA

2

employing

of

PTC

NaOH

C p

Summary

Yield

Base

Bu

.

Added

that

PTC

a

with

v a r i a t i o n results

indicates

that

the

indicates

that

there

exists

obtained

trends

are

appears

between not

results

employing

a

obtained PTC.

similar. to

be

a

v a r i a t i o n ,

but

it

is

pronounced. is

•for

organometal1ic PTC

containing

**18-crown-6.

reactant. systems.

***dibenzo-18-crown-6.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

30.

NAOSHIMA AND CARRAHER

Modification

of Dextran

435

i s functioning as a PTC. F i r s t , percentage y i e l d s vary between systems employing an added PTC and those not containing an added PTC consistent with the addition of the PTC acting t o influence the transport of the reactants. Second, the maximums vary with respect to the presence or absence of the added PTC. For triethylamine (TEA) systems with tetra-n^-butylammonium hydrogensulfate (TBAHS), the percentage y i e l d maximum occurs near a DBTD/dextran r a t i o of 1/3; f o r the analogous systems except omitting the PTC, the maximum occurs around 3/3. For systems employing sodium hydroxide as the added base, the maximum occurs around 2/1 when the TBAHS i s present and around 3/1 when no PTC i s present. The r e s u l t s are consistent with TBAHS acting t o influence the transport of reactants. Results f o r other PTC's appear i n Table V and are consistent with PTC's functioning t o influence the transport of one or both of the reactants f o r the vast majority of the cases. Triethylamine i s believed t o act as a phase transfer agents (PTA) some i n t e r f a c i a l systems (for instance 26). The maximum percentag y i e l d f o th modificatio effected employing d i b u t y l t i n d i c h l o r i d dextran; Table I) but wit ing 2 mmols of organostannane and greater. The approximate maximums (Table V) and y i e l d f o r PTC-containing systems vary with respect t o the nature of i n i t i a l l y added base (sodium hydroxide or TEA). With the exception of coincidence of the maximums f o r non PTC-containing systems, the evidence i s consistent with the presence of the TEA a f f e c t i n g the general outcome of the reaction. With most of the systems (Tables I, II) the percentage y i e l d s are lower when TEA i s employed. For these systems, i t i s not presently known i f TEA acts as a PTA or i n some other manner. The product of d i b u t y l t i n d i c h l o r i d e and TEA i s brown colored and not water soluble. The modified product i s white, eliminating the p o s s i b i l i t y that the product contains s i g n i f i c a n t portions of the simple organostannane-TEA product. For systems employing BCTD the s i t u a t i o n i s d i f f e r e n t . The maximums occur a t about 2/3 when employing TEA but no PTC and 4/3 when employing sodium hydroxide but no PTC. Again the maximums are dependent on the nature of the added base and added PTC. Yields vary but are not consistently lower when employing TEA compared with sodium hydroxide. I t i s possible that TEA may act t o influence the transport of one or both of the reactants f o r systems employing the organotitanium reactant. Addition of base i s intended t o serve two primary functions. F i r s t , t o act as a scavenger, n e u t r a l i z i n g hydrogen chloride e l i m i nated through condensation between the organometallic d i c h l o r i d e and dextran. Second, t o further activate, polarize the Lewis base f o r more ready attack a t e l e c t r o p h i l i c s i t e s . . Sodium hydroxide, a strong base, i s believed t o further polarize Lewis bases such as amines and hydroxyls whereas TEA does not provide t h i s added assistance t o as great of an extent (see £)· I t i s possible that t h i s further p o l a r i zation of the dextran-hydroxyl groups by the sodium hydroxide i s r e sponsible f o r the r e l a t i v e l y larger y i e l d s found compared t o systems employing TEA as the added base when DBTD i s used. I t i s possible that BCTD i s s u f f i c i e n t l y more reactive than DBTD such that additiona l p o l a r i z a t i o n of the hydroxyls by the hydroxide ion i s not s i g n i f i cant t o outcome of the reaction. While the terms phase transfer c a t a l y s t and phase transfer agent

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

436

CHEMICAL REACTIONS ON POLYMERS

are often employed interchangeably, the term PTA i s broader and i n ­ cludes additives that become part of the o v e r a l l reaction product. In the present study, the TEA i s a PTA but not a PTC since i t has been found t o react with both of the metal-containing reactants. For the present products, TEA-containing moieties have been indicated em­ ploying both infrared and mass spectroscopies (24). An additional question concerns whether the location of the PTC has an e f f e c t on the reaction. Table VI contains r e s u l t s where 18crown-6 was added t o the either phase. I t appears that the i n i t i a l location of the 18-crown-6 has l i t t l e or no e f f e c t on the reaction.

Table

VI .

Results for

Bu

2

SnCl

the

as PTC

a

function

of

DBTD

(mmo1)

origi nal

1 ocat ion

Sn

Yield

Yield

2

and

1 8 - c r o w n -•6

(%) None

OR*

Wate

8

20

25

0.01

0.025

0.03

30

37

23

1.00

21

75

82

0.05

0.19

0.20

28

29

29

0. 50

2.00

90

91

97

0.44

0 . 45

0. 48

37

37

29

3.00

94

97

98

0.70

0.72

0.73

25

28

27

4.00

0

0

0

0

0

0

-

-

-

Dextran added

(3.OOmmol)

to

s t i r r i n g

s t i r r e d

and

s o d i u m h y d r o x i de

solutions

of

Bu SnCl 2

2

( 6 . OOmmol) in

50ml

iη

CHClg

50ml wi t h

water 90

:s e c .

time.

•Organ i c.

Literature Cited 1. Gronwall, A. Dextran and Its Use in Colloidal Solutions; Academic Press, New York, 1957. 2. Mfg. Chemist 1952, 23(2), 49. 3. Chem. Eng. 1952, 59, 215(Sept.) and 240(Dec.). 4. Oene, Η. V.; Cragg, L. H. J. Polymer Sci. 1962, 57, 175. 5. Antonini, E.; Bellelli, L.; Bruzzeni, A.; Caputo, A.; Chiancone, E.; Rossi-Fanelli, A. Biopolymers 1964, 2, 35. 6. Bovey, F. J. Polymer Sci. 1959, 35, 167 and 183. 7. Baker, P. J. Dextrans; Academic Press, New York, 1959.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

30.

NAOSHIMA AND CARRAHER

Modification

of Dextran

437

8. Flodin, P. Dextran Gels and Their Applications in Gel Filtration; Halmatd, Uppsala, 1962. 9. Rowe, C. E. Ph. D. Thesis, Univ. Birmingham, 1956. 10. Fischer, E.; Stein, E. Dextranases; Academic Press, New York, 1960. 11. Kabat, E. Bull. Soc. Chim. Biol. 1960, 42, 1549. 12. Hehre, E.; Sugg, J.; Neill, J. Ann. Ν. Y. Acad. Sci. 1952, 55, 467. 13. Monaghan, P; Gidley, J. Oil Gas J. 1959, 57, 100. 14. Dumbauld, G.; Monaghan, P. U. S. Patent 3,065,170, 1962. 15. Mueller, Ε. Z. Angew. Geol. 1963, 9, 213. 16. Owen, W. Sugar 1952, 47(7), 50. 17. Owen, W. U. S. Patent 2,602,082, 1952. 18. Novak, L.; Witt, E.; Hiler, M. Agr. Food Chem. 1955, 3, 1028. 19. Novak, L. U. S. Patent 2,748,774, 1956. 20. Carraher, C. E.; Giron, D. J.; Schroeder, J. Α.; Mcneely, C. U. S. Patent 4,312,981 1982 21. Naoshima, Y.; Hirono 1985, 2, 43. 22. Carraher, C. E.; Gehrke, T. G.; Giron, D. J.; Cerutis, D.; Molloy, Η. M. J. Macromol. Sci.-Chem. 1983, A19, 1121. 23. Carraher, C. E.; Burt, W. R.; Giron, D. J.; Schroeder, J. Α.; Taylor, M. L.; Molloy, H. M.; Tiernan, T. O. J. Appl. Polym. Sci. 1983, 28, 1919. 24. Naoshima, Y.; Carraher, C. E.; Hess, G. G. Polym. Mat. Sci. Eng. 1983, 49, 215. 25. Naoshima, Y.; Hirono, S.; Carraher, C. E. Polym. Mat. Sci. Eng. 1985, 52, 29. 26. Mathias, L. J.; Carraher, C. Ε., Eds. Crown Ethers and Phase Transfer Catalysis in Polymer Science; Plenum Press, New York, 1984. 27. Morgan, P. W. Condensation Polymers:By Interfacial and Solution Methods; Wiley, New York, 1965. 28. Millich, F.; Carraher, C. Ε., Eds. Interfacial Synthesis, Vols. I and II; Dekker, New York, 1977. 29. Carraher, C. E.; Preston, J., Eds. Interfacial Synthesis, Vol. III; Dekker, New York, 1982. 30. Carraher, C. E.; Tsuda, Μ., Eds. Modification of Polymers; American Chemical Society, Washington, D. C., 1980. 31. Carraher, C. E.; Moore, J. Α., Eds. Modification of Polymers; Plenum Press, New York, 1983. 32. Carraher, C. E.; Feddersen, M. F. Angew. Makromolekulare Chemie 1976, 54, 119. 33. Carraher, C. E.; Ademu-John, C.; Fortman, J. J.; Giron, D. J.; Turner, C. J. Polymer materials 1984, 1, 116. 34. Naoshima, Y., Applied Organometallic Chemistry 1987, 1, 245-249. RECEIVED October

30, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 31

Cross-Linking of Ethylene-Propylene Copolymer Rubber with Dicumyl Peroxide-Maleic Anhydride Norman G. Gaylord, Mahendra Mehta, and Rajendra Mehta Gaylord Research Institute, Inc., New Providence, ΝJ 07974 The reaction of EP yielded a fractio presence of maleic anhydride (ΜΑΗ) in the EPR-DCP reac­ tion mixture increased the amount of cyclohexane-insol­ uble gel. However, the gel concentration decreased as the DCP concentration increased. The ΜΑΗ content of the soluble polymer increased when either the ΜΑΗ or the DCP concentration increased. The molecular weight of the soluble polymer increased with increasing ΜΑΗ concentra­ tion and decreased with increasing DCP concentration in the reaction mixture. The products from the EPR-DCP and EPR-MAH-DCP reactions were soluble in refluxing xylene and were fractionated by precipitation with acetone. The presence of stearamide in the EPR-MAH-DCP reaction in­ creased the amount and the molecular weight of the cyclo­ -hexane-soluble polymer. The c r o s s l i n k i n g o f e t h y l e n e - p r o p y l e n e c o p o l y m e r r u b b e r (EPR) i n t h e p r e s e n c e o f o r g a n i c p e r o x i d e s has been i n v e s t i g a t e d by N a t t a and/or h i s coworkers (1-3) and o t h e r s ( 4 , 5 ) . C o - a g e n t s s u c h a s s u l f u r (3,4) and u n s a t u r a t e d monomers ( 6 j , i n c l u d i n g m a l e i c a n h y d r i d e (ΜΑΗ)(3,7) have been u t i l i z e d i n an e f f o r t t o i n c r e a s e t h e c r o s s l i n k i n g e f f i ­ c i e n c y i n t h e E P R - p e r o x i d e system. As p a r t o f o u r c o n t i n u i n g s t u d y o f t h e p e r o x i d e - c a t a l y z e d r e a c ­ t i o n s o f ΜΑΗ w i t h s a t u r a t e d p o l y o l e f i n s , t h e p r e s e n t i n v e s t i g a t i o n was u n d e r t a k e n t o d e t e r m i n e t h e e x t e n t o f c r o s s l i n k i n g and/or d e g r a d ­ a t i o n which accompanies t h e EPR-MAH r e a c t i o n . The g e l c o n t e n t , p r e ­ sumably i n d i c a t i v e o f c r o s s l i n k i n g , was d e t e r m i n e d by e x t r a c t i o n w i t h c y c l o h e x a n e a t room temperature (22°C) f o r 60 h r . EXPERIMENTAL EPR REACTIONS. V i s t a l o n 404 EPR (Exxon C h e m i c a l Co.)(40/60 wt r a t i o E/P, / M 37) was f l u x e d f o r 2 min i n t h e m i x i n g chamber o f a B r a bender P l a s t i c o r d e r a t 60 rpm and 180°C. A m i x t u r e o f DCP, ΜΑΗ and s t e a r a m i d e ( S A ) , when p r e s e n t , was added i n f o u r p o r t i o n s a t 2 min i n t e r v a l s t o t h e 40g f l u x i n g EPR. A f t e r t h e l a s t a d d i t i o n , m i x i n g M

w

n

0097-6156/88/0364-0438$06.00/0 © 1988 American Chemical Society

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31.

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was c o n t i n u e d f o r 2 min ( t o t a l 10 min) and then t h e r e a c t i o n m i x t u r e was q u i c k l y removed from the chamber. CYCLOHEXANE EXTRACTION. A 5-6g p o r t i o n o f t h e p r o d u c t was c u t i n t o s m a l l p i e c e s and s t i r r e d i n 250 ml c y c l o h e x a n e a t room temperature f o r 60 h r . The i n s o l u b l e f r a c t i o n was s e p a r a t e d by f i l t e r i n g the s o l u t i o n t h r o u g h c h e e s e c l o t h . The c y c l o h e x a n e - s o l u b l e f r a c t i o n was r e c o v e r e d by d i s t i l l i n g t h e s o l v e n t i n vacuo and the polymer was d r i e d i n vacuo a t 40 C f o r 24 h r . XYLENE FRACTIONATION. A 5-6g p o r t i o n o f the p r o d u c t was c u t i n t o s m a l l p i e c e s and h e a t e d i n 200 ml r e f l u x i n g x y l e n e f o r 5 h r . The h o t s u s p e n s i o n was f i l t e r e d t h r o u g h c h e e s e c l o t h i n t o 800 ml a c e t o n e . The polymer a d h e r i n g t o the s i d e s o f t h e f l a s k and t h e s m a l l amount f i l ­ t e r e d from t h e s u s p e n s i o n were r e f l u x e d w i t h an a d d i t i o n a l 150 ml x y l e n e u n t i l complete s o l u t i o n was n o t e d and then p r e c i p i t a t e d i n acetone. The p r e c i p i t a t e combined f i l t r a t e s were d u a l polymer, a s w e l l a polyme y precipitation, d r i e d i n vacuo a t 140 C f o r 4 h r . The polymer r e c o v e r e d from the f i l t r a t e s was i d e n t i f i e d as F r a c t i o n I I . CHARACTERIZATION. The i n t r i n s i c v i s c o s i t y o f t h e s o l u b l e f r a c t i o n s was d e t e r m i n e d i n t o l u e n e a t 30 C. The ΜΑΗ c o n t e n t o f t h e s o l u b l e f r a c t i o n s was d e t e r m i n e d by h e a t i n g a 0.5-1.0g p o r t i o n i n r e f l u x i n g w a t e r - s a t u r a t e d x y l e n e f o r 1 h r and t i t r a t i n g t h e h o t s o l u t i o n w i t h 0.05N e t h a n o l i c Κ 0 Η u s i n g 1% thymol b l u e i n DMF a s i n d i c a t o r . RESULTS The [y] o f EPR d e c r e a s e d when mixed f o r 10 min i n a Brabender P l a s t i c o r d e r a t 180 C. The complete s o l u b i l i t y o f t h e EPR i n c y c l o h e x a n e a t 22 C was unchanged. The p r e s e n c e o f 0.25-0.5 wt-% DCP a t 180°C r e s u l t e d i n t h e f o r ­ m a t i o n o f about 20% o f a c y c l o h e x a n e - i n s o l u b l e f r a c t i o n . The p r e ­ sence o f 5 wt-% ΜΑΗ (based on EPR) i n c r e a s e d t h e amount o f c y c l o h e x ­ a n e — i n s o l u b l e g e l , whose c o n c e n t r a t i o n d e c r e a s e d from 65% t o 27% a s the DCP c o n t e n t i n c r e a s e d from 0.25 t o 1.0 wt-% (based on EPR), r e s ­ pectively. The c y c l o h e x a n e - s o l u b l e polymer c o n t a i n e d about 1 wt-% ΜΑΗ which a p p a r e n t l y i n c r e a s e d w h i l e t h e [rç] d e c r e a s e d as t h e DCP content i n c r e a s e d (Table I ) . When t h e DCP c o n c e n t r a t i o n was k e p t c o n s t a n t a t 1 wt-% w h i l e t h e ΜΑΗ c o n c e n t r a t i o n i n the c h a r g e i n c r e a s e d from 5 t o 20 wt-%, t h e amount o f c y c l o h e x a n e - i n s o l u b l e polymer d e c r e a s e d from 29 t o 23%. The o f t h e c y c l o h e x a n e - s o l u b l e polymer i n c r e a s e d and i t s ΜΑΗ c o n t e n t d e c r e a s e d , a s the ΜΑΗ c o n c e n t r a t i o n i n t h e c h a r g e i n c r e a s e d ( T a b l e I I ) . When s t e a r a m i d e (SA) was p r e s e n t i n t h e DCP-MAH m i x t u r e added t o EPR a t 180 C, t h e amount o f c y c l o h e x a n e - i n s o l u b l e EPR-g-MAH d e c r e a s e d , a n a l o g o u s t o t h e e f f e c t o f SA i n r e d u c i n g c r o s s l i n k i n g i n t h e PE-MAHp e r o x i d e r e a c t i o n ( 8 , 9 ) . The [η] o f t h e c y c l o h e x a n e - s o l u b l e EPR-g-MAH i n c r e a s e d when SA was p r e s e n t i n t h e r e a c t i o n m i x t u r e , a n a l o g o u s t o the e f f e c t o f SA i n r e d u c i n g d e g r a d a t i o n i n t h e PP-MAH-peroxide r e ­ a c t i o n (Table I I I ) .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

Table I .

E f f e c t o f DCP a t C o n s t a n t ΜΑΗ C o n c e n t r a t i o n a t 180°C C yc1ohexane E x t r a c t i o n

ΜΑΗ wt-% on EP

DCP wt-% on EP on ΜΑΗ

0 0 0

a

c

d

0 0.25 0.5

0 0 0

Soluble

[yi]

b

Insoluble

c

%

dl/g

100 77 80

1.20 1.42 1.23

a

ΜΑΗ wt-%

%

0 0 0

0 20 16

5 0.25 5 33 1.10 0.9 5 0.5 10 56 0.56 1.0 5 1^0 20 73 0.89 1^3 E x t r a c t i o n w i t h c y c l o h e x a n e a t 2 2 ^ f o r 60 h r R e c o v e r e d by s o l v e n t removal from f i l t r a t e T o l u e n e , 30°C U n t r e a t e d EPR fyj] 1.4 Table I I .

E f f e c t o f ΜΑΗ a t C o n s t a n t DCP C o n c e n t r a t i o n a t 180°C Cyclohexane

ΜΑΗ wt-% on EP

DCP wt-% on EP on ΜΑΗ

5 10 20 a,b,c

1.0 20 1.0 10 1.0 5 Footnotes t o Table I

T a b l e :I I I .

65 43 27

E f f e c t of

Soluble

Extraction

Insoluble

b

%

dl/g

ΜΑΗ wt-%

70 72 75

1.31 1.34 1.64

0.7 0.5 0.3

[71]°

Stearamide

3

% 29 26 23

i n EPR-MAH-DCΡ R e a c t i o n a t 180°C Cyclohexane E x t r a c t ! o n

ΜΑΗ wt-% on EP 5 5

DCP wt-% on EP on ΜΑΗ 0.25 0.25

5 5

5 0.5 10 5 0.5 10 a,£>,c F o o t n o t e s t o T a b l e I d

d

SA mole-% on ΜΑΗ

Soluble

a

Insoluble

b

%

dl/g

ΜΑΗ wt-%

0 20

33 43

1.10 1.18

0.9 0.5

65 55

0 20

56 68

0.56 1.02

1.0 1.6

43 29

%

SA-MAH-DCP m i x t u r e added i n 4 e q u a l p o r t i o n s t o m o l t e n EP

The polymer formed i n t h e r e a c t i o n o f EPR w i t h 0.5 wt-% DCP a t 180 C, i n t h e p r e s e n c e o r absence o f 5 wt-% Μ Α Η , was c o m p l e t e l y s o l ­ uble i n r e f l u x i n g xylene, although i t contained a f r a c t i o n i n s o l u b l e i n c y c l o h e x a n e a t 22 C. The EPR and EPR-g-MAH were f r a c t i o n a t e d by a d d i t i o n o f the xylene s o l u t i o n t o acetone. Both t h e a c e t o n e - p r e c i p i t a t e d polymer ( I ) and t h e polymer r e c o v ­ e r e d by removal o f t h e s o l v e n t from t h e a c e t o n e - x y l e n e f i l t r a t e ( I I ) had a h i g h e r [Ή] when ΜΑΗ was p r e s e n t i n t h e c h a r g e , a l t h o u g h t h e amount o f a c e t o n e - p r e c i p i t a t e d polymer ( I ) was d e c r e a s e d when ΜΑΗ had

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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Copolymer Rubber

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been p r e s e n t . The p r e s e n c e o f s t e a r a m i d e i n t h e EPR-MAH-DCP r e a c t i o n m i x t u r e i n c r e a s e d t h e amount and [yi] o f t h e acetone p r e c i p i t a t e d polymer ( T a b l e I V ) . T a b l e IV.

F r a c t i o n a t i o n o f EPR-MAH-DCP P r o d u c t i n X y l e n e Xylene

ΜΑΗ wt-% on EP

0 0 5 5

DCP SA CH wt-% mole-% I n s o l on EP on ΜΑΗ on ΜΑΗ %

0.0 0.5 0.5 0.5

0 0 10 10

0 0 0 20

0 16 43 29

Fractionation e

b

Fraction I * ΜΑΗ [>|] % d l / g wt-% r

82 85 48 68

2.44 1.17 1.38 1.71

0 0 1.9 1.2

a

0

e

Fraction I I [^] ΜΑΗ % d l / g wt-% £

15 15 46 28

0.60 0.37 1.23 0.94

0 0 2.9 2.7

a

EPR r e a c t i o n s c o n d u c t e d i n P l a s t i c o r d e r a t 180°C k E x t r a c t i o n with cyclohexan Extraction with r e f l u x i n F r a c t i o n I r e c o v e r e d by p r e c i p i t a t i n g x y l e n F r a c t i o n I I r e c o v e r e d by removal o f s o l v e n t from T o l u e n e , 30°C

c

d

e

filtrate

f

DISCUSSION The complete s o l u b i l i t y i n r e f l u x i n g x y l e n e o f t h e EPR and EPR-g-MAH produced by r e a c t i o n w i t h DCP a t 180°C s u g g e s t s t h a t t r e a t m e n t w i t h c y c l o h e x a n e a t 22°C does n o t s e p a r a t e t h e c r o s s l i n k e d polymer from the u n c r o s s l i n k e d polymer b u t r a t h e r f r a c t i o n a t e s t h e u n c r o s s l i n k e d polymer based on m o l e c u l a r w e i g h t . A l t e r n a t i v e l y , the l i g h t l y c r o s s l i n k e d polymer i s s w o l l e n and t h e c r o s s l i n k s a r e broken i n r e ­ f l u x i n g xylene. The c r o s s l i n k i n g o f EPR i n t h e p r e s e n c e o f r a d i c a l s from p e r o x i d e d e c o m p o s i t i o n i s a t t r i b u t a b l e t o a t t a c k on t h e s e c o n d a r y CH2 m o i e t i e s and t h e g e n e r a t i o n o f polymer r a d i c a l s which c o u p l e e i t h e r w i t h s i m i ­ l a r s e c o n d a r y polymer r a d i c a l s o r polymer r a d i c a l s g e n e r a t e d by a t t a c k on t h e t e r t i a r y CH m o i e t i e s on t h e p r o p y l e n e u n i t s i n t h e chain. The g e n e r a t i o n o f t e r t i a r y r a d i c a l s by t h e l a t t e r r o u t e i s t h e predominant r e a c t i o n . The t e r t i a r y r a d i c a l s p r e f e r e n t i a l l y undergo d i s p r o p o r t i o n a t i o n , r e s u l t i n g i n degradation r a t h e r than c r o s s l i n k i n g . I n c r e a s i n g t h e DCP c o n c e n t r a t i o n r e s u l t s i n an i n c r e a s e i n t h e amount o f s o l u b l e polymer a n d a d e c r e a s e i n t h e m o l e c u l a r weight o f t h e polymer due t o i n c r e a s e d t e r t i a r y CH a t t a c k , f o l l o w e d by d i s p r o p o r ­ tionation. The r a p i d d e c o m p o s i t i o n o f a p e r o x i d e i n t h e p r e s e n c e o f ΜΑΗ r e s u l t s i n t h e e x c i t a t i o n and h o m o p o l y m e r i z a t i o n o f ΜΑΗ. When t h e l a t t e r i s c o n d u c t e d i n t h e p r e s e n c e o f p o l y p r o p y l e n e , the l a t t e r undergoes d e g r a d a t i o n (10) w h i l e p o l y e t h y l e n e i s c r o s s l i n k e d under the same c o n d i t i o n s ( 1 1 ) . T h i s has been a t t r i b u t e d t o t h e p r e s e n c e o f e x c i t e d ΜΑΗ which i n c r e a s e s the r a d i c a l g e n e r a t i o n on t h e polymer beyond t h a t due t o t h e r a d i c a l s from t h e p e r o x i d e . A t a f i x e d ΜΑΗ c o n c e n t r a t i o n , i n c r e a s i n g t h e p e r o x i d e c o n t e n t r e s u l t s i n a h i g h e r c o n c e n t r a t i o n o f e x c i t e d ΜΑΗ and a g r e a t e r gen­ e r a t i o n o f polymer r a d i c a l s . The l a t t e r undergo d i s p r o p o r t i o n a t i o n and t h e amount o f s o l u b l e polymer i n c r e a s e s w h i l e i t s m o l e c u l a r weight decreases. Notwithstanding, a t a given peroxide concentration,

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CHEMICAL REACTIONS ON POLYMERS

the p r e s e n c e o f ΜΑΗ i n c r e a s e s t h e amount o f c y c l o h e x a n e - i n s o l u b l e polymer a p p r o x i m a t e l y t h r e e f o l d . A t a f i x e d DCP c o n c e n t r a t i o n , i n ­ c r e a s i n g t h e ΜΑΗ c o n t e n t has l i t t l e e f f e c t on t h e c o n c e n t r a t i o n o f e x c i t e d ΜΑΗ and t h e r e f o r e a n e g l i g i b l e e f f e c t on t h e amount o f s o l u b l e polymer. F u r t h e r , t h e ΜΑΗ c o n t e n t o f the polymer d e c r e a s e s w i t h an i n c r e a s e i n t h e amount o f ΜΑΗ i n t h e c h a r g e due t o t h e q u e n c h i n g o f e x c i t e d ΜΑΗ by e x c e s s ground s t a t e Μ Α Η . A l t h o u g h i t has been s u g g e s t e d t h a t c r o s s l i n k i n g i n t h e p r e s e n c e o f ΜΑΗ i n v o l v e s c o u p l i n g o f appended ΜΑΗ r a d i c a l s w i t h o t h e r appended ΜΑΗ r a d i c a l s o r w i t h polymer r a d i c a l s (7), the former i s i m p r o b a b l e due t o t h e tendency f o r d i s p r o p o r t i o n a t i o n r a t h e r t h a n c o u p l i n g between r a d i c a l s d e r i v e d from s t r o n g e l e c t r o n a c c e p t o r monomers s u c h as Μ Α Η . The i n c r e a s e d c r o s s l i n k i n g may be a t t r i b u t e d t o t h e p r e f e r e n t i a l g e n e r a t i o n o f s e c o n d a r y polymer r a d i c a l s due t o t h e p r e s e n c e o f e x c i t e d ΜΑΗ and t h e r e f o r e an i n c r e a s e i n t h e amount o f c o u p l i n g o f s e c o n d a r y polymer r a d i c a l Stearamide i s one o t r o n t o the c a t i o n i c moiety propagating c h a i n s . T h i s r e s u l t s i n t h e i n h i b i t i o n o f the h o m o p o l y m e r i z a t i o n o f ΜΑΗ and d e c r e a s e s t h e c r o s s l i n k i n g o f p o l y e t h y l e n e and the d e g r a d a ­ t i o n o f p o l y p r o p y l e n e which accompany t h e p e r o x i d e - c a t a l y z e d r e a c t i o n o f ΜΑΗ w i t h t h e s e p o l y o l e f i n s ( 8 , 9 ) . The p r e s e n c e o f s t e a r a m i d e i n t h e EPR-MAH-DCP r e a c t i o n i n c r e a s e s the y i e l d o f s o l u b l e polymer, i . e . d e c r e a s e s t h e c r o s s l i n k i n g , which polymer has a h i g h e r m o l e c u l a r w e i g h t , i . e . d e c r e a s e s t h e d e g r a d a t i o n , t h a n n o t e d i n t h e absence o f s t e a r a m i d e .

Literature Cited 1. Crespi, G.; Bruzzone, M. Chim. e Ind. (Milan) 1959, 41, 741. 2. Natta, G.; Crespi, G.; Bruzzone, M. Kautschuk u. Gummi 1961, 14 (3), WT54. 3. Natta, G.; Crespi, G.; Valvassori, A.; Sartori, G. Rubber Chem. Technol. 1963, 36, 1583. 4. Loan, L. D. J. Polym. Sci. 1964, A2, 3053. 5. Harpell, G. A.; Walrod, D. H. Rubber Chem. Technol. 1973, 46, 1007. 6. Lenas, L. P. Ind. Eng. Chem., Prod. Res. Dev. 1963, 2, 202. 7. Natta, G.; Crespi, G.; Borsini, G. (to Montecatini Soc. Gen.) U.S. Patent 3 236 917, 1966. 8. Gaylord, N. G. (to Gaylord Research Institute, Inc.) U.S. Patent 4 506 056, 1985. 9. Gaylord, N. G.; Mehta, R. Polymer Preprints 1985, 26 (1), 61. 10. Gaylord, N. G.; Mishra, M. K. J. Polym. Sci., Polym. Lett. Ed. 1983, 21, 23. 11. Gaylord, N. G.; Mehta, M. J. Polym. Sci., Polym. Lett. Ed. 1982, 20, 481. RECEIVED October

13, 1987

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

Chapter 32

Synthesis of Conjugated Polymers via Polymer Elimination Reactions Samson A. Jenekhe Physical Sciences Center, Honeywell, Inc., 1071 Lyndale Avenue, South Bloomington, MN 55420 The transformatio f nonconjugated polymer int conjugated polymer described. Heterocyclic conjugated polymers containing alternating aromatic and quinonoid sections in the main chain are synthesized by chemical or electrochemical redox elimination reaction on soluble precursor polymers containing sp -carbon atom bridges between the aromatic heterocyclic units. Progress of the redox elimination process is followed by infrared and electronic spectra as well as by cyclic voltammetry. A reaction mechanism in which the precursor polymer undergoes a redox reaction followed by loss of the bridge hydrogens is proposed. The resulting conjugated aromatic/quinonoid polymers generally have very small semiconductor band gaps in accord with predictions of recent theoretical calculations. A brief review of related syntheses of conjugated polymers from nonconjugated precursor polymers is also given. 3

Conjugated polymers are currently of wide interest because of their e l e c t r o n i c (1), electrochemical (2), and nonlinear o p t i c a l (3) properties which originate from their delocalized îi-electron systems. Unfortunately, the high density and geometrical d i s p o s i t i o n of π-bonds i n conjugated polymers which confine the desirable electronic and o p t i c a l properties also make them more insoluble and i n f u s i b l e r e l a t i v e to nonconjugated polymers. The many synthetic routes to conjugated polymers may be c l a s s i f i e d into two broad categories: (1) those i n which the target conjugated polymer i s obtained d i r e c t l y from conventional addition and condensation polymerization processes (4), and (2) those involving transformation of an existing nonconjugated precursor polymer into the target conjugated polymer (jj). The l a t t e r approach i s especially a t t r a c t i v e since the nonconjugated precursor polymer can be more readily processed into films and other forms p r i o r to conversion to the 0097-6156/88/0364-0443$06.00/0 © 1988 American Chemical Society

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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conjugated d e r i v a t i v e . Also, the nonconjugated precursor polymer route w i l l allow the tuning of physical properties of the conjugated derivative, including density, morphology, c r y s t a l l i n i t y , and electronic and o p t i c a l properties. Among the possible polymer reactions which could be used to convert nonconjugated polymers into conjugated ones are elimination, addition, and isomerization (5), but our primary interest here i s polymer elimination reactions. One of the e a r l i e s t known synthesis of a conjugated polymer by elimination on a nonconjugated precursor was achieved by Marvel et a l (6) who demonstrated that poly acetylene was obtained by elimination of HC1 from polyvinyl chloride as i l l u s t r a t e d i n Figure 1. Feast and h i s co-workers have recently described an elegant synthesis of polyacetylene (PA) films by thermal elimination of aromatic hydrocarbons such as 1,2-bis(trifluoromethyl)benzene, naphthalene and anthracene from films of soluble nonconjugated precursor polymers (7), Figure 2. The r e s u l t i n g polyacetylene films, now known i n the l i t e r a t u r e as Durham polyacetylene have physical properties that are s i g n i f i c a n t l polyacetylene: Durham P morphology compared to Shirakawa PA which i s highly c r y s t a l l i n e and fibrous (8-9). Also recently, Lenz, Karasz and co-workers (10) have reported the synthesis of poly(p-phenylenevinylene) (PPV) films by thermal elimination of ( G ^ ^ S and HC1 from poly (p-xylene-α-dime thy 1sulfonium c h l o r i d e ) , a soluble p o l y e l e c t r o l y t e (see Figure 3). Highly oriented Durham PA and PPV films with stretch r a t i o s up to 20 have been obtained by stretching the precursor polymer films during the transformation to conjugated derivatives; such oriented films when doped give r i s e to conductors with large anisotropy i n e l e c t r i c a l conductivity. The Durham route to polyacetylene and the above PPV synthesis demonstrate the r i c h potentials of synthesis of conjugated polymers v i a elimination reactions on nonconjugated precursor polymers. Recently, we discovered a novel type of polymer elimination reaction f o r producing conjugated polymers from the c l a s s of nonconjugated polymers containing a l t e r n a t i n g sp3-carbon atom (-C(R)H-) and conjugated sections i n the main chain (11-13). Under chemical or electrochemical oxidative or reductive conditions such polymers undergo i r r e v e r s i b l e reactions leading to loss of the bridge hydrogens, converting the sp3-carbon to sp2-carbon as i l l u s t r a t e d i n Figure 4, where D or A denotes π-electron donor or acceptor conjugated sections. I n i t i a l observations on this redox elimination reaction were made on poly(3,6-N-methylcarbazolediyl methylene) (PMCZM) (11) and poly(3,6-N-methylcarbazolediyl benzylidene) (PMCZB) (12). For example, upon oxidation of PMCZM and PMCZB with bromine or iodine i t was shown that a bridge hydrogen was eliminated as HBr or HI r e s u l t i n g i n f u l l y conjugated doped derivatives which had dc conductivities (0.1-1 S/cm) as high as the parent poly(3,6-Nmethylcarbazolediyl) (11-12). Figure 5 shows the o p t i c a l absorption spectra of a f i l m of PMCZM before and a f t e r a prolonged exposure to iodine vapor. The large red s h i f t , corresponding to a narrowing of the o p t i c a l band gap or increase i n the degree of conjugation i s to be noted. Also, i t i s s i g n i f i c a n t that elimination of the bridge hydrogens (-C(R)H-) i n PMCZM and PMZCB produced conjugated polymers containing quinonoid sections i n the main chain. These i n i t i a l

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

32.

JENEKHE

Figure 1.

Figure 2.

Synthesis of Conjugated Polymers

Synthesis of polyacetylene by elimination of HC1.

from p o l y v i n y l chloride

The soluble nonconjugated precursor polymer route to Durham polyacetylene v i a thermal elimination.

H C

PH

3

H +S _ , r

c—c I H

Figure 3.

445

I

H

Synthesis of poly(p-phenylene vinylene) films by thermal elimination on a soluble p o l y e l e c t r o l y t e .

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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446

SCHEME 2

SCHEME 1

—\

H I

DORA

DORA

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Redox

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R

F i g u r e 4.

R

G e n e r a l scheme o f i r r e v e r s i b l e redox e l i m i n a t i o n r e a c t i o n on t h e c l a s s o f nonconjugated polymers c o n t a i n i n g a l t e r n a t i n g -C(R)H- and c o n j u g a t e d s e c t i o n s i n t h e main c h a i n y i e l d i n g c o n j u g a t e d polymers.

CH

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, θ 3

LUndopedPMCZM 2.l dopedPMCZM

Φ 1.2

υ c

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200

600

1100

1600

*

2100

2500

wavelength (nm)

F i g u r e 5.

O p t i c a l absorption spectra of a t h i n f i l m of p r e c u r s o r PMCZM ( 1 ) and a f t e r exposure t o i o d i n e v a p o r ( 2 ) . A l s o shown i s t h e proposed scheme o f redox e l i m i n a t i o n y i e l d i n g a doped c o n j u g a t e d c o n d u c t i n g polymer.

J

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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observations lead us to pursue the synthesis of conjugated polymers containing alternating aromatic and quinonoid sequences i n the main chain v i a redox elimination on precursors, such as the heterocyclic conjugated polymers of Figure 6. Extensive recent theoretical calculations predict that very narrow band gaps would be obtained i n conjugated polymers containing quinonoid sections (14-18). We recently reported the smallest bandgap i n organic polymers f o r such conjugated polymers (19). In this paper we present r e s u l t s on the polymer redox elimination reaction used i n the synthesis of the polymers i n Figure 6. Preliminary results on electrochemical redox elimination on precursor polymers are also presented. A mechanism of the polymer elimination reaction i s proposed. Related recent experimental observations at other laboratories that can be described within the framework of the scheme of Figure 4 are discussed. Experimental Precursor Polymers. Th synthesi nonconjugated precursor polymers containing alternating heteroaromatic units and -C(R)H- i n the main chain are described elsewhere (20-21). These nonconjugated precursor polymers include polythiophenes, polypyrroles and polyfurans; however, only the studies done with some of the polythiophenes and their related conjugated derivatives are described i n d e t a i l here: poly(2,5thiophenediyl benzylidene) (PTB), poly[ a-(5,5'-bithiophenediyl) benzylidene] (PBTB), poly[ a-(5-5 -bithiophenediyl)pacetoxybenzylidene] (PBTAB), and poly[a-(5-5"-terthiophenediyl) benzylidene] (PTTB). These precursor polymers are soluble i n organic solvents including tetrahydrofuran (THF), methylene chloride and Ν,Ν-dimethylformamide (DMF). Thin films used i n spectroscopy and for c y c l i c voltammetry were cast from THF, methylene chloride or DMF. f

Elimination Procedures. Chemical redox-induced elimination was performed on precursor thin films by exposure to bromine or iodine vapor or by immersion of films i n hexane solutions of these halides. In order to follow progress of elimination, reactions were also performed on thin films i n a special sealed glass c e l l which permitted i n s i t u monitoring of the electronic or infrared spectra at room temperature (23°C). T y p i c a l l y , the infrared or electronic spectrum of the p r i s t i n e precursor polymer f i l m was obtained and then bromide vapor was introduced into the reaction v e s s e l . In s i t u FTIR spectra i n the 250-4000 cm"* region were recorded every 90 sec with a D i g i l a b Model FTS-14 spectrometer and o p t i c a l absorption spectra i n the 185-3200 nm (0.39-6.70 eV) range were recorded every 15 min with a Perkin-Elmer Model Lambda 9 UV-vis-NIR spectrophotometer. The reactions were continued u n t i l no v i s i b l e changes were detected i n the spectra. C y c l i c voltammetry was performed on precursor polymer thin films cast on platinum electrodes i n order to assess the p o s s i b i l i t y of electrochemical redox elimination and consequently as an alternative means of monitoring the process. A l l electrochemical experiments were performed i n a three-electrode, single-compartment c e l l using a double junction Ag/Ag (AgN03) reference electrode i n 0.1M +

American Chemical Society, Library 1155 16th St., N.W. In Chemical Reactions on Polymers; Washington, OX. Benham, 20036J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

tetraethylammonium perchlorate (TEAP)/acetonitrile. The voltage regulator was a Princeton Applied Research Model 175 Universal programmer. Current measurement was done using a Princeton Applied Research Model 173 Potentiostat/Galvanostat i n conjunction with Princeton Applied Research Model 376 logarithmic current converter. The c y c l i c voltammograms were recorded on a HP Model 7040A X-Y recorder. Results Figure 7 shows the FTIR spectra of i n i t i a l precursor PBTB f i l m (A) and at two subsequent times (B and C) during i n s i t u elimination reaction with bromine vapor at 23°C. Several main changes i n the infrared spectrum of the precursor f i l m are observed. The a l i p h a t i c C-H stretching v i b r a t i o n bands i n the 2800-3000 cm~l region attributed to the bridge sp3 C-H are s i g n i f i c a n t l y modified, generally decreasing with elimination reaction time and eventually disappearing. In contrast cm-1 region attributed remain r e l a t i v e l y the same. A new gas phase absorption band at 2400-2800 cm"l assigned to evolved HBr gas appears as seen i n Figure 7 (B and C). The gas phase absorption band attributed to HBr gas appeared i n the f i r s t spectrum a f t e r bromine was introduced into the reaction c e l l and i n t e n s i f i e d with reaction time. New absorption bands appeared and intensity of e x i s t i n g ones increased i n the carbon-carbon double bond absorption region, 1000-1600 c n r l . There was no evidence of a new band i n the 500-650 cm~l region that would be a t t r i b u t a b l e to a C-Br bond due to substitution or bromination reactions on the polymer chain. These IR spectra r e s u l t s c l e a r l y show that the bridge hydrogens (-C(R)H-) of PBTB are eliminated as HBr by reaction with bromine, y i e l d i n g the anticipated aromatic/ quinonoid conjugated polymers of Figure 6. The e l e c t r o n i c absorption spectra at d i f f e r e n t times of elimination reaction on PBTB are shown i n Figure 8. As-synthesized PBTB i s a green polymer (Curve 1, Figure 8) due to p a r t i a l conversion of the -C(R)H- to -C(R)= bridges i n the main chain (19-21). A f t e r 15 min. reaction time, the e l e c t r o n i c spectrum i s greatly red-shifted with the absorption edge now located at about 1200 nm (1.03 eV). Progress i n elimination further moves the absorption edge to longer wavelength as curves 2 to 13 i n Figure 8 show. No observable changes i n the e l e c t r o n i c absorption spectra were seen a f t e r 24 hours (Curve 13). V i s u a l l y , the sample changes from green (Curve 1) to m e t a l l i c gray i n c o l o r . The absorption edge determined from Curve 13 i s about 1500 nm (0.83 eV). This represents an extremely large increase i n the degree of ττ-electron d e l o c a l i z a t i o n . The r e l a t i v e l y sharp absorption edges are also noteworthy. Figure 9 shows the e l e c t r o n i c absorption spectrum of a PTTB f i l m which has undergone extensive but incomplete reaction with bromine i n a non-in-situ experiment. The absorption spectrum i s that expected f o r a one-dimensional conjugated polymer. The sharpest absorption edge i s a t about 1490 nm (o.83 eV) and the absorption maximum i s located at 1240 nm (1.0 eV). Thus, this material has a bandgap of about 0.83 eV. Note that two small

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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R

Ill—

Figure 6.

3600

Novel conjugated heteroaromatic by redox elimination.

3200

2800

2400

2000

1600

polymers synthesized

1200

800

400

Wavenumbers (cm ~ ) 1

Figure 7.

FTIR absorption spectra of precursor PBTB thin f i l m (A) and during i n - s i t u elimination (B and C) i n bromine vapor at 23°C. Arrow indicates a superposed gas phase absorption band due to evolved HBr gas.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

ι

ι

600

1000

01 200

ι 1400

ι

ι

ι

1

1800

2200

2600

2800

Wavelength (nm)

F i g u r e 8.

E l e c t r o n i c a b s o r p t i o n s p e c t r a o f p r e c u r s o r PBTB t h i n f i l m ( 1 ) and c o n j u g a t e d d e r i v a t i v e s (2-13) a t d i f f e r e n t times d u r i n g i n - s i t u e l i m i n a t i o n r e a c t i o n a t 23°C.

1.50

Ο 0.0

'

200

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'

1

1

600

'

1

'

1

'

1000

'

'

1

'

1400

'

L—J

1

ι i—• 1 ι ι ' 1

1800

2200

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2600

Wavelength (nm)

F i g u r e 9.

E l e c t r o n i c absorption spectra of a conjugated derivative of ΡΠΒ.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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451

absorptions can be seen below the gap at 1560 nm (0.79 eV) and 1950 nm (0.64 eV). The two absorptions below the bandgap may be interpreted as evidence of charged bipolarons (dications) (22). However, no such below bandgap absorptions are observed i n the completely reacted material. Some of the results of c y c l i c voltammetrie studies of a f i l m of PBTAB at various stages of redox elimination are shown i n Figures 10A and 10B. The c y c l i c voltammogram of Figure 10A shows the behavior of a precursor PBTAB f i l m on platinum electrode under repeated c y c l i n g at 200mV/s. I n i t i a l l y , an oxidation peak at about 0 V (vs. Ag/Ag ), a main reduction peak at -0.56 V and a small broad reduction peak centered at -0.15 V are observed. This i n i t i a l votammogram i s very unstable under c y c l i n g : ( i ) the redox peaks at -0.56 V and 0.0 V are decreasing; and ( i i ) evolving very broad peaks that form a redox couple are observed i n the range +0.14-0.21 and -0.09 to -0.23 V. After numerous c y c l i n g (-100) over a period of hours the r e s u l t i n g polyme f i l washed d i t cycli voltammogram was again obtaine redox couple with oxidatio -0.24 V was obtained as shown i n Figure 10B. This l a t e r c y c l i c voltammogram i s quite stable under repeated c y c l i n g and i s what one might expect for an electroactive conjugated polymer. These results suggest that the electrochemical redox reaction induces elimination of the -C(R)H- bridge hydrogens, y i e l d i n g -C(R)= bridges. Preliminary measurements of e l e c t r i c a l conductivity of the conjugated derivatives of PBTAB, PBTB and PTTB obtained by the above treatment with bromine vapor are poor semiconductors with a conductivity of the order 10"^S/cm which apparently i s not due to doping. Subsequent electrochemical or chemical doping of these polymers lead to 4-6 orders of magnitude increase i n conductivity. Ongoing studies of the e l e c t r i c a l properties of these conjugated polymers with alternating aromatic/quinonoid units w i l l be reported elsewhere. Similar redox elimination reactions have been performed on several heteroaromatic precursor polymers within the class shown i n Figure 4 and whose conjugated derivatives are shown i n Figure 6. In general, the r e s u l t s and observations are similar to those described here. The major differences observed are due to differences i n the heteroatom (X) while minor differences are observed with d i f f e r e n t R groups. For example, the smallest bandgaps were obtained when X=S i n the polymers of Figure 6. On the other hand, faster elimination k i n e t i c s were observed for aromatic R compared to a l i p h a t i c R side groups. +

Discussion The electronic absorption spectra of Figures 8 and 9, and those not shown, reveal that the conjugated polymers of Figure 6 generally exhibit i n t r i n s i c semiconductor bandgaps that are very small. This i s i n accord with extensive recent theoretical calculations which predict that introduction of quinoidal geometry into the main chain of aromatic conjugated polymers (e.g. polythiophene, polypyrrole, and poly-p-phenylene) reduces the bandgap. E s p e c i a l l y relevant are the

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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CHEMICAL REACTIONS ON POLYMERS

F i g u r e 10A.

C y c l i c voltammogram o f a p r e c u r s o r PBTAB t h i n f i l m on P t e l e c t r o d e i n T E A P / a c e t o n i t r i l e a t a scan r a t e o f 200 mV/s.

F i g u r e 10B.

C y c l i c voltammogram o f t h e same f i l m i n F i g u r e 10A o b t a i n e d a f t e r washing and r u n n i n g i n a f r e s h TEAP/ a c e t o n i t r i l e a t a scan r a t e o f 200 mV/s.

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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valence e f f e c t i v e hamiltonian (VEH) calculations of Bredas and co-workers (14-16) which are known to be very accurate i n reproducing experimental data for conjugated polymers. In p a r t i c u l a r , Bredas has shown that as quinonoid structure i s introduced into poly(2,5thiophene) geometry the bandgap decreases l i n e a r l y with increasing quinonoid character (14). More recently, the electronic band structures of the aromatic/quinonoid polymers of Figure 6 have been obtained using MNDO polymer geometry optimized t o t a l energy calculations (23). The theoretical energy bandgaps (23) were found to be i n agreement with the experimental results (19"T7 Mechanism of Redox Elimination. The proposed elimination reaction mechanism i s i l l u s t r a t e d with a methylene-bridged polybithiophene i n Figure 11. I f one considers attempts to oxidize the nonconjugated precursor polymer by electron withdrawal or reduce i t by electron addition, one finds that the added charge cannot be accommodated by d e r e a l i z a t i o n because of th 3 hybridized carbo (-CH2-) bridges Consequently, highly unstabl Depending on the sign o high energy unstable intermediate would be best s t a b i l i z e d by loss of HÎ or H" from adjacent bridges, y i e l d i n g the neutral conjugated polymer chain containing alternating aromatic and quinoidal units. This mechanism can be used to explain the electrochemical r e s u l t s . For example, the observed decreasing redox peaks i n the c y c l i c voltammogram of Figure 10A i s attributed to the consumption of the charged intermediates. The optical, absorption data of Figure 9 also appear to evidence bipolarons (dications) as intermediate and hence, consistent with this mechanism. The general scheme of Figure 11 i s f o r both electrochemical and chemical redox elimination. I f we consider the case of oxidative elimination with bromine, generation of the necessary r a d i c a l cation or d i c a t i o n intermediate i s due to: B ^ + 2e" >2Br". The bromide ions presumably then abstract protons from the ionized precursor. Related Polymer Systems and Synthetic Methods. Figure 12A shows a hypothetical synthesis of poly (p-phenylene methide) (PPM) from polybenzyl by redox-induced elimination. In p r i n c i p l e , i t should be possible to accomplish t h i s experimentally under s i m i l a r chemical and electrochemical redox conditions as those used here for the related polythiophenes. The electronic properties of PPM have recently been theoretically calculated by Boudreaux et a l (16), including: bandgap (1.17 eV); bandwidth (0.44 eV); ionization p o t e n t i a l (4.2 eV); electron a f f i n i t y (3.03 eV); oxidation potential (-0.20 vs SCE); reduction p o t e n t i a l (-1.37 eV vs SCE). PPM has recently been synthesized and doped to a semiconductor (24). The two l i m i t i n g s t r u c t u r a l forms of p o l y a n i l i n e are shown i n Figure 12B: ( i ) the nonconjugated leuco base polymer i n which the imine nitrogens are completely protonated (PAN-1); and ( i i ) the neutral conjugated polymer containing alternating aromatic and quinoidal units (PAN-2). The highly conducting (10 S/cm) p o l y a n i l i n e chemically or electrochemically synthesized from a n i l i n e i s believed to be a p a r t i a l l y oxidized form with a structure intermediated between PAN-1 and PAN-2 (25-28). The complicated electrochemical behavior of polyaniline, especially i n aqueous media, i s a r e s u l t of redox reactions coupled with reversible deprOtonation/

In Chemical Reactions on Polymers; Benham, J., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1988.

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Figure 1 1 .

I l l u s t r a t i o n of the proposed mechanism of redoxinduced elimination.

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