Ring-Opening Polymerization. Kinetics, Mechanisms, and Synthesis 9780841209268, 9780841211162, 0-8412-0926-X

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Ring-Opening Polymerization. Kinetics, Mechanisms, and Synthesis
 9780841209268, 9780841211162, 0-8412-0926-X

Table of contents :
Title Page......Page 1
Half Title Page......Page 3
Copyright......Page 4
ACS Symposium Series......Page 5
FOREWORD......Page 6
PdftkEmptyString......Page 0
PREFACE......Page 7
1 Ring-Opening Polymerization: Introduction......Page 8
Thermodynamic Considerations......Page 11
Kinetic and Mechanistic Overview......Page 13
References......Page 27
2 Anionic Polymerization of Cyclosiloxanes with Cryptates as Counterions......Page 30
Anionic Polymerization of D3......Page 31
Anionic Polymerization of D4......Page 36
Molecular Weight Distributions of PDMS......Page 40
Literature Cited......Page 41
3 Anionic Polymerization of Ethylene Oxide with Lithium Catalysts Solution Properties of Styrene-Ethylene Oxide Block Polymers......Page 43
Experimental......Page 44
Results and Discussion......Page 45
Literature Cited......Page 50
4 Free Radical Ring-Opening Polymerization......Page 52
Free Radical Ring-Opening of Cyclic Ketene Acetals......Page 54
Nitrogen and Sulfur Analogs of Cyclic Ketene Acetals......Page 57
Ring-Opening Polymerization of Cyclic Vinyl Ethers......Page 58
Double Ring-Opening in Free Radical Polymerization......Page 62
Copolymerization with Cyclic Ketene Acetals......Page 64
Synthesis of Biodegradable Addition Polymers......Page 65
Ketene Acetals as New Chain Transfer Agents......Page 66
Acknowledgments......Page 67
Literature Cited......Page 68
5 Mechanism of N-Carboxy Anhydride Polymerization......Page 71
Background and Critique......Page 72
Acid-base Considerations......Page 77
Kinetic Considerations......Page 78
Concerning the Analogy Between the "a.m." Mechanism for NCA Polymerization and The Mechanism for The Anionic Polymerization of Lactams.......Page 80
Role of Self-Condensation Reactions......Page 81
The Carbamate Ion Mechanism as a Viable Alternative......Page 86
Literature Cited......Page 87
6 Ring-Opening Polymerization in the Synthesis of Block Copolymers......Page 90
Transformation Reactions......Page 91
Anion to Cation......Page 92
Cation to Anion......Page 93
Cation to Free Radical......Page 94
Reactions of Living Anionic Polymers With Living Poly THF......Page 95
Block Copolymers With Ionic Linking Groups......Page 96
Literature Cited......Page 97
7 Metal-Alcoholate Initiators Sources of Questions and Answers in Ring-Opening Polymerization of Heterocyclic Monomers......Page 99
Synthesis and properties of active μ-oxo-bimetallic alkoxides......Page 100
Polymerization of oxiranes......Page 101
Polymerization of other monomers......Page 104
Literature Cited......Page 105
8 Solvent and Substituent Effects in the Anionic Polymerization of α,α-Disubstituted β-Propiolactones......Page 107
Results and Discussion......Page 109
Experimental......Page 117
Literature Cited......Page 118
9 Structure-Reactivity Relationships in Ring-Opening Polymerization......Page 119
Determination of the chemical structures of the growing species......Page 120
Isomerism of the ionic active centers......Page 123
Covalent growing species......Page 124
Macroion-pairs and macroions......Page 126
Macroions and macroion-pairs in propagation......Page 129
Solvation phenomena......Page 130
Correlation of the structures and reactivities......Page 132
Literature Cited......Page 135
10 Control of Ring-Opening Polymerization with Metalloporphyrin Catalysts Mechanistic Aspects......Page 138
Structure and Reactivity of Growing Species in the Polymerization of Epoxide......Page 139
Copolymerization of Epoxide with CO2, and Epoxide with Cyclic Acid Anhydride......Page 141
Catalytic Reaction on Both Sides of a Metalloporphyrin Plane......Page 143
Literature Cited......Page 147
11 Anionic Ring-Opening Polymerization of Octamethylcyclotetrasiloxane in the Presence of 1,3-Bis(aminopropyl)-1,1,3,3-tetramethyldisiloxane......Page 148
A. Catalyst Preparation......Page 153
D. Capillary Gas Chromatography......Page 154
Results and Discussion......Page 155
Conclusions......Page 158
Literature Cited......Page 161
12 An Improved Process for є-Caprolactone-Containing Block Polymers......Page 162
Results and Discussion......Page 164
Conclusions......Page 171
Literature Cited......Page 174
13 Organolithium Polymerization of є-Caprolactone......Page 175
Results and Discussion......Page 176
Effect of Terminating Agent......Page 178
Literature Cited......Page 182
14 Cationic Heterocyclic Polymerization......Page 183
Mechanism and Kinetics......Page 184
Results and Discussion......Page 185
Cyclic Acetal Polymerization......Page 189
Grafting onto Experiments......Page 191
Literature Cited......Page 193
15 Thermally or Photochemically Induced Cationic Polymerization......Page 195
Photoinitiated Cationic Polymerization......Page 196
Thermally Initiated Cationic Polymerization......Page 197
Literature Cited......Page 203
Polymerization of Styrene Oxide......Page 205
Anionic Polymerization by Sodium Methoxide Catalyst......Page 207
Polymerization by Aluminum Alkoxides Catalyst......Page 209
Polymerization by ZnEt2/H2O Catalyst......Page 211
Controlled Polymerization of Oxiranes......Page 212
Polymerization of Epoxy Aldehydes and Derived Oxacyclic Monomers......Page 213
Literature Cited......Page 217
Results and Discussion......Page 218
Literature Cited......Page 228
18 Block Copolymer of Poly(ethylene glycol) and Poly(N-isovalerylethylenimine) Kinetics of Initiation......Page 229
Experimental......Page 230
Results......Page 231
Literature Cited......Page 240
19 Synthesis and Applications of Polysiloxane Macromers......Page 242
Preparation and Characterization of Polysiloxane Graft Copolymers......Page 243
Preparation and Characterization of Polysiloxane Macromers and Oligosiloxane Monomers......Page 246
Literature Cited......Page 257
20 Homopolymerization of Epoxides in the Presence of Fluorinated Carbon Acids Catalyst Transformations......Page 259
Results and Discussion......Page 260
Conclusions......Page 268
Literature Cited......Page 270
21 Mechanism of Ring-Opening Polymerization of Bicycloalkenes by Metathesis Catalysts......Page 271
Mechanistic Framework......Page 272
Cis Content......Page 273
Cis/Trans Distribution; Blockiness......Page 276
Head-tail Bias in Polymers of Asymmetric Monomers......Page 280
Tacticity......Page 283
Literature Cited......Page 287
22 Electrophilic Ring-Opening Polymerization of New Cyclic Trivalent Phosphorus Compounds A Novel Mechanism of Ionic Polymerization......Page 289
2-Phenyl-1,2-oxaphospholane (1)......Page 291
1-Phenyl-3H-2,1-benzoxaphosphole (2)......Page 296
Ionic Polymerization......Page 303
2-Phenyl-1,2-thiaphospholane(4) and 2-Phenyl-1,2-thiaphosphorinane(5)......Page 304
2-Phenyl-1,3,2-dioxaphosphepane(6)......Page 306
Literature Cited......Page 307
23 Synthesis and Polymerization of Atom-Bridged Bicyclic Acetals and Ortho Esters A Dioxacarbenium Ion Mechanism for Ortho Ester Polymerization......Page 309
Bicyclic Acetals: Synthesis......Page 310
Acid Hydrolysis of Bicyclic Acetals......Page 311
Polymerization of Bicyclic Acetals......Page 312
Bicyclic Orthoesters: Synthesis......Page 314
Polymerization of Bicyclic Orthoesters......Page 317
Conclusion......Page 324
Experimental of Bicyclic Orthoesters Mechanism Studies......Page 325
Literature Cited......Page 328
24 Radiation-Induced Cationic Polymerization of Limonene Oxide, α-Pinene Oxide, and β-Pinene Oxide......Page 330
Experimental......Page 331
Kinetic Characteristics of Polymerization......Page 332
1H-NMR Studies......Page 336
13C-NMR Studies......Page 343
Discussion......Page 347
Literature Cited......Page 352
25 Cationic Ring-Opening Polymerization of Epichlorohydrin in the Presence of Ethylene Glycol......Page 355
Results and Discussion......Page 356
Polymerization Mechanism......Page 360
Polyepichlorohydrin Polyols......Page 363
Experimental......Page 364
Literature Cited......Page 366
26 Lactone Polymerization Pivalolactone and Related Lactones......Page 367
Polymerization Mechanism......Page 369
Pivalolactone Polymers......Page 372
Block Copolymers......Page 373
Literature Cited......Page 378
Author Index......Page 380
A......Page 381
B......Page 382
C......Page 383
D......Page 384
E......Page 385
M......Page 386
P......Page 387
T......Page 389
X......Page 390

Citation preview

Ring-Opening Polymerization

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

ACS

SYMPOSIUM

SERIES

286

Ring-Opening Polymerization Kinetics, Mechanisms, and Synthesis James E. McGrath, EDITOR

Developed from a symposium sponsored by the Division of Polymer Chemistry at the 187th Meeting of the American Chemical Society, St. Louis, Missouri, April 8-13, 1984

American Chemical Society, Washington, D.C. 1985

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

Library of Congress Cataloging in Publication Data Ring-opening polymerization. (ACS symposium series, ISSN 0097-6156; 286) "Developed from a symposium sponsored by the Division of Polymer Chemistry at the 187th Meeting of the American Chemical Society, St. Louis, Missouri, April 8-13, 1984." Bibliography: p. Includes indexes. 1. Polymers and polymerization—Congresses. I. McGrath, James Ε. II. America Chemical Society. Division of Polymer Chemistry Chemical Society. Meeting (187th Mo.) IV. Series. QD380.R56 1985 ISBN 0-8412-0926-X

547.7

85-13352

Copyright © 1985 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, MA 01970, for copying beyond that permitted by Sections 107 or 108 of the U.S. 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. P R I N T E D IN THE U N I T E D STATES O F A M E R I C A

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

ACS Symposium Series M. Joan Comstock, Series Editor Advisory Board Robert Baker

Robert Ory

U.S. Geological Survey

Martin L. Gorbaty Exxon Research and Engineering C o .

Roland F. Hirsch U.S. Department of Energy

Geoffrey D. Parfitt Carnegie-Mellon University

James C. Randall Phillips Petroleum Company

Herbert D. Kaesz

Charles N. Satterfield

University of California—Los Angeles

Massachusetts Institute of Technology

Rudolph J. Marcus

W. D. Shults

Office of Naval Research

Oak Ridge National Laboratory

Vincent D. McGinniss Battelle Columbus Laboratories

Donald E. Moreland

Charles S. Tuesday General Motors Research Laboratory

Douglas B. Walters

U S D A , Agricultural Research Service

National Institute of Environmental Health

W. H. Norton

C. Grant Willson

J. T. Baker Chemical Company

I B M Research Department

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

FOREWORD T h e A C S S Y M P O S I U M S E R I E S was founded i n 1974 to provide a

m e d i u m for p u b l i s h i n g s y m p o s i a q u i c k l y i n b o o k form. T h e format o f the Series parallels that o f the c o n t i n u i n g A D V A N C E S IN C H E M I S T R Y S E R I E S except that, i n order to save time, the papers are not typeset but are reproduced as they are submitted by the authors i n camera-ready f o r m . Papers are reviewed under the supervision o f the E d i t o r s w i t h the assistance o f the Series A d v i s o r y B o a r d a n d are selected to m a i n t a i n the integrity o f the symposia; however, verbatim reproductions o f previously pub­ lished papers are not accepted. B o t h reviews a n d reports o f research are acceptable types o f presentation

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

PREFACE P O L Y M E R I Z A T I O N R E A C T I O N S C A N B E E A S I L Y C L A S S I F I E D i n t o either step-

g r o w t h (polycondensation) o r chain-reaction (addition) polymerizations. I n the latter type, the reaction mechanisms that can be considered depend u p o n the p o l y m e r i z a t i o n conditions a n d the structure o f the m o n o m e r . A l t h o u g h researchers have investigated m a n y types o f p o l y m e r i z a t i o n s , r i n g - o p e n i n g polymerizations, important fo

hav

bee

relativel

neglected

These p o l y m e r i z a t i o n s c a reaction; the distinction is often a function o f h o w molecular weight varies w i t h c o n v e r s i o n . P o l y m e r s o b t a i n e d b y r i n g - o p e n i n g p o l y m e r i z a t i o n s have already f o u n d m a n y important applications i n industry. These applications range f r o m water-soluble materials that are useful as o i l additives o r i n cosmetics t o reactive intermediates f o r segmented urethane o r urea foams a n d high-performance elastomers. M o r e o v e r , carpet fiber textile materials a n d significant new biomaterials are also often based

o n ring-opening

polymerization. T h e s y m p o s i u m u p o n w h i c h this b o o k is based p r o v i d e d a comprehen­ sive d i s c u s s i o n o f r i n g - o p e n i n g p o l y m e r i z a t i o n s ; presentations

b y 12

international speakers were included i n the 4-day sessions. T h u s , the chapters contained w i t h i n this b o o k s h o u l d represent a n up-to-date view o f the entire field

o f r i n g - o p e n i n g p o l y m e r i z a t i o n s . T h e ideas discussed a n d results

tabulated herein s h o u l d p r o v i d e the basis f o r m a n y a d d i t i o n a l academic experiments as well as industrial research a n d product development i n this important area. JAMES E . MCGRATH

Blacksburg, Virginia January, 1985

ix

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

1 Ring-Opening Polymerization: Introduction JAMES E. McGRATH Department of Chemistry and Polymer Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

The principal purpose of this paper is to provide a suitable intro­ duction to the remaining 25 papers that comprise this book. As mentioned earlier in the Preface this book is a result of a symposium presented in Division of the America the symposium have chosen to prepare manuscripts to further illustrate the research conducted in their own laboratories. A minority of these speakers chose to publish their work elsewhere. We have in fact been able to publish 26 of the 32 lectures which represents a substantial majority of those presented at the meeting. The range of topics discussed is quite broad and therefore should be of considerable interest to many scientists and engineers in both academic and industrial institutions around the world. The subjects include fundamental and applied research on the polymerization of cyclic ethers, siloxanes, N-carboxy anhydrides, lactones, heterocyclics, aziridines, phosphorous containing monomers, cycloalkenes, and acetals. Block copolymers are also discussed where one of the constituents is a ring opening monomer. Important new discussions of catalysis via not only the traditional anionic, cationic and coordination methods, but related UV initiated reactions and novel free radical mechanisms for ring opening polymerization are also included. It will be appropriate here to cite pioneering work in establishing a number of the fundamental thermodynamic and kinetic features associated with polymerization in general and ring opening reactions in particular (1-35). Fortunately, Professor Ivin along with Professor Saegusa have recently edited an excellent three­ -volumetreatise on ring opening polymerization (1). In this book, various experts in their own areas have contributed quite defini­ tive chapters on a number of the important polymerization aspects related to ring opening reactions. The book thus provides an ex­ cellent survey of the state-of-the-art and many references up through 1980 or perhaps later are included. Their important review should thus be very complementary to the current book which should be considered as more of a effort directed toward new research in ring opening polymerization reactions. However, the availability of 0097-6156/ 85/0286-0001 $06.50/ 0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

2

the Ivin/Saegusa book w i l l be u t i l i z e d i n this introductory a r t i c l e to i l l u s t r a t e a number of key points. Ring opening polymerizations have led to a number of com­ mercially important materials, some of which are i l l u s t r a t e d i n Scheme I. For example, polyoxymethylene i s an important a r t i c l e of commerce which can be prepared by the cationic ring opening of trioxane X to y i e l d the oxymethylene unit. In practice, these materials are copolymers with minor amounts of ethylene oxide included to s t a b i l i z e the macromolecule end groups. The polymeri­ zation of ethylene oxide 3 to y i e l d polyethylene oxide i s an example of the synthesis of an important water soluble macromolecule. Structure 4 currently produced at both low molecular weights of a few hundred to a few thousand, as well as i n very high molecular weight, e.g. up into the millions (25). The closely related polypropylene oxide i s an important intermediate for polyurethane foams and the production of nearly a l l of the automobile seating i n the United State ethers, based on tetrahydrofura oxonium ion methods to y i e l d polytetramethylene oxide 6 (PTMO). Ordinarily this material i s generated with dihydroxy end-groups and i s an important intermediate, not only for thermoplastic segmented polyurethanes and ureas but also for the thermoplastic polyester ether elastomers based upon polybutylene terephthalate and PTMO. Lactones, such as ε-caprolactone, were one of the e a r l i e s t ring opening polymerizations studied by Carothers some 50 years ago (1). At that point, i t was demonstrated that the low melting behavior (Tm ~50°C) observed with this polymer meant that 8 would not be of interest as a f i b e r . Relatively l i t t l e further work was conducted u n t i l the 1970 s, when ε-caprolactone monomer became an a r t i c l e of commerce. Since that time, many interesting features such as the biodegradability of 8 have been demonstrated, along with the fact that i t shows interesting compatibility behavior i n blends with a variety of other polymers. In addition, the ring opening polymeri­ zation of 7 can be i n i t i a t e d with diols or t r i o l s and hence im­ portant intermediates for polyurethanes are also made from this material. The polymerization of ε-caprolactam i s one of the older and yet extremely important examples of ring opening polymerizations. The polyamide, commonly referred to as nylon-6, has many important applications; perhaps the most important would be i t s application as a t e x t i l e f i b e r . It especially finds u t i l i t y i n t e x t i l e carpeting materials. From a structure property point of view, i t i s interesting to note that the polyamide 10 has a c r y s t a l l i n e melting point of ~220°C r e l a t i v e to the low value of 50°C for i t s polyester analog 8. This again was one of the major reasons for emphasizing polyamides i n early pioneering polymerization studies. As a last example, we i l l u s t r a t e the ring opening polymeri­ zation of octamethyltetrasiloxane (D4) to y i e l d polydimethylsiloxane. The linear polymer 12 i s the basis of both s i l i c o n e o i l s at low molecular weights and s i l i c o n e rubber at very high molecular weights (M ξ 500,000). Of course, i n order to provide for vulcanization and enhance low temperature behavior, other units such as methyl-vinyl and possibly diphenyl are also incorporated along the chain, as w i l l be discussed later i n this brief review and i n f

w

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

1.

McGRATH

Ring-Opening Polymerization

3

SCHEME I Some Commercially Important Ring Opening Polymerizations 0 / CHo

\ CHo

I ο

I ο /

\ CH

-£cH -0}2

2

0 η

/ \ CH -CH 2

-(•CH -CH2-CH2-CH2-0^2

^0-^CH >C> 2

"(CH ) 2

n

5

7

0 II

I

ΗΝ V

4N-(-CH ^c)2

n

(CH )5 2

10

CH3

CH3

-(•si—o}-

I

*

CH3

CH3

11

12

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING

4

POLYMERIZATION

some of the research papers published in this symposium. The classes of structures that may be appropriate for ring opening polymerizations can be at least s i m p l i s t i c a l l y generalized as i l l u s t r a t e d in Scheme I I . One could, for example, have a c y c l i c SCHEME II Classes of Ring Opening Polymerizations

r η

x

:

^CH >£

-^(CH ) -x )-

2

2

13

y

14 0 Π

0 Η Β

Χ = 0

> y - 2 alkylene oxide, s u l f i d e , amine, lactone, lactam, or cycloalkene. Other groups could of course could be cited but this l i s t should s u f f i c e for the present purposes. The opening of the c y c l i c 13 to y i e l d the linear chain 14 can i n principle proceed with a l l of the mentioned groups. However, i t is usually necessary that the nature of X be such that the heteroatom(s) provides a s i t e for coordination with an appropriate anionic, cationic, or coordination type i n i t i a t o r . Thus one could imagine that i f , for example, X was a r e l a t i v e l y inert methylene group, that a ring potentially able to polymerize might not have an available mechanism to do so since no available " s i t e " for attack could be defined. Thermodynamic Considerations The general transformation of a c y c l i c ring compound to a linear macromolecular chain-like molecule was i l l u s t r a t e d already in Scheme I I . One often here may deal with a possible equilibrium, wherein certain concentrations of the c y c l i c monomer remain after the polymerization reaction has reached equilibrium. Thus, polymerizations of this type are analogous i n several ways to the usual chemical reactions that can only proceed to high y i e l d i f the equilibrium between reactants and product(s) favor the product(s). Moreover, a suitable mechanism must be available which w i l l permit the reaction to proceed. In the case of a ring opening polymeri­ zation a large number of monomer units must be involved in a propagation step to generate a macromolecule. This reminds us that the Gibbs equation shown i n Scheme III must yield a negative free energy change for the propagation reaction i f high molecular weight Scheme III AG = ΔΗ - Τ AS

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

1.

McGRATH

Ring-Opening Polymerization

5

i s to be achieved. It i s appropriate to define also the c r i t e r i a of a c e i l i n g temperature, Tc, which requires one to consider the standard free energy change associated with any ring opening polymerization. This change i s made up of enthalpy and entropy contributions which together with reaction temperatures define the magnitude and sign of the free energy. The chemical structure of the c y c l i c ring thus affects the free energy of the polymerization i n a number of ways. These include the size and ring s t r a i n associated with the monomer, the presence of substituents on the c y c l i c r i n g , the geometrical or stereochemical chain isomerism and s o l i d state morphology (e.g. c r y s t a l l i n i t y ) that might be observed i n the resulting macromolecule· As an i l l u s t r a t i o n , i n Schemes IV and V, data from the l i t e r a t u r e on the enthalpy of polymerization SCHEME IV Representativ

Monomer

Ring Size

Ethylene oxide (OXIRANE) Trimethylene oxide (OXETANE) Tetrahydrofuran (OXOLANE) DIOXANE 1,3 DIOXOCANE

-ΔΗ (kJ/Mole)

3

94.5

4

81

5

15

6 8

~0 53.5

SCHEME V Representative Enthalpy and Entropy Values for Lactam Polymerization ( l c , 38) -ΔΗ (kJ/mole)

AS J/°Kmole

Monomer

Ring Size

Butanolactam Pentanolactam Hexanolactam (Caprolactam) Heptanolactam Octanolactam Nonanolactarn Decanolactam Undecanolactam Dodecanolactam

5 6 7

4.6 7.1 13.8

-30.5 -25.1 4.6

8 9 10 11 12 13

22.6 35.1 23.4 11.7 -2.1 2.9

16.7

for some representative c y c l i c ethers and c y c l i c lactams are provided. One sees for ethylene oxide that the three-membered ring i s quite highly strained and, accordingly, has a t y p i c a l exo­ thermic enthalpy which would also be c h a r a c t e r i s t i c of many v i n y l monomers, such as ethylene or propylene. By contrast, with the

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

6

larger c y c l i c ethers such as THF there i s a clear reduction in the exothermic nature of the process. Moreover, one reaches essentially zero enthalpy for the case of m-dioxane. In the case of the larger rings, the enthalpy again appears to increase; no doubt related to the different conformations that the larger rings can assume. In a similar way one observes analogous data for the lactams, including the most important case of ε-caprolactam (hexanolactam). A summary of the most essential appropriate equations i s provided in Scheme VI. SCHEME VI C e i l i n g Temperature

and Propagation Depropagation Behavior kp

TU*



+

M

*

^

T

N + 1

Equilibrium Constant i s , Κ = *d 1



If Pfl Ξ Pfl+i, Κ =

, where M i s the equilibrium monomer concentration e

[M]

e



AG = -RTlnK = RTln[M]



AG = ΔΗ - TAS = 0 (at the Ceiling



T

e

Temperature)

AH c

= AS + Rln[M]

e

Kinetic and Mechanistic Overview The thermodynamic considerations discussed above are, of course, central to the question of whether or not a particular ring opening polymerization might proceed. However, in order to address the question of how fast such an event might proceed and by what route, one needs to discuss some aspects of the kinetics and mechanisms that are possible for these ring opening polymerizations. The reactions here are almost always ionic and thus proceed in general v i a anionic, cationic or coordination c a t a l y s i s . H i s t o r i ­ c a l l y , free radical processes have not been important. However, Professor Bailey has pioneered the novel free radical routes to ring opening polymerization as evidenced in (28). His manuscript in this book further discusses the p o s s i b i l i t i e s available with his interesting systems. It is also sometimes considered that ring opening reactions may proceed v i a either step-growth, chain-growth or l i v i n g type polymerizations. Indeed, in some cases the d i f f e r e n t i a t i o n i s primarily made on the basis of how molecular weight varies with conversion (4). In this b r i e f review we w i l l attempt merely to i l l u s t r a t e some of the breadth that is possible in ring opening

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

1.

MCGRATH

7

Ring-Opening Polymerization

polymerizations as well as some of the accomplishments, and challenges for the future. One of the oldest and yet most important ring opening polymerizations as eluded to e a r l i e r i s the hydrolytic polymerization of ε-caprolactam (HEXANOLACTAM). The overall processes are outlined i n Scheme VII. For detailed discussions the SCHEME VII Hydrolytic Polymerization of ε-Caprolactam 0 0 II H HO-£-C- ( CH ) 5-N-4-H η

1

ΗΝ X

I + (CH ) 2

9

STEP 1;

H0 2

250°C ^ ^

2

5

1

9 + 13 • H N(CH ) C00H 2

2

5

15

and

θ H N-(CH )5C00 3

2

16 STEP 2:

15 or 16 + 9

0 O H HO(C-(CH )5-N)-H χ 17 2

+

0 II Η HO-(C-(CH )5-N)-H y 18 2

\ HEAT 0 η Η H0-(C-(CH ) -N)-H + H 0 x+y 1? reader i s referred to the reviews of Reimschuessel (35) Hedrick et al (43) and Sekiguchi ( l c ) . The hydrolytic polymerization i s known to involve several stages and a number of e q u i l i b r i a . I n i t i a l l y the lactam i s reacted with a small quantity of water which is capable of opening at least a portion of the monomer to the open chain analog 15 or possible i t s zwitterion 16. The aminocaproic acid i s capable of further attacking the lactam to produce a series of short chain oligomers such as 17 and 18. Eventually i n the second stage of the 2

5

2

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

8

RING-OPENING POLYMERIZATION

process the oligomers are believed to react with each other v i a b a s i c a l l y a step-growth or polycondensation process to produce the high molecular weight polyamide 19. The removal of the water, i n this case, plays one of the c r i t i c a l roles in determining the molecular weight of 1?. Under the conditions u t i l i z e d (approxi­ mately 250°C) there i s a s i g n i f i c a n t monomer polymer equilibrium which may be as high as 8-10 percent of the monomer, plus some very short chain oligomers. Much of the c y c l i c impurities can be removed by water, affording (after drying) a fiber grade nylon-6 by this process. Alternate methods of polymerization of caprolactam are known and discussed i n some depth i n the e a r l i e r cited reviews. The p r i n c i p a l second method that has had much attention i n recent years is outlined i n Scheme VIII. Here we refer to the i n i t i a t e d anionic polymerization of ε-caprolactam. Indeed, for many years i t has been known that at high temperatures strong bases such as 20 are capable of polymerizing J to a high molecular weight polymer very rapidly. At more moderate temperature incapable of polymerizin is no doubt related to the possible resonance forms that amides such as 9 could display, for example, the carbonyl group could be considered to be r e l a t i v e l y negative due to the resonance of the -NH electrons. Thus amides, such as 9, are not readily attacked by the lactam anion such as 21. However, i t was discovered many years ago ( l c ) , that acylated lactams such as structure 22 are capable of inducing polymerization i n the anionic system shown at much lower temperatures. For example, as indicated, i t i s possible to u t i l i z e some fraction of a mole percent of 21 and 23 in the presence of monomer 9 at temperatures at least as low as 140°C. The reaction i s quite rapid due to the fact that the lactam anion 21 can readily attack the acylated lactam 23 to produce the open chain structure 24. Structure 24 i s considered to be able to undergo exchange reactions with the larger amount of monomer present to produce the i n i t i a t e d species structure 25. In this process proton exchange takes place which regenerates the catalyst 21. Thus the the whole process can proceed very rapidly (minutes). The significance as outlined i n Scheme VIII, i s that the polymerization can be conducted below the melting point of the c r y s t a l l i n e nylon-6 (approximately 220°C). As a result of the polymerization temperature and possibly also due to the fact that the polymer c r y s t a l l i z e s , the anionically synthesized nylon-6 can have as l i t t l e as one or two percent residual monomer, as compared to the eight to ten percent t y p i c a l l y observed i n the hydrolytic polymerization. Such a property i s important since i t allows, i n some cases, the u t i l i z a t i o n of the cast nylon d i r e c t l y i n the form of solid gears, fenders, etc. In recent years this process has been often termed reaction injection molding of nylon-6 or RIM (43). Moving on to the area of epoxide polymerization, we would l i k e to point out some of the basic chemistry known for the anionic polymerization of propylene and ethylene oxide. Scheme IX i l l u s t r a t e s some basic ideas which have been established for many years due to the pioneering work of Price and others (20). Potassium hydroxide can attack propylene oxide at the primary carbon thus generating the alkoxide 28. For simplicity purposes we show the intermediate here as an alkoxide (anion and potassium cation).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

Ring-Opening Polymerization

1. McGRATH

9

SCHEME VIII I n i t i a t e d Anionic Polymerization of ε-Caprolactam 0

0

η

η

^c ΗΝ I + MCH )

(Α)

2

NaH

+

Θ9 Na Ν

5

c | (CH ) 2

20 ~

9

+ H

2

5

21

0

I N

(CH ) 2

5

22 0

η

0 Η

η

R = CH3-C-, R'-N-C-, or i n general, an electron withdrawing acyl lactam.

(Β)

In a t y p i c a l polymerization: 0 0 « « CH3-C-N-C

140°C +21

+

9



\l (CH ) 2

5

23 0

0

0

0

κΘ

η

η

η

CH -C-N-(CHo)5-C-N-C + \l 24 (CH ) 3

2

0 0 H H Ν CH3-C-(N-(CH )5-C)-N-C + χ \I 25 (CH )

5

HN-C > \ l (CH ) 2

5

0

η

2

2

21

Propagation

5

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING

10

POLYMERIZATION

SCHEME IX Anionic Polymerization of Propylene Oxide

Λ KOH

+

CH -CH-CH 2

3

26

27

Initiation

CH

3

28

Propagation

27, then H+

H0-

p

A

s

C

H

2

C

H

2

0

L

i

( 2 )

Β

t i o n of t h i s derivative (B) a f t e r hydrolysis had e s s e n t i a l l y the same retention volume as an aliquot of the o r i g i n a l p o l y ( s t y r y l ) l i t h i u m (A) which had been quenched with _t-butanol (see Figure 1). The molecular weight d i s t r i b u t i o n of A as calculated from the GPC data was 1.04 (Mtf/tyO. An aliquot of the polymeric l i t h i u m alkoxide (B) (8 mmoles) was dissolved i n ca. 300 mL of a 2/1 (v/v) mixture of ben­ zene and dimethylsulfoxide using high vacuum techniques(17) a f t e r removal of the o r i g i n a l benzene and excess ethylene oxide from the i n i t i a l alkoxyethylation reaction (Equation 2). Ethylene oxide (0.52 moles) was then condense placed i n a 40°C bath fo reaction was terminated by addition of a few mL of degassed acetic acid. The polymer product isolated a f t e r p r e c i p i t a t i o n and drying cor­ responded to an o v e r a l l y i e l d of 83%, which indicates a 70% conver­ sion of ethylene oxide. The size exclusion chromatographic retention volume_of__this product (see Figure 2) corresponds to an Μ η ^ ^ 3 4 0 0 with (M /M )Qpc=1.04. Several s a l i e n t features of these r e s u l t s deserve s p e c i f i c comment. Both the narrow molecular weight d i s t r i ­ bution of the product, PS-PEO, diblock polymer and the absence of any observable peak corresponding to the o r i g i n a l polystyrene block (observable by GPC i n synthetic mixtures of hydrolyzed A and PS-PEO), indicate that (a) the hydroxyethylation reaction (Equation 2) occurs e s s e n t i a l l y quantitatively i n benzene solution; and (b) no evidence for chain termination or chain transfer i s apparent i n the polymeri­ zation of ethylene oxide with l i t h i u m as counterion i n a mixture of benzene/dimethylsulfoxide. The 60 MHZ H-NMR spectrum of the PS-PEO diblock (Figure 3) c l e a r l y indicates the presence of the p o l y ( e t h y l ­ ene oxide) segment. The calculated r a t i o of the integrated i n t e n s i ­ t i e s for the aromatic to -CH 0- protons corresponds to 1.1, while the i n t e n s i t y r a t i o calculated from the GPC molecular weights corresponds to 1.0. Thus, a dipolar aprotic solvent such as dimethylsulfoxide pro­ vides the necessary solvation and p o l a r i t y to render l i t h i u m alkoxides as e f f e c t i v e i n i t i a t o r s for ethylene oxide polymerization. Work i s underway to further explore the scope and k i n e t i c s of t h i s important polymerization system. Several polymerizations of ethylene oxide with sodium t r i b u t y l magnesate have been performed. Reactions at 60°C for 3 days produced polymer i n 22% y i e l d . It was necessary to heat the reactions mix­ tures for 12 days at 60°C to achieve a conversion of 56%. Molecular weights were l e s s than stoichiometric and the molecular weight d i s ­ t r i b u t i o n s as determined by GPC were somewhat broad but symmetrical. β

w

n

X

2

Solution Properties of Styrene-Ethylene Oxide Block Polymers. During the course of our studies of synthetic routes to poly(styrene-bethylene oxide), we have undertaken an investigation of the solution

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

QUIRK AND SEUNG

Figure 1.

Anionic Polymerization of Ethylene Oxide

Size exclusion chromatogram of polystyrene.

ELUTION VOLUME(ML) Figure 2.

Size exclusion chromatogram of poly(styrene-b-ethy 1 oxide).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING

42

POLYMERIZATION

properties of these polymers. We have compared a diblock polymer, po l y ( s tyrene-b-ethylene oxide) (PS-PEO), with the corresponding t r i b l o c k polymer, poly(styrene-b-ethylene oxide-b-styrene)(PS-PEO-PS). The t r i b l o c k polymer has the same styrene end segment lengths as the diblock polymer, and the poly(ethylene oxide) center block i n the t r i b l o c k i s twice the poly(ethylene oxide) segment length i n the diblock as shown i n Table I I . Both PS-PEO and PS-PEO-PS exhibited the same retention volume i n tetrahydrofuran using a three-column set Table I I .

Molecular Weight Characterization of PS-PEO and PS-PEO-PS

Polymer PS-PEO (Diblock)

Stoichiometric Molecular Weight (g/mol) a

83,000

M

n (g/mol)

b

82,800

PS-PEO-PS (Triblock) (35-96-35) The numbers i n parentheses correspond to the stoichiometric molecular weights f o r the individual block segments ( x l 0 ~ ) based on the r a t i o of gm of monomer charged to the moles of initiator. 3

Determined by membrane osmometry. of μ-styragel columns. This surprising r e s u l t was compounded by the fact that the measured i n t r i n s i c v i s c o s i t i e s i n tetrahydrofuran were 75 ml/g and 71 ml/g for the diblock and the t r i b l o c k , respectively. Thus, the t r i b l o c k polymer apparently exhibits the same hydrodynamic volume and v i s c o s i t y as the diblock polymer which has one-half of the molecular weight of the t r i b l o c k . These unusual observations probably r e f l e c t the fact that tetrahydrofuran i s l i s t e d as non-solvent for poly(ethylene oxide)(21) and p r e c i p i t a t e s from a 1% solution at 18°C (22). This phenomenon was explored further by examining the behavior of these block polymers i n chloroform, a good solvent for polystyrene and poly(ethylene oxide)(21). The size exclusion chromatograms of these polymers i n chloroform are shown i n Figure 4. The retention volumes were 13.5 ml and 14.0 ml for the t r i b l o c k and diblock, respectively. For the polystyrene standards, a retention volume d i f ­ ference of 1.2 ml (versus 0.5 ml observed for the block polymers) would be expected for a doubling of the molecular weight from 83,000 to 166,000. Further evidence for the unusually small increase i n hydrodynamic volume for the t r i b l o c k polymer r e l a t i v e to the diblock i n chloroform has been obtained from their i n t r i n s i c v i s c o s i t i e s and second v i r i a l c o e f f i c i e n t s as shown i n Table I I I . It i t noteworthy that the diblock and t r i b l o c k polymers i n toluene solution could not be separated by u l t r a c e n t r i f u g a t i o n . A 50/50 mixture of the two polymers i n toluene exhibited a single peak throughout the sedimentation process with the ultracentrifuge oper­ ating at a speed of 28,000 rpm. In conclusion, a l l of the evidence from solution properties of a PS-PEO-PS block polymer indicates that

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

3.

QUIRK A N D SEUNG

8.0

7.0

Figure 3.

Anionic Polymerization of Ethylene Oxide

6.0

5.0 """' 4.0

3.0

2.0

1.0

43

0

60 MHz *H-NMR spectrum of poly(styrene-b-ethylene oxide),

...Triblock Diblock

10

15

20

v («i) E

ELUTION VOLUME(ML)

Figure 4.

Size exclusion chromatograms of poly(styrene-b-ethylene

oxide-b-styrene) and poly ( s tyrene-b-ethylene

oxide).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

44

Table I I I .

Polymer

[η] (ml/g)

PS-PEO PS-PEO-PS

124 132

Solution Characterization of PS-PEO and PS-PEO-PS i n Chloroform. Huggins Constant, k i 0.40 0.34

Kraemer Constant, k -0.13 -0.14

AaxlO** (ml/mol g ) 2

2

6.63 5.01

this polymer exhibits unique hydrodynamic properties when compared to the corresponding diblock polymer with one-half of the molecular weight of the t r i b l o c k . Further work i s i n progress to characterize the solution properties of these polymers. Acknowledgments The authors would l i k e t Mr. Dennis McFay who carried out the i n i t i a l synthetic and solution property experiments at Michigan Molecular I n s t i t u t e .

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Sawada, H. J. Macromol. Sci.-Rev. Macromol. Chem., 1970, (C5(1), 151. Morton, M. "Anionic Polymerization: Principles and Practice"; Academic Press: New York, 1983; p. 52. Boileau, S. in "Anionic Polymerization: Kinetics, Mechanisms, and Synthesis"; McGrath, J.E., Ed.; ACS Symposium Series No. 166, American Chemical Society: Washington, D.C., 1981; p. 283. Bailey, F.E.; Koleske, J.V. "Poly(ethylene Oxide)"; Academic Press: New York, 1976. St. Pierre, L.E.; Price, C.C. J. Am. Chem. Soc., 1956, 78, 3432. Lebedev, N.N.; Baranov, Yu.I. Polym. Sci. USSR, 1966, 8, 211. Doroshenko, N.P.; Spirin, Yu.L. Polym. Sci. USSR, 1970, 12, 2812. Cabasso, F.; Zilkha, A. J. Macromol. Sci.-Chem., 1974, A8(8), 1313. Guilbert, Y.; Brossas, J. Polym. Bull., 1979, 1, 293. Chang, C.J.; Kiesel, R.F.; Hogen-Esch, T.E. J. Am. Chem. Soc., 1973, 95, 8446. Solov'yanov, A.A.; Kazanskii, K.S. Polym. Sci. USSR, 1970, 12, 2812. Wakefield, B.J. "The Chemistry of Organolithium Compounds"; Pergamon Press: Elmsford, N.Y., 1974; p. 199. Young, R.N.; Quirk, R.P.; Fetters, L.J. Adv. Polym. Sci., 1984, 56, 1. Dudek, T.J. Ph.D. Thesis, University of Akron, 1961, p. 74. Kobayashi, S.; Kaku, M.; Mizutani, T.; Saegusa, T. Polym. Bull., 1983, 9, 169. Ziegler, K.; Dislich, H. Chem. Ber., 1957, 90, 1107. Morton, M.M.; Fetters, L.J. Rubber Chem. Tech., 48, 359 (1975). Halaska, V.; Lochmann, L.; Lim, D.; Coll. Czech. Chem. Commun., 1968, 33, 3245. Figueruelo, J.E.; Worsfold, D.J. Eur. Polym. J., 1968. 4, 439.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

3.

QUIRK A N D SEUNG

Anionic Polymerization of Ethylene Oxide

20.

45

Anderson, B.C.; Andrews, G.D.; Arthur, P., Jr.; Jacobson, H.W.; Melby, L.R.; Playtis, A.J.; Sharkey, W.H. Macromolecules, 1981, 14, 1599. 21. Fuchs, O.; Suhr, H.-H. in "Polymer Handbook," Second ed.; Brandrup, J.; Immergut, E.H., Eds.; Wiley-Interscience: New York, 1975; p. IV-241-265. 22. Stone, F.W.; Stratta, J.J. in "Encyclopedia of Polymer Science and Technology"; N. Bikales, Ed.; John Wiley and Sons, Inc.: New York, 1967; Vol. 6; p. 114. RECEIVED September 14, 1984

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

4 Free Radical Ring-Opening Polymerization W I L L I A M J. BAILEY Department of Chemistry, University of Maryland, College Park, M D 20742

Free radical ring-opening polymerization has pre­ viously been quite rare with the only examples being cyclopropane derivatives and o-xylylene dimer. This fact is surprising in view of the fact that ionic ring­ -opening polymerization is very common. Since a carbon­ -oxygen double bon carbon-carbon doubl ducing an oxygen atom into an unsaturated cyclic monomer would permit free radical ring-opening poly­ merization. Thus it was shown that cyclic ketene acetals, cyclic ketene aminals, cyclic vinyl ethers, unsaturated spiro ortho carbonates, and unsaturated spiro ortho esters, would a l l undergo such polymeriza­ tion. Furthermore, a l l of these monomers would copoly­ merize with a wide variety of vinyl monomers with the introduction of functional groups, such as esters, thioesters, amides, ketones, and carbonates, into the backbone of the addition polymers. This copolymerization makes possible the synthesis of biodegradable polymers, functionally terminated oligomers, polymers with enhanced thermal stability, and monomer mixtures which expand upon polymerization. In a research program to find monomers which expand upon polymeriza­ tion i t was desirable to have available monomers which would undergo double ring-opening polymerization by a free radical mechanism. However, a search of the literature revealed that there were very few examples of any free radical ring-opening polymerization. For example Takahashi (1) reported that during the free radical poly­ merization of vinylcyclopropane the cyclopropane ring opened to give a polymer containing about 80% 1,5-units and about 20% of undeter­ mined structural units but no cyclopropane rings. Apparently the radical adds to the vinyl group to give the intermediate cyclopropylmethyl radical which opens at a rate faster than the addition to the double bond of another monomer. The driving force for the poly­ merization is the relief of the strain of the three-membered ring. Somewhat similar results were obtained with the chloro derivatives. Very recently, Cho and Ann (2) studied the related ma Ionic ester derivative, which underwent Tree radical ring-opening polymerization to produce a high molecular weight polymer containing only the 1,5-units. 0097

AmeBtcaffe6ute9f9^/o

© 1985 ^ e T J ç a D . C h d t e ^ ^ o c i e t y

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

48

AIBN CH9-CH-CH-Œ9

\/ CH

Oi -CH=CH-CH -CH 2

2

z

χ 2

(80% 1,5-units; 20% unknown units)

repeat ]

R-CHo-CH-CH-CHo \ / CH

-> R-CH -CH=CH

^CH

2

e 2

2

Hall and coworker bicyclo[1.1.0]butane would polymerize by free radicals by cleavage of the highly strained central bond. R

e

.00 CH 2

3

00 CH 2

3

Errede (4) showed that the dimer of o-xylylene would undergo free radical ring-opening polymerization to give the corresponding poly-o-xylylene· CH9

Π4-CH 2

2

,CH — 2

repeat R

I

CH

2

In this case the driving force for the ring-opening step is the for­ mation of the aromatic ring. Finally the ring-opening polymeriza­ tion of S3 has been postulated to involve free radicals ( 5 ) .

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

4.

BAILEY

Free Radical Ring-Opening Polymerization

49

The dearth of examples of free radical ring-opening polymeri­ zation is rather surprising in view of the fact that the ionic ringopening polymerization of heterocyclic compounds, such as ethylene oxide, tetrahydrofuran, ethylenimine, 3-propiolactone, and caprolactam, as well as the Ziegler-Natta ring opening of cyclic olefins, such as cyclopentene and norbornene, are quite common. One explana­ tion is that unstrained five- and six-membered carbocyclic rings usually are involved in ring-closing reactions rather than ring opening. For example, Butler and Angelo (6) in 1957 found that, when diallyldimethylammonium bromide was polymerized by a free radi­ cal mechanism, a soluble polymer containing five-membered rings was obtained by an inter-intramolecular polymerization. R* + CH2

CH

ι

R-CH

II

CH

I I

CH

CH*

CH

XHo

CH

2

I

2

2

^y

/ \

/\ (H

3

2

I CH

2

^y

CH

R-CH-CH

CH

u CH I I

CH

3

3

e

CH-CHo

CH

3

R+

I 2

^CH

/\ CH CH 3

repeat

2

3

Apparently the reaction is kinetically controlled to form the five-membered ring rather than the t^rraodynamically favored sixmembered ring. The recent data of Maillard, Forest and Ingold (7) can be used to explain the course of some of these ring-opening and ring-closing polymerizations. When they studied the transformations in the cyclopropylmethyl and the cyclopentylmethyl series by electron spin resonance, they found that in the case of the threemembered radical the reaction involves ring-opening since the energy is favorable by about 6 kcal and the rate of the reaction is very high. In the case of the five-membered ring system they found that the reaction proceeds in the direction of ring-closure since the energetics of that reaction is favorable by about 8 kcal and the rate of the ring closure is also moderately high. Free Radical Ring-Opening of Cyclic Ketene Acetals Since the carbon-oxygen double bond is at least 50-60 kcal/mole more stable than the carbon-carbon double bond (8), we estimated that the introduction of an oxygen atom in place of "the carbon atom in the cyclopentylmethyl radical would favor the reverse reaction or the

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

50

ring opening. In other words the ring-opening reaction would be favored by at least 40 kcal/mole by producing the more stable carbonyl double bond. A search of the literature revealed several ring systems containing an oxygen atom that would undergo a ring-opening reaction in the presence of free radical catalysts. One such case was the cyclic formal, 1,3-dioxolane, which Maillard, Cazaux, and La lande (9) found rearranged to ethyl formate when heated at 160° C. CH?

'CH

/ \ 0

R*

0

1 2

0

1

I

0

I

>

CH -CH 2

ο I

2

0

I CH -CH

2

2

CH /w

CH -CH 2

/ \\

0

I

160°C

2

0

0

— »

I

CH -CH

CH

/ \

e

2

CH

/\

ο

0

0

1

I

Œ2-Œ3

CH2-CH The reaction could be rationalized as indicated where the driving force for the ring-opening step in the chain reaction was the formation of the stable carbon-oxygen double bond in the final ester. With the knowledge that such a ring system would undergo cleavage, i t seemed to be a fairly straight forward process to synthesize a monomer that would undergo ring-opening polymerization by introducing a double bond at the carbon atom flanked by the two oxygens· The monomer desired for this ring-opening polymerization had indeed been prepared by McElvain and Gurry (10) in 1948. Although 0-CH

2

0-CH

2

2

di-tert-butyl peroxide

0 H - - C H - C-0-CH 0 -CH -

5

CH < 2

2

2

2

160°C

I

II repeat R

e

•/ΜΉ R-CH -Cv I 0-CH

0 u

2

R-CH -C

2

III

2

2

•f

2

V

0-CH

2

IV

Johnson, Barnes, and McElvain (11) had treated diethyl ketene aceta1 with peroxide and had reported Tnat there was no reaction, no such

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

4. BAILEY

Free Radical Ring-Opening Polymerization

51

study was reported for the 2-methylene-l,3-dioxolane (I). A rein­ vestigation of the cyclic ketene acetal I was therefore undertaken. This polyester II is difficult to synthesize with high molecular weight from the γ-hydroxybutyric acid because of the stability of the competing lactone. When the polymerization is carried out at lower temperatures, the ring opening is not complete. Thus at 60° C only 50% of the rings are opened to give a random copolymer of the following struc­ ture (12):

Qi

2

0

ι 1

0

I 1

Even at 120° C only 87% of the rings are opened. The uno pened radical III apparently can add directly to the monomer I in competition with the ring-opening process to form the open chain /0-Œ CH «C I 0-CH

2

v

2

0-CH R-CH-C-CH-CC I / \ 0-CH 0 0

2

2

2

2

2

1

0-CH R-CH -C^ 0-CH

2

I

CH -CH

2

2

2

2

III

0 » CH R-CH -C I 0-CH #

2

x

lSO

2

S

2

IV radical IV. High dilution was found to favor the ring-opening pro­ cess since the addition of III to the monomer I is a second order reaction while the conversion of III to the open chain radical is f i r s t order. The extent of ring opening is kinetically controlled with a direct competition between the rate of direct addition, k;Q, and the rate of ring opening, k i . In a program to find other cyclic ketene acetals that would undergo quantitative ring-opening even at room temperature we pre­ pared the seven-membered ketene acetal, 2-methylene-l,3-dioxepane (V), which underwent essentially complete ring-opening at roan tem­ perature (13-15). This process makes possible the quantitative introduction "OF an ester group in the backbone of an addition polymer. s 0

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

52

0 di-tert-butyl » -|Œ2-G-0-(CH2)4f-. peroxide 120°C VI

ι

O-CHo-CHo CH < I 0-Oi -CH2 2

2

R-

repeat

.,0-CH -CH R-CH -C I O-Œ2-CH9 VII 2

2

e

» CH -CH R-CH -C I

2

2

N

1

2

2

K

1

Apparently the seven-membered ring increases the steric hindrance in the intermediate free radical VII to eliminate practically a l l of the direct addition and also introduces a small amount of strain so that the ring-opening to the radical VIII i s accelerated. Additional cyclic ketene ace ta Is (16-18) that have been studied have included the 4-phenyl-2-methyIene-l,3-dioxepane (IX) which undergoes quantitative ring-opening to give the polyester X. Apparently the ring-opening step from XI to XII is greatly enhanced

O-Qi-φ CH =C I 0-CH 2

»

N

-+CH -C-OCH -CH2

2

2

IX

R-

repeat

. .O-CH-φ R-CH -C\ I 0-CH 2

2

XI

-> R-CH -C 2

I OCH

N

2

XII

by the formation of the relatively stable benzyl radical in XII even though XL is a five-membered ring analogous to the radical III. Nitrogen and Sulfur Analogs of Cyclic Ketene Acetals Since an amide group is more stable than an ester group, the nitro­ gen analog XIII of the cyclic ketene acetal was synthesized and polymerized to give the polyamide XIV.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

4. BAILEY

Free Radical Ring-Opening Polymerization

0 M 0 Ν (φΟ0-) * -N-Œ -Œ -+Œ -C-N-(H -Œ 4-CH -C-N-80° C Œ CH CH

0-CH CH =C; I N-CH

2

2

2

2

2

I

53

2

2

2

2

3

3

3

2

(100% ring opened)

CH

3

XIV

XIII

repeat

0 O-CH R-CH -C^ I N-CH v

2

I

2

N-CHo

2

CH

I

3

CH

3

XV XVI In contrast with the 2-methylene-1,3-dioxolane (I) the nitrogen ana­ log XIII undergoes essentially quantitative ring opening even at roan temperature. Although the sulfur analog of the cyclic ketene acetal I was prepared and polymerized, apparently the resulting thioester i s higher energy than the ordinary ester and therefore retards the extent of ring opening. Even at 120°C only 45% of the rings were opened (19-20). 0-CH CH - 0 (7)

Cation to Anion Attempts to effect this transformation e f f i c i e n t l y have not been very successful. Mono-or difunctional l i v i n g poly THF was prepared using the appropriate cationic i n i t i a t o r and subsequently reacted with the sodium salt of cinnamyl alcohol or of l-phenyl-l-buten-4-ol to y i e l d s t y r y l groups on terminal ligands (Equation 8) i n which η • 1 or 2 respectively (11). In both cases reaction was shown to

~0(CH )4 ~ θ"*"] 2

PF

+ 0 (CH )

6

2

n

CH = CH (8)

1 ~0(CH ) 2

4

- 0 - (CH ) 2

n

Ô - CH - CH + PF

6

be quantitative, and the materials were subsequently isolated, redissolved i n THF or benzene and reacted with η-butyl lithium to generate s t y r y l anions (Equation 9) which should then have co-

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

6.

RICHARDS

Synthesis of Novel Block Copolymers

0(CH )4 - 0 - ( C H ) 2

2

n

- CH = CH + η BuLi

L 0(CH ) 2

4

91

(9)

riBu^C^

- 0 - (CH ) 2

n

- CH - CH Li+

polymerized freshly added styrene monomer. Although the red color c h a r a c t e r i s t i c of s t y r y l anions was generated rapidly on introduction of n-butyllithium and the styrene subsequently added was polymerized, molecular weight determinations on the isolated polymer indicated that onl participated i n the copolymerizatio low e f f i c i e n c y of block copolymer formation i s not known at present. A second approach to effecting this transformation was attempted by reaction of l i v i n g poly THF with a primary amine to generate a terminal secondary amine ligand (12) (Equation 10), and

O(CH ) 2

4

- 0 +

PF

6

+ RNH

2



0(CH ) 2

4

- NRH + HPF

(10)

6

by i t s subsequent reaction with potassium to generate the amide anion. The amination reaction can be made quantitative (13), as can the metallation. These macromolecular i n i t i a t o r s polymerized added styrene quantitatively, but the rate of i n i t i a t i o n versus that of polymerization was slow. Consequently only about 30% of the poly THF chains produced block copolymers, and the molecular weight d i s t r i b u t i o n s were broad ( t y p i c a l l y - 2 to 3). In summary, the cation to anion transformation has not as yet been made an e f f i c i e n t process, and further development i s required i n this area. Cation to Free Radical This transformation has been e f f e c t i v e l y achieved by combining techniques devised within our Group with those developed at the Liverpool, and the hitherto unpublished results described here were obtained cooperatively at the l a t t e r i n s t i t u t i o n (14). Living poly THF was terminated by the lithium salt of bromoacetic acid to y i e l d a polymer possessing terminal bromide ligands (Equation 11). This reaction can be made e s s e n t i a l l y ~~0(CH ) - 0 + 2

4

PF

6

+ L i 00CCH Br —• ~~0(CH ) -00CCH Br + L i P F 2

2

4

2

6

(11)

quantitative, and the material isolated and dissolved i n methyl methacrylate (MMA) into which dimanganese decacarbonyl has been added as photoinitiator (λ = 436 nm). Irradiation resulted i n

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

92

free r a d i c a l formation (Equation 12) and the consequent formation of AB poly (THF-b-MMA) copolymer with some ABA material also present.

0(CH )4-00CCH Br+Me(0) — • 2

2

0(CH ) 00CCH # + Me(I)Br 2

4

(12)

2

The r e l a t i v e proportions of the two copolymers are d i r e c t l y dependent on the nature of the PMMA radical terminating process under the experimental conditions, which at 25°C i s 70/30 disproportionation/combination. The photoinitiating system has been studied i n great d e t a i l with small molecule organic halides, and has been shown to be very e f f i c i e n t (15). Similar high e f f i c i e n c i e s have been observed with bromide terminated poly THF, with no evidence of formation of homo PMMA being obtained. Clearly, this technique can be extended to include other monomers polymerizable b begun using chloroprene s p e c i f i c i t y and purity of the product i s largely controlled by the detailed kinetics of the radical polymerization process, i n particular the prominence of chain transfer reactions and the nature of the termination step which w i l l , of course, vary from monomer to monomer. Reactions of Living Anionic Polymers With Living Poly THF A potentially simpler approach to the synthesis of block copolymers containing poly THF i s the direct reaction of l i v i n g cationic homopoly THF with anionic l i v i n g polymers (Equation 13). Assuming 0 ( C H ) - (T+J 2

4

P F + Li+~M 6

0(CH ) -M 2

4

+ L i P F (13) 6

a clean metathetical reaction, this route could lead to AB, ABA, BAB and (AB) block copolymers, depending on the f u n c t i o n a l i t i e s of the two reagents. The f e a s i b i l i t y of this approach was f i r s t demonstrated by Berger et a l . (16) using l i v i n g polystyrene but, although they showed that block copolymer was formed, they did not determine the e f f i c i e n c y of the reaction. We have studied this reaction i n more d e t a i l (17), and have shown that with l i v i n g polystyrene the process i s e s s e n t i a l l y quantitative. A l l combinations of block copolymer structures l i s t e d above were prepared i n very high y i e l d , and calculations based on the molecular weight of (AB) obtained when difunctional reagents were employed gave a reaction e f f i c i e n c y of at least 95%. Similar reactions involving l i v i n g poly (ormethylstyrene) were not so e f f i c i e n t , the coupling e f f i c i e n c y being of the order of 20% only (18). The competing reaction i n this case was i d e n t i f i e d as being one of proton abstraction from l i v i n g poly THF to yield an unsaturated terminal group (Equation 14). The effectiveness of this coupling process i n the synthesis of block copolymers with l i v i n g poly THF i s , therefore, highly n

n

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

6.

RICHARDS

Synthesis of Novel Block Copolymers

CH O(CH ) 2

PF

4

6

O(CH ) 2

2

CH = CH

2

3

+ Li+ " C - CH

CH

93

2

(14)

3

+ HC - CH

2

+ L i PF

6

dependent on the nature of the anionic l i v i n g polymer involved, and so each system requires polymer combination hithert and the l i v i n g polydienes. If metathesis proves e f f i c i e n t , i t s development could generate many block copolymers of great morphological i n t e r e s t . Block Copolymers With Ionic Linking Groups More recently we have begun to explore the synthesis of block copolymers i n which the linking of the polymeric segments i s by a stable ionic group. Two such synthetic routes involve l i v i n g poly THF, and the reaction schemes are outlined below. In the e a r l i e r approach, l i v i n g poly THF was reacted with a secondary amine to generate a polymer possessing t e r t i a r y amine end groups (19) (cf Equation 10). The product was then isolated and subsequently reacted with polystyrene possessing a terminal bromide ligand derived either by direct reaction with bromine (Equation 2) or by reaction with m-xylylyl dibromide (Equation 3). Gpc studies showed no observable quaternisation with the former material, but with the l a t t e r material there was evidence of s i g n i f i c a n t reaction (Equation 15), albeit only after a period of several days at ambient temperatures. Indeed, although the gpc traces were complicated by

the presence of unreactive coupled polystyrene, there was a strong indication of complete consumption of the bromine terminated polystyrene component under the reaction conditions p r e v a i l i n g .

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

94

An alternative approach to synthesizing block copolymers with ionic linking groups was later developed. Polystyrene with t e r t i a r y amine and groups was prepared by the reaction of l i v i n g polystyrene with a, w-chloroamines such as 3-(dimethylamino)propyl chloride (20) (Equation (16). This reaction was shown to take place with at least

+

~~CH -CH L i + C1(CH )3N(CH ) 2

2

3

2

— • ~~CH -CH-(CH ) N(CH ) +LiCl (16) 2

2

3

3

2

95% e f f i c i e n c y , and the product was precipitated, purified and redissolved i n THF. A molar equivalent of l i v i n g poly THF was then added and the resulting material was i s o l a t e d . Gpc examination showed that block copolymer had been formed i n v i r t u a l l y quantitative y i e l d (Equatio found to be very fast a be e a s i l y exchanged i f desired, the product of reaction 17 can be

~CH -CH-(CH ) -N(CH ) + PF 2

2

3

3

2

E> +

6

0-(CH )40 2

+ ~CH -CH-(CH ) -N(CH ) (CH ) 0~~ P F 2

2

3

3

2

2

4

6

(17)

made s t r u c t u r a l l y very similar to that of Equation 15, and the reaction involving l i v i n g poly THF d i r e c t l y , because of i t s rapidity and e f f i c i e n c y , must therefore be regarded as the preferred synthetic route to such block copolymers. The r e l a t i v e rapidity of the quaternisation reaction involving l i v i n g poly THF compared with polystyrene bromide i s d i r e c t l y related to the greater e l e c t r o p h i l i c i t y of the former reagent. This f a c i l e reaction has also been used to prepare homopoly THF with quaternary ammonium salt linkages at predetermined positions along the polymer chain (19). Thus t e r t i a r y amine terminated poly THF has been reacted with further l i v i n g poly THF to generate a quaternised homopolymer (of equation 17). Gpc analysis of the process again indicated that the reaction was both f a c i l e and s p e c i f i c . The molecular weight of the product and the position of the quaternary ammonium grouping along the chain are therefore e a s i l y and independently controlled by appropriate choice of the molecular weights of the component poly THF reagents.

Literature Cited 1. Szwarc, M. 'Carbanions, Living Polymers and Electron Transfer Processes' Interscience, 1968. 2. Penczek, S.; Kubiza, P.; Matyjaszewski, K. 'Cationic Ring­ -Opening Polymerization', Advances in Polymer Science 37, Springer-Verlag 1980.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

6.

RICHARDS

3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

Synthesis of Novel Block Copolymers

95

Richards, D. H.; Szwarc, M. Trans Faraday Soc., (1959), 58, 1644. Croucher, T. G.; Wetton, R. E. Polymer (1967), 17, 205. Burgess, F. J.; Cunliffe, Α. V.; Richards D. H.; Thompson, D. Polymer, (1978), 19, 334. Richards, D. H.; Thompson, D. Polymer, (1979), 20, 1439. Burgess, F. J.; Cunliffe, Α. V.; MacCallum, J. R.; Richards, D. H. Polymer, (1977), 18, 719. Burgess, F. J.; Cunliffe, Α. V.; MacCallum, J. R.; Richards, D. H. Polymer, (1977), 18, 726. Burgess, F. J.; Cunliffe, Α. V.; Dawkins, J. V.; Richards, D. H., Polymer, (1977) 18, 733. Richards, D. H.; Viguier, unpublished results. Abadie, M. J. H.; Schue, F.; Souel, T.; Hartley, D. B.; Richard, D. H. Polymer, (1982), 23, 445. Cohen, P.; Abadie, M. J. M.; Schue, F.; Richards, D. H. Polymer (1982), 23 Cohen, P.; Abadie, Polymer, (1982), 23, 1350. Bamford, C. H.; Eastmond, G. C.; Woo, J.; Richards, D. Η., unpublished results. Bamford, C. H. "Reactivity, Mechanisms and Structure in Polymer Chemistry' Eds Jenkins, A. D. and Ledwith, A. Wiley, NY (1974), 52. Berger, G.; Levy, M.; Vofsi, D. J. Polymer Sci. (B) (1966), 4, 183. Richards, D. H.; Kingston, S. B.; Souel, T. Polymer (1978), 19, 68. Richards, D. H.; Kingston, S. B.; Souel, T. Polymer (1978), 19, 806. Hartley, D. B.; Hayes, M. S.; Richards, D. H. Polymer (1981), 22, 1081. Richards, D. H.; Service, D. M.; Stewart, M. J. Brit Polym J, in press. Hurley, J. N.; Richards, D. H.; Stewart, M. J., unpublished results. Noshay, Α.; McGrath, J. E. "Block Copolymers: Overview and Critical Survey" Academic Press (1977).

RECEIVED March 27,

1985

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

7 Metal-Alcoholate Initiators Sources of Questions and Answers in Ring-Opening Polymerization of Heterocyclic Monomers P. TEYSSIÉ, J. P. BIOUL, P. C O N D É , J . DRUET, J . H E U S C H E N , R. J É R Ô M E , Τ. O U H A D I , and R. WARIN Laboratory of Macromolecular Chemistry and Organic Catalysis, University of Liège, Sart Tilman, 4000 Liège-Belgium

Soluble μ-oxo-bimetallic trinuclea alkoxide rank among th ranes polymerizatio hig polyethers After an i n i t i a l rearrangement, coordination propagation proceeds on three types of centers: non-selective ones, producing oligomers of spe­ cific lenghts, and other ones generating high M.W. chains either atactic, or stereoregular (up to 80 % isotactic). The relative impor­ tance of these three centers, working through similar but competitive pathways, can be deter­ mined to a large extent by modifying the struc­ ture of the aggregates, implying "topochemical control" in solution. These features are tentatively related to a detailed H, C and Al NMR study, demonstrating the rigidity of these aggregates which offer different coor­ dination sites for the monomer. The initiators also polymerize most lactones, the perfectly living character of the process allowing inte­ resting block copolymerizations. Their acti­ vity towards cumulenes, i.e. isocyanates and CO , also leads to valuable reactions. 1

13

27

2

In agreement with a former proposal by E. Vandenbergh (1) and with the mode o f p r e p a r a t i o n o f d i f f e r e n t a c t i v e systems, polynuclear s t r u c t u r e s are c l e a r l y a key feature f o r the design o f c a t a l y s t s able to polymerize s u b s t i t u t e d oxiranes i n t o very high mo­ l e c u l a r weight p o l y e t h e r s . In an e x p l o r a t o r y approach based on these premises and aimed a t the s y n t h e s i s o f w e l l c h a r a c t e r i z e d and v e r s a t i l e specie o f that type, we have shown indeed (2) that s o l u b l e μ-οχο-bimetallic t r i n u c l e a r alkoxides having the general formula £RO) ni-O-MÏ-O-H (0R)^j_ rank among the best known 1

0097-6156/ 85/ 0286-O097S06.00/ 0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING

98

POLYMERIZATION

i n i t i a t o r s f o r oxiranes p o l y m e r i z a t i o n , y i e l d i n g products having molecular weights i n the 10°range and d i s p l a y i n g i n some cases an amazing degree of s t e r e o r e g u l a r i t y d e s p i tes the p e r f e c t s o l u b i l i t y of the i n i t i a t o r and the p o l y mer. These compounds, p a r t i c u l a r l y those where M =A1 and M= Zn, have proven to be very i n t e r e s t i n g models, a l l o w i n g a b e t t e r understanding of s e v e r a l determinant phenomena i n r i n g opening p o l y m e r i z a t i o n , as w e l l as i n other areas of chemistry(3). I t i s the purpose of t h i s paper to sum­ marize the c u r r e n t status of the f i e l d , and to i n d i c a t e i t s p o t e n t i a l developments .(see a l s o r e f . 4b). X

2

Synthesis and p r o p e r t i e s of a c t i v e y - o x o - b i m e t a l l i c alkoxides - Preparation : The poîynucïear"system, mentally recognized to give a c t i v e systems f o r the high M.W. p o l y m e r i z a t i o n of oxiranes, i s a thermal condensa­ t i o n process between metal alkoxides and carboxylates, i.e.

Conveniently c a r r i e d out i n a hydrocarbon solvent l i k e d e c a l i n e , t h i s r e a c t i o n i s c h a r a c t e r i z e d by a r a p i d f i r s t step, followed by a more d i f f i c u l t e l i m i n a t i o n (at 200°C) of the second e s t e r molecule; i t i s important to d r i v e the e q u i l i b r i u m to completion by d i s t i l l a t i o n , and to avoid so c o o r d i n a t i o n of by products to the c a t a l y s t . I t must a l s o be r e a l i z e d t h a t too high temperatures may f u r t h e r promote formation of Al-O-Al bonds upon e l i m i n a ­ t i o n of ether (or a l c o h o l + o l e f i n ) , a d e t r i m e n t a l p r o ­ cess i n terms of s o l u b i l i t y and a c t i v i t y . Most of the elements of the p e r i o d i c t a b l e can be used i n t h a t type of condensation r e a c t i o n ; a d d i t i o n a l v e r ­ s a t i l i t y i s o f f e r e d by the p o s s i b i l i t y to exchange OR groups q u a n t i t a t i v e l y (again by d i s p l a c i n g e q u i l i b r i u m through d i s t i l l a t i o n ) . Most of the g l a s s y compounds r e s u l t i n g from these r e a c ­ t i o n s have a composition f i t t i n g the above formula, based on elemental and f u n c t i o n a l a n a l y s i s as w e l l as on mass spectrometry. - Characteristic_structural : A more d e t a i l e d anâïysïs~ôf"thësë"prôdûcts~û measurements i n c o n j u n c t i o n with H, C and A 1 NMR spectroscopy has revealed a number of i n t e r e s t i n g s t r u c t u r a l charac­ t e r i s t i c s (15) :they are present i n s o l u t i o n as aggregates l

3

27

η

probably of a g l o b u l a r and thermodynamically favored

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

type

7.

TEYSSIÉ E T A L .

99

Metal-Alcoholate Initiators

of s t r u c t u r e ( u s u a l l y low and i n t e g e r a s s o c i a t i o n number n, from c r y o s c o p i c determinations). The NMR spectra i n ­ d i c a t e of course the presence o f bridged and non-bridged (free) OR groups, and o f A l atoms with a t l e a s t two d i f ­ f e r e n t c o o r d i n a t i o n environments, while e l e c t r o n i c spectra ( v i s i b l e range), i n d i c a t e d i f f e r e n t types o f c o o r d i n a t i o n geometries f o r t r a n s i t i o n metals (blue o r r e d c o b a l t d e r i ­ v a t i v e s ) depending on the nature of the R group (normal or branched). The most i m p o r t a n t s t r u c t u r a l i n d i c a t i o n though i s obtained ( ) from 1 C NMR spectra o f Al ZnOj(On.Bul which r e v e a l an unexpected r i g i d i t y i n these aggregates ? the spectra d i s p l a y indeed broad d i f f u s e resonances not only f o r the α but a l s o the & carbon of the a l k y l groups, r a t h e r u n s e n s i t i v e t o s h i f t reagents, d i l u t i o n and tem­ perature; more narrow bonds (with s l i g h t shift)appear only upon a d d i t i o n o f a l c o h o l s (known t o d i s s o c i a t e the aggre­ gates) , oxiranes o r o b v i o u s l y imply a ver s o l u t i o n , and a number o f s i m i l a r but s l i g h t l y non-equi­ v a l e n t c o o r d i n a t i o n s i t u a t i o n s : the name "tecto-compLexes" i s a c c o r d i n g l y proposed f o r t h i s c l a s s o f compounds, which a l s o e x h i b i t a p a r t i c u l a r e l e c t r o n i c behaviour as put i n evidence by e.p.r. and v i s i b l e -I.R. s p e c t r a . Although t h i s complex s i t u a t i o n probably j u s t i f i e s the amorphous g l a s s y character o f these products, a 1:1 acetato-alkoxide has been c r y s t a l l i z e d ( A l M o (Oi .Pr)^[QAc^ and i t s s t r u c t u r e e s t a b l i s h e d by XR c r y s t a l l o g r a p h y . (16) 6

3

2

2

Polymerization

2

of oxiranes

- The^cataly^st : although most compounds having the composition I n d i c a t e d above i n i t i a t e oxiranes polymeri­ z a t i o n , t h e i r a c t i v i t y as w e l l as the p r o p e r t i e s ( i . e . M.W. and s t e r e o r e g u l a r i t y ) o f the r e s u l t i n g polymers depend c r i t i c a l l y on t h e i r s t r u c t u r a l c h a r a c t e r i s t i c s : these i n c l u d e not only the composition, but a l s o the s i z e (degree o f a s s o c i a t i o n ) and the shape (coordination number and geometry around the metals) o f these c o o r d i n a t i v e l y aggregated compounds. These parameters, obviously d i f ­ f i c u l t t o determine d i r e c t l y and independently, depend i n a very s e n s i t i v e manner on s l i g h t v a r i a t i o n s i n the s y n t h e s i s c o n d i t i o n s , as shown by changes i n k i n e t i c data and product c h a r a c t e r i s t i c s . The ( n . B u O ) A l 0 Z n compound, with a mean degree o f a s ­ s o c i a t i o n η = 6 i n non p o l a r s o l v e n t s i s p a r t i c u l a r l y e f f i c i e n t : the h a l f - p o l y m e r i z a t i o n time o f methyloxirane (MO) i n heptane at 50°C amounts t o 5 minutes (with £MO] = 1M, and[zn}= 10" .M);the r e a g t i o n f o l l o w s a simple 4

2

2

2

obtained. These f e a t u r e s , together with the s t a b i l i t y o f the c a t a l y s t , make o f i t one o f the best candidates f o r a

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

100

p o s s i b l e i n d u s t r i a l production rubbers.

o f high M.W.

polyether

- The_active_groups t h a t p o l y m e r i z a t i o n proceeds by insërtiôn"ïnto~the~Al-OR bonds i s c l e a r l y demonstrated by the f a c t t h a t l i n e a r chains produced c o n t a i n ( a f t e r h y d r o l y s i s ) one OR and one OH end-group. Furthermore, the d i r e c t r e l a t i o n s h i p between the c a t a l y t i c p r o p e r t i e s and a y-oxo-bridged m u l t i n u c l e a r b i m e t a l l i c s t r u c t u r e has been a s c e r t a i n e d by using oxo-alkoxides obtained from h y d r o l y s i s of Meerwein c o m p l e x e s : Al (OR)^· M (OR) :

2

2

2

+ H 0 ^ A 1 M 0 ( O R ) 4 + 2 ROH) : θ ...-CH OCH 2

where 0

V

^ 2

+ 0^

Θ.... .. . - C H O C H O 2

2

N

(4)

i s a monomer molecule or another macromolecule.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

122

More r e c e n t l y one of us with Szymanski observed that the a c t i v e species h o l d i n g monomer molecule can isomerize and the f o l l o w i n g e q u i l i b r i u m was d i r e c t l y observed by 'Hand 13c-NMR i n model compounds (18):

CH -ÇH 2

-

2

CH OCH -yD 5 Jd 2 3

2

C H

L

N

2

0

CH

^

^

N

° CH2° CH -CH 9

CH —CH 9

CH /sJ

0

CH 2

CH OCH — ν, • ^ 3

2

0

^

^-—

ι 2

CH

9

9

z

ffil

v.ix —w ^ 3

ι C

(5)

9

0

9

χ

CH

2

CH

9

CH

9

L

H

2 2

As i n d i c a t e d by the d i r e c t i o n of the arrows the isomeric 7-membered oxonium ion dominates i n the p o l y m e r i z a t i o n of the 5-membered 1,3-dioxolane whereas i n the polymeriza­ t i o n of the 7-membered 1,3-dioxepane c a t i o n a t e d monomer dominates. This i s apparently due to the d i f f e r e n c e s i n s t r a i n o f the i n v o l v e d r i n g s . K i n e t i c a n a l y s i s o f the po­ l y m e r i z a t i o n of these two monomers has shown that the isomeric (enlarged) oxonium ions can be t r e a t e d as the k i n e t i c a l l y dormant s p e c i e s ; propagation and depropagat i o n on these species proceed with almost i d e n t i c a l r a t e s . This explains why f o r the same s t a r t i n g concentration of i n i t i a t o r , as observed by P l e s c h (19), 1,3-dioxepane poly­ merizes over 100 times f a s t e r than~T,3-dioxolane. This i s because the p r o p o r t i o n of the p r o d u c t i v e l y a c t i v e species i s higher f o r the former than f o r the l a t t e r monomer. Covalent

growing species

C l o s e l y r e l a t e d to the i o n i c p o l y m e r i z a t i o n of heterocy­ c l i c monomers i s , what we can c a l l , pseudoionic polymeri­ z a t i o n (or sometimes, perhaps, c r y p t o i o n i c ) . We use the p r e f f i x pseudo- i n the same meaning as i t was f i r s t used i n the v i n y l c a t i o n i c p o l y m e r i z a t i o n . I t means that propagation a c t u a l l y proceeds on the covalent species that could have been i n e q u i l i b r i u m with t h e i r i o n i c counterparts. Several systems f a l l i n g to t h i s category have r e c e n t l y been described f o r both a n i o n i c and c a t i o ­ n i c p o l y m e r i z a t i o n of h e t e r o c y c l i c s . In the a n i o n i c pro­ cesses d e r i v a t i v e s of Zn or A l a l k y l s or a l c o h o l a t e s are b e l i e v e d to f u n c t i o n t h i s way. However, f o r none of these systems the absence of i o n i c c o n t r i b u t i o n was shown. Two c a t a l y t i c systems are of p a r t i c u l a r i n t e r e s t , namely the -Zn-0-ΑΚ systems (_20) and>Al-alkyl modified by bulky porphyrin d e r i v a t i v e s (21). Both are discussed i n t h i s volune and both have been c l e a r l y shown to produce l i v i n g systems. The former with ε-caprolactone and the l a t t e r

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

PENCZEK ET AL.

9.

Structure- Reactivity Relationships

123

with ethylene oxide, propylene oxide and 3 - p r o p i o l a c t o ­ ne (22) . As i n d i c a t e d above, i n the a n i o n i c processes only " e i t h e r - or" s i t u a t i o n was observed, i . e . when covalent species are present no ions i n e q u i l i b r i u m were detected. Covalent a c t i v e species i n the c a t i o n i c p o l y m e r i z a t i o n . In the c a t i o n i c p o l y m e r i z a t i o n s e v e r a l systems were studied, i n which both covalent and i o n i c growth have been simultaneously s t u d i e d . For the f i r s t time the cova­ l e n t growth was described f o r oxazolines by Saegusa ( 2 3 ) . In the p o l y m e r i z a t i o n of THF the presence of cova­ l e n t species was assumed by Smith and Hubin (24) and s h o r t l y a f t e r the covalent species were d i r e c t l y observed i n our l a b o r a t o r y ( H-NMR) (25) as w e l l as by Saegusa 1

1

( 9F-NMR)

Ç26)

and

Pruckmayr~T13c-NMR)

(27).

ÏH-NMR

c l e a r l y showed the existanc covalent and i o n i c , s h i f t s i d e n t i c a l to model compounds. In the p o l y m e r i z a t i o n of h e t e r o c y c l i c monomers, the covalent species i n e q u i l i b r i u m with t h e i r i o n i c counter­ p a r t s were observed d i r e c t l y , thus the corresponding e q u i l i b r i u m constant could be determined f o r polymeri zing systems. There are two r e a c t i o n pathways p o s s i b l e f o r the i o n i z a t i o n r e a c t i o n : .. .-CH 0(CH ) A 2

2

n

(6)

The e x t e r n a l i o n i z a t i o n i n v o l v e s a d d i t i o n of the monomer molecule to the covalent a c t i v e species and, thus, means the covalent propagation. The c o n t r i b u t i o n of each o f the two mechanisms shown i n scheme (6) and operating simultaneously may be estimated on the b a s i s of the dependence of the | i o n | / I e s t e r I r a t i o on conversion. For unimolecular i n t e r n a l r e a c t i o n t h i s p r o p o r t i o n should be independent of mono­ mer c o n c e n t r a t i o n (thus conversion) while f o r the bimolec u l a r , e x t e r n a l i o n i z a t i o n the p r o p o r t i o n of ions should decrease with conversion. I t was shown that f o r the most thoroughly studied system, i . e . p o l y m e r i z a t i o n of THF, the i n t e r n a l i o n i z a t i o n dominates (28). More recent r e s u l t s i n d i c a t e that i n the polymeriza­ t i o n of the 7-membered c y c l i c ether: oxepane (Ox)>both i n t r a - and i n t e r m o l e c u l a r i o n i z a t i o n s have to be

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING

124

POLYMERIZATION

4

1

considered. Thus i n CH3NO2 solvent at 25° 1 ^ = 2 . 3 · 1CT s" and k i=1.35·10-4 mol~i»l»s~1 meaning that both processes proceed with the same rates f o r |0x|=1.7 mol»l"^ ( e f ­ f e c t i v e monomer c o n c e n t r a t i o n ) . For the discussed e a r l i e r THF case the e f f e c t i v e monomer c o n c e n t r a t i o n would be above 100 mol«l~* i . e . much above the c o n c e n t r a t i o n which may be achieved even i n bulk (29). e

R e a c t i v i t i e s of covalent a c t i v e species In the p o l y m e r i z a t i o n o f h e t e r o c y c l i c compounds rate constants of propagation on covalent species were deter­ mined f o r s e v e r a l systems and compared with the c o r r e s ­ ponding r a t e constants of i o n i c growth. In the polymeri­ z a t i o n of THF, k p = 5 « 1 0 - mol-1-l«s-1 i n CH3NO2 at 25°; the s i m i l a r value 3·10" mol~1»l-s-1 was measured i n the Ox p o l y m e r i z a t i o n . Althoug t a n t s of covalent propagatio the c o n t r i b u t i o n of covalent growth i s considerably d i f f e r e n t because the corresponding i o n i c rate constants are d i f f e r e n t : kpi=2.4«10- m o l - ^ l - s " f o r THF and 1.3 · 1 0 ~ mol-1·1·s~1 for Ox. The observed r e l a t i o n s are due to the low s t e r i c requirements of covalent growth and the much l a r g e r r o l e of s t e r i c hindrance f o r i o n i c growth, as discussed by us i n Ref. 13: 4

C

4

2

1

4

Macroion-pairs

and macroions

Below, i n Table III some t y p i c a l data on d i s s o c i a t i o n of the macro- i o n - p a i r s f o r both a n i o n i c and c a t i o n i c r i n g -opening p o l y m e r i z a t i o n are given. There i s a number o f s i m i l a r i t i e s i n behaviour of macroions d e r i v e d from various monomers. Thus, macroion- p a i r s of l i v i n g poly(ethylene oxide) and p o l y c a p r o l a c t o ne i n THF solvent with K ® c a t i o n s , both have very low Κβ. D i s s o c i a t i o n of l i v i n g poly-B-propiolactone, with carbox y l a t e growing anion and crowned K® counterion, i n which e l e c t r o s t a t i c i n t e r e a c t i o n w i t h i n the i o n - p a i r i s much weaker than i n a l c o h o l a t e i o n - p a i r s , resembles t h i s of the t e r t i a r y oxonium i o n s . For both systems i n CH2CI2 solvent Kj) i s approximately equal at 10~5 mol»l"1, i . e . 10 times l a r g e r than f o r a l c o h o l a t e i o n - p a i r s i n THF solvent. ;

5

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

PENCZEK ET AL.

9.

Structure- Reactivity Relationships

125

D i s s o c i a t i o n constants o f some macroion-pairs i n the a n i o n i c and c a t i o n i c ring-opening poly­ merization

Monomer

Growing species

CH CH 0

•·«-CH2CH2O

(CH ).OCO

...-CH CH 0®

1 2

2j

9

9

9

l

2

9

L

..

o

L

D

2

.-CH CH O 2

0

2

...-CH CH O

2



THF

1.8«10~ 30



THF

4.Ί0(200)

Cs®

THF

2.7·10~

0

2

K®/|222|

THF

2.0·10'

C H

2

C 1

2

C H

2

C 1

2

CH CH(CH )S

. . .-CH

CH,CH OCO 1 1

•·»-CH2CH2C^B

K®/DB18C6

^CH ) 0

- Ό

"A

2

3

1C

9

11 ΊΟ

4

7

30 30

3

SbFf

(CH ) 0 6

5·10'

33

5

5

CH N0

2

10

2

2

2

1

mol-r

\

pH CH 0

2

Solvenlt K , 2 5 °

i

CH CH 0

1

2

0

Counter-ion

Réf. Ι

Table I I I .

3·10" (00) _ 2·10-

34

3

2

5

3.1·10~ (0°) _ 35 C H N0 1.6.10" C H

2

C 1

2

3

6

h

...-CH -^ 2



5

2

C H N0 3·10" 6

5

2

2

36

The d i s s o c i a t i o n constants d i s c u s s e d above were determi­ ned from the conductometric data according to Fuoss. The large m a j o r i t y o f the c a t i o n i c processes are w e l l d e s c r i ­ bed by a simple scheme o f i o n - p a i r d i s s o c i a t i o n ; the Κβ determined f o r both the low molecular models and the h i g h polymer f i t t e d with the i o n - p a i r at the end g i v e s i m i l a r r e s u l t s . The high n u c l e o p h i l i c i t y of monomer, s t r o n g l y s o l v a t i n g the c a t i o n , and l a r g e s i z e o f anions decrease the i n t e r a c t i o n w i t h i n the i o n - p a i r i n both thermodynamic and k i n e t i c sense. In the a n i o n i c p o l y m e r i z a t i o n the s i t u a t i o n i s d i f ­ f e r e n t . The negative charges are h i g h l y concentrated at the chain end at l e a s t f o r a l c o h o l a t e and t h i o l a t e anions, a l k a l i metal c a t i o n s u s u a l l y used as counterions have

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING

126

POLYMERIZATION

smaller s i z e , and s t r o n g l y i n t e r a c t with anions. Therefo­ r e , the e l e c t r o s t a t i c a t t r a c t i o n w i t h i n an i o n p a i r i s stronger and KD extremly low. Besides, these i o n - p a i r s are l e e s s u s c e p t i b l e to s o l v a t i o n and s t r o n g l y s e l f - a s s o ­ c i a t e i n t o aggregates. Thus, a n a l y s i s of the f i n e s t r u c ­ ture of ion p a i r s on the bases of Fuoss equation as w e l l as i t s a p p l i c a b i l i t y i n the a n a l y s i s of d i s s o c i a t i o n i s less straightforward than f o r the s o l v a t e d (or solvent separated) i o n - p a i r s . The l a t t e r do not change the degree of s o l v a t i o n i n d i s s o c i a t i o n : 0

...-X®(Mt-nS)®—...-X *

(Mt-nS)

0

(6)

whereas the former may require at l e a s t two d i s c r e t e steps f o r d i s s o c i a t i o n , namely the p r e l i m i n a r y s o l v a t i o n and then d i s s o c i a t i o Fuoss (37) has r e c e n t l of the oTstance between ions f o r such a multistep process may r e q u i r e an approach d i f f e r i n g from the a p p l i c a t i o n of a simple dependence of KD on the d i e l e c t r i c constants or r e c i p r o c a l of the absolute temperature ( i . e . the Fuoss equation). Aggregation of i o n - p a i r s has been demonstrated i n the p o l y m e r i z a t i o n of ethylne oxide (...-CH20OK® i n THF s o l v e n t ) ; apparently c y c l i c trimers of ion p a i r s domina­ t e , formed with the e q u i l i b r i u m constants equal approx. to Ι Ο ^ Ή Ο l - m o l ~ . This value was determined from the a n a l y s i s of the k i n e t i c s of p o l y m e r i z a t i o n (30). Polyme­ r i z a t i o n of ε-caprolactone with Na® as counterion i n THF solvent also shows the 1/3 dependence of the rate of poly­ m e r i z a t i o n on the t o t a l concentration of a c t i v e species (38) whereas with K® counterion p a i r s do not aggregate i n THF (J2)· However i n the p o l y m e r i z a t i o n of l e s s p o l a r dimethyl siloxane trimer (D3) (Na® cation) i o n - p a i r s e f f i c i e n t l y aggregate i n THF (39). The observed concen­ t r a t i o n dependences s t r o n g l y i n H i c a t e the formation aggregates but there are no other more d i r e c t proofs of t h e i r existance. According to Kazanski (40), a l l of the attempts to determine the s t a t e of a s s o c i a t i o n from the v i s c o s i t y measurements have to be considered as unsucces­ s f u l a f t e r c l o s e r examination of the c o n d i t i o n s of measu­ rements and r e l a t e d t h e o r e t i c a l f u n d a m e n t a l s - p a r t i c u l a r l y when the 3/4 law derived f o r concentrated s o l u t i o n s (or polymer melts) i s being a p p l i e d to the d i l u t e s o l u t i o n s i n which polymerization proceeds. Increasing the solvent p o l a r i t y i n both a n i o n i c and c a t i o n i c systems increases s i g n i f i c a n t l y Krj. Thus, Kj) of a l c o h o l a t e macroion-pairs from poly(ethylene oxide) with K® i n DMSO solvent i s equal to 4.7·10" m o l ' l " and Kn i n the p o l y m e r i z a t i o n of THF i n CH3NO2 s o l v e n t equals 10* mol»1" . The same e f f e c t i s observed when i n the anionic poly­ m e r i z a t i o n l a r g e r cations are introduced. P a r t i c u l a r l y when crowned or cryptated cations are used. 7

2

2

2

1

Ί

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

9. PENCZEK ET AL.

Structure-Reactivity Relationships

Macroions and macroion-pairs

127

i n propagation

There are a few systems f o r which, using to e s t a b l i s h proportions of macroion-pairs and macroions, the rate constants of propagation on these species were determined. In the c a t i o n i c p o l y m e r i z a t i o n o f THF, OXP, and more r e ­ c e n t l y conidine, i t has been shown that kp=k^ (_36) · This was explained by assuming weak i n t e r a c t i o n s o f counter­ ions w i t h i n the i o n - p a i r s , due to d i s s i p i t a t i o n of the p o s i t i v e charge i n the onium i o n s , as well as by the stereochemical course of the propagation step (bordeline Sjyj2) i n which the monomer approach hardly requires the p u l l i n g apart o f the anion. Table IV.

Rate constants of propagation i n a n i o n i c poly­ m e r i z a t i o n of h e t e r o c y c l i c compounds Ρ

A c t i v e species mol

3

2

32

2.5·1θ"

3

3.8

32

1

-

32

5.6

32

2.5-ΊΟ"

.-C^CHCCH^^Na® .-CH CH(CH0S^Cs®

2

)

0

. . .-CH^CH(CH^)^ Na |222|

3

32

1.67

Ί.22.10"

6>

9

Ui(CH *- oJ

-

2

1

. . . - C H C H 0 K ® 222 2

32

2

...-CH2CH20®Cs

THF, -30°C

*l*s

4.8-ΊΟ"

... —CH2CH2Û^K THF, 20°C

Ρ

S i (CH ) 2 0 ^ 1 * |211| 3

Réf.

Monomer polymerization conditions

2.3-10" 11.9

32

1.4

Benzene, 20°C (CH f OCO 2

2

CH C1 , 2

2

0

. . .-CH2CH COO K®DB18C6 2

4

7.0·10~

Ί

1.6·10" 33

25°C

(CH^OCO

0

. ..-C(0) ( C H ) O K ® 2

5

4.7

-

31_

THF, 20°C

In the a n i o n i c p o l y m e r i z a t i o n there are three monomers only that have been studied i n more d e t a i l , namely ethy­ lene oxide, propylene s u l f i d e , and 3-propiolactone. Some

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

128

p r e l i m i n a r y data on ε-caprolactone have become a v a i l a b l e more r e c e n t l y . Polymerizations of ethylene oxide and propylene s u l ­ f i d e were reviewed s e v e r a l times by the authors of the o r i g i n a l r e s u l t s , namely the P a r i s and the Moscow groups (32), (40). One of us with Kazanski reviewed r e c e n t l y the recent clata, i n c l u d i n g a l s o p o l y m e r i z a t i o n of lactones (30) . In the p o l y m e r i z a t i o n of ε-caprolactone with K® counterion i n THF propagation proceeds e x c l u s i v e l y on the i o n - p a i r s (31). These i o n - p a i r s p r a c t i c a l l y do not d i s s o ­ c i a t e and do not aggregate at the p o l y m e r i z a t i o n c o n d i t ­ ions (temp, from 0 to 20°, THF, |eCL| =0.5 m o l » l " ) . The comparison of the r a t e constants of propagation on the a l c o h o l a t e i o n p a i r s with K® counterions i n the homopolym e r i z a t i o n of ε-caprolactone_(ki (20°)=4.7 m o l " l s (31) with that of oxirane (k£ (20°)=4.8·10" m o l - · 1 · s " (TZ) r e f l e c t s the muc monomer. Presumably t h i s i s because the higher r i n g s t r a i n of oxirane, i n comparison with that of ε-caprolactone, i s overweighed by the higher r e a c t i v i t y of the e s t e r group i n eCL i n comparison with the r e a c t i v i t y of the ether linkage. 1

o

l e

2

e

1

_ 1

1

S o l v a t i o n phenomena H e t e r o c y c l i c monomers and polymers present i n t h e i r p o l y ­ m e r i z a t i o n s t r o n g l y i n t e r a c t with the growing s p e c i e s . T h i s i s manifested i n f a c t s already d e s c r i b e d i n t h i s paper. C a t i o n i c p o l y m e r i z a t i o n . In the c a t i o n i c p o l y m e r i z a t i o n of c y c l i c ethers, s u l f i d e s , or amines i n CH2CI2 or even i n n i t r o s o l v e n t , monomers and r e s u l t i n g polymers are the most n u c l e o p h i l i c components of the system. Therefore, e x p l a i n i n g equal r e a c t i v i t i e s of macroions and macroion- p a i r s i n the c a t i o n i c p o l y m e r i z a t i o n of h e t e r o c y c l i c monomers, we assumed that both i o n - p a i r s and ions are s o l ­ vated by monomers themselves. This decreases the e l e c t r o ­ s t a t i c i n t e r a c t i o n w i t h i n the i o n - p a i r s . However, more d e t a i l e d a n a l y s i s of ΔΗρ and ASÎ ( a c t i v a t i o n parameters of propagation) revealea that these monomers (at l e a s t THF and oxepane) do not polymerize merely i n c l u s t e r s of mo­ nomer and polymer (8), but that solvent molecules are also present i n the immediate v i c i n i t y of the a c t i v e species (34), (41). This c o n c l u s i o n was based on the f a c t that ΔΗρ and AS^~measured i n various solvent d i f f e r t r e ­ mendously; e.g. AHJj f o r THF i n THF solvent equals 14.0 kcal»mol-' whereas i n THF/CCI4 mixture equals 8.6 k c a l - m o l " . Due to the compensation by the a d j u s t i n g chan­ ges of ASJj the corresponding rate constants measured i n these s o l v e n t d i d not change more than two- three times. 1

Anionic p o l y m e r i z a t i o n . In a n i o n i c p o l y m e r i z a t i o n ethylene oxide, propylene s u l f i d e or t h e i r corresponding

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

PENCZEK ET AL.

9.

Structure- Reactivity Relationships

129

polymers are able to s o l v a t e c a t i o n s . This s t a t e of s o l ­ v a t i o n should d i f f e r with temperature and s i n c e s o l v a t i o n i s exothermic, the lower the temperature the higher the c o n t r i b u t i o n of s o l v a t i o n to the energetics of r e a c t i o n s . Thus, d i s c u s s i n g any c o r r e l a t i o n between s t r u c t u r e and r e a c t i v i t y not only the e l e c t r o n i c and s t r u c t u r a l e l e ments of the a c t i v e species and monomers but also the s o l v a t i o n phenomena should be taken i n t o an account. Below, i n Table V the s o l v a t i o n power of ethylene oxide, propylene oxide, THF, and p o l y ( e t h y l e n e o x i d e ) , M =6000, are compared. n

Table V.

E q u i l i b r i u m constants of complexation of Na ethers and p o l y e t h e r solvents at 25° (30). Ί

1

Ligand ethylene oxide

1

0. 41

propylene

oxide

1

0. 36

THF

1

p o l y ( e t h y l e n e oxide) 6000

6

by

-1

0. 69 3000

The e q u i l i b r i u m constants l i s t e d i n Table V, measured by using N a and Cs-NMR i n d i c a t e that i n the polymeriza­ t i o n of ethylene oxide the Oolymer formed should s t r o n g l y and s e l e c t i v e l y s o l v a t e Na®^counterion. T h i s i s a l s o true f o r K® and Cs®^ c a t i o n s ; the corresponding K f o r p o l y e t ­ hylene oxide) are equal to 500 and 200 1 mol-1. S o l v a t i o n of c a t i o n s by p o l y ( e t h y l e n e oxide) chain i s h i g h l y cooperative, showing the phenomenon "nothing or e v e r y t h i n g , i . e . the c a t i o n i s e i t h e r not s o l v a t e d or f u l l y solvated using i t s complete c o o r d i n a t i o n a b i l i t y : 2 3

133

n

11

X

X ° ο



V.Mt*JÏ2-

M t ® 3 = n

^

/

ι-

0

Mt / 0^

^

0 0



2 CH -0 7

K

P a

4·ΙΟ"

4.5-10" CH -O^CH CH

Ί

4

L

2

ι C H

2

2

>

2

C H

2

CH CH~ 1 s CH CH9

2

2 x

2

CH -Nx 9

1 >" CH -0

C H

?

3 °

On Table V I I I .

Rate constants o f a d d i t i o n o f conidine to various onium i o n s , d i f f e r i n g i n heteroatoms ( C H N 0 s o l v e n t , 35°) (44). 6

5

2

k 1 ,-1 mol »l«s

A c t i v e centre

2

2

CHj^O^" "™ CH -CH 2

0

11

5-10

, CF,S0®

1.10"

2

2

2

2

2

C H ^ S ' " ί" CH -CH CH

2

, SbF®

3

N

3

0

CH,-N.'(9 I CH -CH 2

2

-2

, CF,S0~

9· 10

, CF S0f

7-10"

3

3

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

9.

PENCZEK ET AL.

Structure- Reactivity Relationships

133

The data shown i n Table VIII i n d i c a t e that the higher i s the b a s i c i t y of the parent monomer the lower is the r e a c t i ­ v i t y of a c t i v e species from t h i s monomer toward the standard monomer. Thus the observed order of r e a c t i v i t i e s i n homopropagation i s p a r a l l e l to the order of r e a c t i v i t i e s i n r e a c t i o n of standard monomer with d i f f e r e n t a c t i v e species and reverse to that observed f o r r e a c t i o n of d i f f e r e n t monomers with standard a c t i v e s p e c i e s . This i s a c l e a r demonstration, that i n passing from the ground s t a t e to the t r a n s i t i o n s t a t e the bond-brea­ king i s more advanced than the bond-making. With f u r t h e r s h i f t i n t o the d i r e c t i o n of s t i l l more advanced breaking of the bond w i t h i n a c t i v e species t h i s b o r d e r l i n e SN2 mechanism could e v e n t u a l l y convert i n t o the Sfl1 mechanism. This should be promoted by the presen­ ce of the s t a b i l i z i n nium i o n ( l i k e i n c y c l i high ring s t r a i n ( l i k e i n the three membered r i n g s ) . Indeed, c o n t r i b u t i o n of Sj^l mechanism i n both cases has been p o s t u l a t e d f o r p o l y m e r i z a t i o n of 1,3-dioxolane and isobutylene oxide but there i s s t i l l no c l e a r - c u t e v i ­ dence f o r i t s o p e r a t i o n . C a t i o n i c p o l y m e r i z a t i o n of h e t e r o c y c l i c monomers can proceed not only by the S^2 mechanism i n v o l v i n g onium ions l o c a t e d at the chain end, and analysed i n t h i s paper, but also by another S^2 mechanism i n v o l v i n g a c t i v a t e d monomer, adding to the n e u t r a l chain ends. For the l a t t e r no c o r r e l a t i o n i s yet a v a i l a b l e and can d i f f e r from these described f o r onium ions i n t h i s s e c t i o n . Literature Cited 1. Bamford, C.H.; Barb, W.G.; Jenkins, A.D.; Onyon, P.F. "The K i n e t i c s of V i n y l P o l y m e r i z a t i o n by R a d i c a l Mechanism"; Butterworths: London, 1958. 2. Bagdasarian, K.S. "Theory of R a d i c a l P o l y m e r i z a t i o n " (in Russian); AN SU: Moscow 1959. 3. Penczek, S.; Kubisa, P.; Matyjaszewski, K.; Szymanski, R. In " C a t i o n i c P o l y m e r i z a t i o n " ; Goethals, E . J . , Ed.; Academic: i n p r e s s . 4. Morton, M.; Kammereck, R.F.; F e t t e r s , L . J . Br.Polym.J. 1971, 3, 120. 5. Duda, Α.; Sosnowski, S.; Słomkowski, S.; Penczek,S. Makromol.Chem., submitted. 6. Brzezinska, K.; Chwiałkowska, W.; Kubisa, P.; Matyjaszewski, K.; Penczek, S. Makromol.Chem. 1977, 178, 2491. 7. Matyjaszewski, K.; Penczek, S. Makromol.Chem. 1981, 182, 1735. 8. Szwarc, M. Adv.Polym.Sci. 1983, 49, 1. 9. Saegusa, T.; Matsumoto, S. J.Polym.Sci. 1968, 6, 1559. 10. Barzykina, R.G.; Komratov, G.N.; Korovina, G.V.; E n t e l i s , S.G. Vysokomol.Soed. 1974, 16, 906.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

134

RING-OPENING POLYMERIZATION

11. Sawamoto, M.; Furukawa, Α.; Higashimura, T. Macromolecules 1983, 16, 518. 12. Hofman, Α.; Szymanski, R.; Słomkowski, S.; Penczek,S. Makromol.Chem. in press. 13. Penczek, S.; Kubisa, P.; Matyjaszewski, K. Adv.Polym. Sci. 1980, 37, 1. 14. Hofman, Α.; Słomkowski, S.; Penczek, S. Makromol.Chem. 1984, 185, 91. 15. Jedlinski, Z.; Kasperczyk, J.; Dworak, Α.; Matuszewska, B. Makromol.Chem. 1982, 183, 587. 16. Szymanski, R.; Kubisa, P.; Penczek, S. Macromolecules 1983, 16, 1000. 17. Matyjaszewski, K. J.Polym.Sci.,Polym.Chem.Ed. 1984, 22, 29. 18. Szymanski, R.; Penczek, S. Makromol.Chem. 1982, 183, 1587. 19. Plesch, P.H.; Westermann 3837. 20. Ouhadi, T.; Hamitou, Α.; Jerome, R.; Teyssie, P. Macromolecules 1976, 9, 927. 21. Aida, T.; Inoue, S. Macromolecules 1981, 14, 1162. 22. Yasuda, T.; Aida, T.; Inoue, S. Macromolecules 1983 16, 1792. 23. Saegusa, T. Makromol.Chem. 1974, 175, 1199. 24. Smith, S.; Hubin, A.J. J.Macromol.Sci.-Chem. 1973, A7, 1399. 25. Matyjaszewski, K.; Penczek, S. J.Polym.Sci.,Polym. Chem.Ed. 1974, 12, 1905. 26. Kobayashi, S.; Danda, H.; Saegusa, T. Macromolecules 1974, 7, 415. 27. Pruckmayr, G.; Wu, T.K. Macromolecules 1975, 8, 954. 28. Buyle, A.M.; Matyjaszewski, K.; Penczek, S. Macromolecules 1977, 10, 269. 29. Baran, T.; Brzezinska, K.; Matyjaszewski, K.; Penczek, S. Makromol.Chem. 1983, 184, 2497. 30. Kazanskii, K.S.; Penczek, S. Vysokomol.Soed. 1983,25 1347. 31. Sosnowski, S.; Słomkowski, S.; Penczek, S. J.Macromol. Sci.-Chem.in press. 32. Boileau, S. ACS SYMPOSIUM SERIES No. 166, Mc Grath, J.E. Editor,American Chemical Society: Washington, D.C., 1981; p. 283. 33. Słomkowski, S.; Penczek, S. Macromolecules 1980, 13, 229. 34. Matyjaszewski, K.; Słomkowski, S.; Penczek, S. J.Polym.Sci.,Polym.Chem.Ed. 1979, 17, 2413. 35. Brzezinska, K.; Matyjaszewski, K.; Penczek, S. Makromol.Chem. 1978, 179, 2387. 36. Matyjaszewski, K. Makromol.Chem. 1984, 185, 51. 37. Fuoss, R.M. J.Amer.Chem.Soc. 1978, 100, 5576. 38. Sosnowski, S.; Słomkowski, S.; Penczek, S.; Reibel, L. Makromol.Chem. 1983, 184, 2159. 39. Chojnowski, J.; Mazurek, M. Makromol.Chem. 1975, 176, 2999.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

9.

PENCZEK ET AL.

Structure-Reactivity Relationships

135

40. K a z a n s k i i , K.S. Pure & Appl.Chem. 1981, 53, 1645. 41. Penczek, S. Macromolecules l979, 12, 1010. 42. A r k h i p o v i t c h , G.N.; Dubravskii, S.A., K a z a n k i i , K.S.; Shupik, A.N. Vysokomol.Soedin. 1981, 23, 1653. 43. Dimov, D.K.; Panayotov, I.M.; Lazarov, V.N., Tsvetanov J. Polym.Sci.,Polymer Chem.Ed. 1982, 20, 1389. 44. Matyjaszewski, K.; Penczek, S. Macromolecules, submitted. RECEIVED November 15, 1984

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

10 Control of Ring-Opening Polymerization with Metalloporphyrin Catalysts Mechanistic Aspects SHOHEI INOUE and TAKUZO AIDA Department of Synthetic Chemistry, Faculty of Engineering, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan

Aluminum porphyrin initiator (catalysts) d particularly in ring-openin products with well-define narrow distribution. The reaction can be extended to the polymerization of epoxide andβ-lactone,and the copolymerization of epoxide with carbon dioxide and with cyclic acid anhydride. The formation of a copolymer with narrow molecular weight distribution from epoxide and cyclic acid anhydride i s of interest because of the two different propagating species involved: an alkoxide and a carboxylate. An aluminum porphyrin coupled with a quaternary ammonium or phosphonium salt i s a good catalyst system for the alternating copolymerization of epoxide and carbon dioxide or epoxide and cyclic acid anhydride. The latter reaction i s the first example of a catalytic process occurring on both sides of a metalloporphyrin plane. Aluminum porphyrins are i n i t i a t o r s (catalysts) used p a r t i c u l a r l y i n ring-opening polymerization to y i e l d products of well-defined molecular weight and with narrow d i s t r i b u t i o n . The reaction has been extended from the polymerization of epoxide (J_) to that of /3-lactone (2) , and also to the copolymerization of epoxide and carbon dioxide (3) or epoxide and c y c l i c acid anhydride (4). Because of the l i v i n g nature of the polymerization, block copolymerization from d i f f e r e n t epoxides, f o r example, has been accomplished with high e f f i c i e n c y (5). Every aluminum atom i n the metalloporphyrin c a r r i e s one growing polymer molecule i n the polymerization of epoxide and/3-lactone. This fact and the strong e f f e c t of the r i n g current of porphyrin on NMR spectrum are of great advantage for the i n v e s t i g a t i o n of the structure of the growing species and the r e a c t i v i t y .

0097-6156/ 85/ 0286-0137506.00/ 0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

138

RING-OPENING POLYMERIZATION

1 a b c d e

X=C1 X=OR X=0 CR X=OAr 2

X—C2H5

TPPAl-X

Structure and Reactivity of Growing Species i n the Polymerization of Epoxide The growing species i n th tetraphenylporphinatoaluminum chloride (TPPA1C1, 1a) i s a porphinatoaluminum alkoxide (1b) (6). The 1H-NMR spectrum of the reaction mixture i n the polymerization of propylene oxide shows a doublet signal at an unusually high magnetic f i e l d (-2.0 ppm). This signal i s due to the methyl group at the growing end attached to the metalloporphyrin (Figure 1 ) .

(1) TPPA1C1

Polymerization of ethylene oxide proceeds s i m i l a r l y to give TPPA1-0-CH2-CH2- as the growing end; a c h a r a c t e r i s t i c signal i s shown at -1.4 ppm (Figure 2). On the other hand, tert-butylethylene oxide reacts with TPPA1C1 to give the corresponding alkoxide, TPPA1-0-CH {C(CH3)3}-CH2-C1 (-1.55 ppm); further propagation reaction proceeds with d i f f i c u l t y . By taking advantage of this fact, the r e a c t i v i t y of porphinatoaluminum alkoxide as the growing species can be evaluated: In the reaction o f tert-butylethylene oxide with an equimolar mixture of the l i v i n g ends from ethylene oxide and from propylene oxide, the porphinatoaluminum alkoxide corresponding to tert-butylethylene oxide increased at the expense of the l i v i n g end from ethylene oxide, whereas the l i v i n g end from propylene oxide remained almost i n t a c t . Thus, TPPA1-0-CH2-CH2- i s concluded to be much more reactive towards epoxide than TPPAl-0-CH(CH3)-CH2-. Structure of Growing Species i n the Polymerization of ^-Lactone In the ring-opening reaction of 0-lactone, two d i f f e r e n t modes of cleavage are possible. One i s the cleavage at the alkyl-oxygen bond to give a porphinatoaluminum carboxylate (Equation 2a), and the other i s acyl-oxygen bond s c i s s i o n to form a porphinatoaluminum alkoxide carry­ ing an acyl chloride group (2b).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

10.

INOUE A N D AIDA

1 9

' 8

Polymerization with Metalloporphyrin Catalysts

' 7

Figure 1. 1H-NMR spectrum of a l i v i n g oligomeric propylene oxide prepared with TPPA1C1. (Reproduced from Ref. 6. Copyright 1981 American Chemical Society.)

9

8

7

Figure 2. 1H-NMR spectrum of a l i v i n g oligomeric ethylene oxide prepared with TPPA1C1. (Reproduced from Ref. 6. Copyright 1981 American Chemical Society.)

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

139

RING-OPENING POLYMERIZATION

140

f

(A1-C1 _Z

(a) ^

(A1-0-C-CH -CH-C1

(2a)

2

^

^

Λ

(b)

"

I Al-0-CH-CH -C-Cl

(2b)

2

R = Η or CH

3

In the IR spectrum of the equimolar reaction product of0-propiolactone and TPPA1C1, a strong absorption bond due to the carboxylate group was observed at 1600 cm (Figure 3). However, the absorption due to the acyl chloride group at 1800 cm-1 was not seen. The 1H-NMR spectrum of this reaction product i s characterized by a t r i p l e t signal at -0.7 ppm, from protons of the methylene group of a porphinatoaluminum carboxylate (2a, R=H) (Figur tone took place at the acyl-oxyge from the TPPA1-0-CH2-CH2- group should appear at -1.4 ppm, s i m i l a r l y to the species from ethylene oxide. The 1H-NMR spectrum of the equi­ molar reaction product of TPPAlEt (1e) and 3-chloro-propionic acid was i d e n t i c a l to the spectrum of the TPPAlCl-propiolactone system.

^ Ql-0-C-CH -CH -Cl

Ql-Et + H-0-C-CH -CH -Cl 2

2

2

0

+ EtH

2

(3)

0

Thus, the ring opening of /3-propiolactone takes place almost exclusively at the alkyl-oxygen bond to form a porphinatoaluminum carboxylate (Equation 2a) (7). The same conclusion was obtained f o r the oligomerization of /3-propiolactone and /3-butyrolactone as a result of 1H-NMR and 13C-NMR spectroscopy. As expected, the equimolar reac­ t i o n product o f TPPAlEt (le) and carboxylic acid ( c f . Equation 3) i s a good i n i t i a t o r f o r the polymerization of/3-lactone and yields a polymer with narrow molecular weight d i s t r i b u t i o n . Copolymerization o f Epoxide with C02, and Epoxide with Cyclic Acid Anhydride TPPA10R (1b) was e f f e c t i v e f o r the copolymerization o f epoxide with C02 (8-9) or with c y c l i c acid anhydride and produced copolymers with ester and ether linkages. These copolymers have a narrow molecular weight d i s t r i b u t i o n , but do not y i e l d alternating structures. J3H

CH

3

CH -CH

+

2

C0

CH

3

3

^ -ÎO-iH-CHaA-^O-C-O-CH-CHaV \ Λ \ il Λ-χ

2

\ / o

(4)

N

CH 2

o'

CH

(o)

3

CH -CH + _ /

\y

\

_

Cy

3

-CoJm-Œ XCo-Ç 2

0

CH

3

C-0-CH-CH X 2

0

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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141

Figure 3. IR spectrum o 0-propiolactone. (Reproduced from Ref. 7. Copyright 1983 American Chemical Society.)

Porphyrin

CI-CH2-CH2-C-O—Al

-1

-2 (ppm)

Figure 4. 1H-NMR spectrum of the equimolar reaction product of TPPA1C1 andβ-propiolactone. (Reproduced from Ref. 7. Copyright 1983 American Chemical Society.)

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

142

RING-OPENING POLYMERIZATION

This r e s u l t i s p a r t i c u l a r l y interesting because the propagation i s presumed to involve two d i f f e r e n t types of reactions occurring on the same aluminum atom ( i . e . , the reaction of aluminum alkoxide with C02 or c y c l i c acid anhydride and the reaction o f aluminum carboxylate with epoxide). Aluminum Porphyrin Coupled with Ammonium or Phosphonium Salt In order to enhance the r e a c t i v i t y of aluminum porphyrins Q ) , espe­ c i a l l y towards C02 i n the copolymerization with epoxide (Equation 4), the e f f e c t of addition of an amine or phosphine as a possible sixth ligand to the aluminum porphyrin was examined. The enhancement i n r e a c t i v i t y by the addition of a t e r t i a r y amine such as N-methylimidazole was actually observed for the epoxide-C02 reaction. The product, however, was a c y c l i c carbonate (JJ)), not a linear copolymer. On the other hand, .the addition of triphenylphosphine was very e f f e c ­ t i v e i n the formation o C02, or from epoxide an studies indicated that triphenylphosphine was converted to a quater nary s a l t i n the reaction, the e f f e c t of a quaternary phosphonium or ammonium s a l t separately prepared was examined. As a result of t h i s investigation, the system containing an aluminum porphyrin and phos­ phonium or ammonium s a l t was found to be a novel, e f f e c t i v e catalyst for these alternating copolymerization reactions and to y i e l d products with narrow molecular weight d i s t r i b u t i o n . For example, the alternating copolymerization of propylene oxide and phthalic anhydride (Equation 5, χ = 0) with the TPPAlCl-ethyltriphenyl-phosphonium bromide (EtPh3PBr) system proceeds at room temperature (Figure 5) much more readily than with other catalysts ( V p . The molecular weight of the product increased l i n e a r l y with conversion, and the narrow molecular weight d i s t r i b u t i o n was retained (Figure 6). TPPAlCl-tetraalkylammonium halide and TPPA102CR-tetraalkylammonium carboxylate (R4N02CR) systems are also e f f e c t i v e . Tetraalkylammonium or phosphonium s a l t alone i s i n e f f e c t i v e under similar conditions. Catalytic Reaction on Both Sides of a Metalloporphyrin Plane Of p a r t i c u l a r interest i s the fact that i n the alternating copolymerization of epoxide and phthalic anhydride with the TPPAlCl-EtPh3PBr system every aluminum atom of the catalyst carries two growing polymer molecules. As seen i n Table I, the observed molecular weight of the copolymer, determined by vapor pressure osmometry (VPO), i s about one-half the molecular weight calculated on the assumption that every aluminum atom c a r r i e s one polymer molecule. In this connection, i t i s important to note that with the TPPA102CR and R4N02CR system, the catalyst system for this copolymerization, a novel porphinatoaluminum complex with two carboxy­ l a t e a x i a l ligands i s formed.

(6)

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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Polymerization with Metalloporphyrin Catalysts

0

143

2 time in hr

Figure 5. Alternating copolymerization of propylene oxide (PO) and phthalic anhydride (PA) with the TPPAlCl-Et3PhPBr system. [P0] = [PA]/ [Cat] = 25, i n CH2C12 at room temperature.

conversion in ·/·

Figure 6. The influence of conversion on molecular weight i n the alternating copolymerization of propylene oxide and phthalic anhydride catalyzed by the TPPAlCl-Et3PhPBr system.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

144

The formation of a s i m i l a r porphinatoaluminum complex was observed i n the copolymerization of propylene oxide and phthalic anhydride with the TPPA102CCMe3-Et4N02CMe system. In the 1H-NMR spectrum of the reaction mixture, we observed that the signals assigned to the phthalate group attached to porphinatoaluminum were shifted to a higher magnetic f i e l d (Figure 7a). Their intensity values are estimated to be twice that of the signal due to the porphyrin ligand. Thus, Equation 7 i s suggested as a possible mechanism for the copolymerization proceed­ ing on both sides of a metalloporphyrin plane, where both X and Y groups, corresponding to Me3CC02- and MeC02- groups, respectively, i n this reaction, can i n i t i a t e the reaction. 0

0

Al-X

RJ?

+

+

y

@q

+

/

Y-C-C-0 vwv\ C0 ---|^A1- - - 0 C 2

2

(R*N)

ΛΛΛΛΛ

O-C-C-X

(7)

+

More evidence i n favor of polymer chain growth on both sides of a metalloporphyrin plane was obtained i n the copolymerization of propylene oxide and phthalic anhydride. The catalyst was the combina­ tion of EtPh3PBr and TPPAl-(-0-CHMe-CH2-)-Cl (TPPA1PP0), which can be obtained by the polymerization of propylene oxide with TPPA1C1 (Equa­ t i o n 1). I f the copolymerization proceeds on both sides of a metal­ loporphyrin plane, a block copolymer, polyetherpolyester, i s expected to be formed on one side, and a polyester i s expected on the other side. In fact, GPC of the reaction product (Figure 8) showed two narrow peaks and c l e a r l y indicated the formation of polymers with d i f f e r e n t chain lengths. Thus, t h i s reaction provides the f i r s t example of a c a t a l y t i c reaction occurring on both sides of a metal­ loporphyrin plane.

Table I,

Alternating Copolymerization of Epoxide and Phthalic Anhydride with TPPAlCl-EtPh PBr System 3

a)

Epoxide R CH CH CH

R

Μ χ1(Γ η

?

VP0

Η CH (cis) CH (trans)

3

3

2.97 3.25 3.39 4.00 2.71 3.60

3

3

3

(CH ) Ph Η Ph0CH Η 2

A

2

a)

f

RHC-CHR

b)

3

M /M w η GPC 1.09 1.11 1.09 1.17 1.14 1.08

M

N/Al

1 cale

for 5.15 N/A1=1 5.50 5.50 6.15 6.70 7.45

b)

(ïï . /M ) cale η 1.74 1.69 1.62 1.54 2.47 2.07

N: Number of polymer molecules

Y In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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' 10

9

8

Polymerization with Metalloporphyrin Catalysts

• 7

» 6

• 5

ι 4

ι

ι

ι

ι

ι

ι

3

2

1

0

-1

-2

145

ι

-3 (6,ppm)

Figure 7. 1H-NMR spectrum of the copolymerization of propylene oxide and phthalic anhydride with the TPPA102CCMe3-Et4N02CMe system ( i n CDC13 at room temperature).

- —

high m.w.

Figure 8. GPC p r o f i l e of the copolymerization of propylene oxide and phthalic anhydride with the TPPAlPP0-EtPh3PBr system. Key: , the product; and , TPPA1PP0. In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING

146

POLYMERIZATION

Acknowledgment The author i s grateful to Messrs. T. Yasuda, M. Ishikawa, and K. Sanuki for their collaboration.

Literature Cited 1. Aida, T.; Mizuta, R.; Yoshida, Y.; Inoue, S. Makromol. Chem., 1981, 182, 1073. 2. Yasuda, T.; Aida, T.; Inoue, S. Makromol. Chem., Rapid Commun., 1982, 3, 585. 3. Aida, T.; Inoue, S. Macromolecules, 1982, 15, 682. 4. Aida, T.; Inoue, S. Polymer Preprints Japan, 1983, 32, 217-218. 5. Aida, T.; Inoue, S. Macromolecules, 1981, 14, 1162. 6. Aida, T.; Inoue, S. Macromolecules, 1981, 14, 1166. 7. Yasuda, T.; Aida, T.; Inoue, S. Macromolecules, 1983, 16, 1792. 8. Aida, T.; Inoue, S 9. Inoue, S.; Yamazaki of Carbon Dioxide"; Kodansha : Tokyo, 1981; p. 167. 10. Aida, T.; Inoue, S. J. Am. Chem. Soc., 1983, 105, 1304. 11. Ishii, Y.; Sakai, S. In "Ring-Opening Polymerization"; Frisch, K. C.; Reegen, S. L., Eds.; Marcel Dekker: New York, 1969; p. 91. RECEIVED October 4, 1984

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

11 Anionic Ring-Opening Polymerization of Octamethylcyclotetrasiloxane in the Presence of 1,3-Bis(aminopropyl)-1,1,3,3-tetramethyldisiloxane 1

P. M. SORMANI, R. J . MINTON , and J A M E S E. McGRATH Department of Chemistry and Polymer Materials and Interfaces Laboratory, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Polyorganosiloxanes ar class of "semi-inorganic interesting and useful properties exhibited by these materials that make them worthy of study. For example, they exhibit high l u b r i c i t y , low glass t r a n s i t i o n temperatures, good thermal s t a b i l i t y , high gas permeability, unique surface properties, and low t o x i c i t y (1). Cyclic organosiloxanes and s i l a n o l oligomers may be readily prepared by the hydrolysis of chlorosilanes, according to Scheme 1 (1). The predominant c y c l i c s are those corresponding to x=4 or 5, while the strained c y c l i c trimer i s present only i n small quantities. RR'SiCl

2

+ 2H 0 2

-->

[RR'Si(OH) ] + 2HCl 2

Scheme 1. Preparation of c y c l i c organosiloxanes and chlorosilanes.(1) Polydimethylsiloxane oligomers may be easily prepared by the acid or base catalyzed ring opening polymerization of the c y c l i c tetramer, octamethylcyclotetrasiloxane. The molecular weight of the polymer prepared may be controlled by the addition of a linear disiloxane as an endblocker (2,3,4). When the disiloxane i s hexamethyldisiloxane, this i s the well-studied case of the 1

Current address: Thoratec Laboratories, 2023 Eighth Street, Berkeley, C A 94710

0097-6156/ 85/0286-0147506.00/ 0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

148

preparation of silicone oil. However, it is the case of functional disiloxanes that has been of interest in our laboratories for quite some time (3,5). Table I shows a l i s t of the various functional disiloxanes that have been used to prepare functionally terminated siloxane oligomers (6). Scheme II shows a general outline for the preparation of these oligomers. It should be noted that in the absence of any endblocker, a high molecular weight silicone gum is formed. Table I End blockers used to prepare functionally-terminated polysiloxane oligomers CH [H N 2

3

(-CH )3Si]-0 I 2

2

CH

3

CHo CHo I I (CH ) N-[Si-0]—Si-N(CH ) I I CH CH 0 CH 3

2

3

low molecular weight silylamine end blocker

2

x

3

[ΗΝ

3

3

^K-(CH ) NHC-(CH ) -Si-]-0 ' I 2 CH 2

>

2

2

3

piperazine-terminated disiloxane

3

0

CH

3

α, ω carboxypropyl 1,3 tetramethyldisiloxane

[HOC-(CH ) -Si-]-0 I 2 CH 2

3

3

CH [CH

2

3

CH-CH -0(CH ) -S i ] - 0 2

2

3

CH

α, ω glycidoxypropyl 1,3 tetramethyldisiloxane

3

These ring-opening polymerizations are referred to as e q u i l i b r a t i o n reactions. Since a variety of interchange reactions can take place, a quantitative conversion of the tetramer to high polymer i s not achieved and there i s , at thermodynamic equilibrium, a mixture of linear and c y c l i c species present. Scheme III shows examples of the types of r e d i s t r i b u t i o n reactions thought to be occurring i n these systems. It i s generally convenient to use "D" to refer to a difunctional siloxane unit and "M" to refer to a monofunctional siloxane unit. Thus, D4 represents the c y c l i c siloxane tetramer and MM represents the linear hexamethyldisiloxane.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

11.

SORMANI E T A L .

CH CH I I R-Si-O-Si-R I CH3 CH 3

Anionic Polymerization of Octamethylcyclotetrasiloxane

3

CH CH3 1 CH3 | I I • R-Si-0 S1-0--S1-R 3

c a t a l y s t , heat +

D4 argon

CH

3

Scheme I I .

3

+ cyclics

xl

U CH

CH

3

3

Preparation of functional siloxane oligomers. functional group l i s t e d in Table I .

R = any

This terminology normally applies only to dimethylsiloxy u n i t s . I t should be noted that with the exception of using organolithium catalysts i n the anionic polymerization of the D c y c l i c , s i g n i f i c a n t amounts of r e d i s t r i b u t i o n cannot be avoided (7_,8). 3

(1)

-D - + D

(2)

-D - +

(3)

MD M + MM

(4)

MD M + MDyM

x

— •

-D

-

x

X

X

• MD _5)M + MD5M (x

• MD

(x+w

) M + MD( _ )M y

w

Scheme I I I . Redistribution reactions occurring during a siloxane equilibration. There are a variety of catalysts that can be used i n the preparation of polysiloxane oligomers by e q u i l i b r a t i o n reactions. The choice of catalyst depends upon the temperature of the e q u i l i b r a t i o n as well as the type of functional disiloxane that i s used. For example, i n preparing an aminopropyl terminated siloxane oligomer, a basic catalyst i s used, rather than an acidic catalyst which would react with the amine end groups. The discussion here w i l l be limited to basic c a t a l y s t s . Bases such as hydroxides, alcoholates, phenolates and siloxanolates of the a l k a l i metals, quaternary ammonium and phosphonium bases and the corresponding siloxanolates and f l u o r i d e s , and organoalkali metal compounds have a l l been found to catalyze the polymerization of c y c l i c siloxanes (1,2,9,10). I t i s believed that a l l catalysts generate the siloxanolate anion i n s i t u , and i t i s t h i s species which breaks the silicon-oxygen bond in either the linear or c y c l i c siloxanes present. However, the r e a c t i v i t i e s of the disiloxane and the various c y c l i c siloxanes d i f f e r . The rate of reaction increases i n the order MM < MDM < MD M < D4 < D , where MM again represents hexamethyldisiloxane, a non-functional endblocker. Catalysts based on the quaternary ammonium and phosphonium bases are referred to as transient catalysts, since they decompose above certain temperatures to products which are not c a t a l y t i c a l l y active toward siloxanes. An example of this i s the tetramethylammonium siloxanolate catalyst, prepared by the reaction of t e t r a methylammonium hydroxide with D4 (11). This catalyst polymerizes D4 at temperatures up to perhaps 120°C. Above this temperature, the catalyst f a i r l y rapidly decomposes to trimethyl amine and methoxyterminated siloxane. 2

3

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RING-OPENING

150

POLYMERIZATION

However, catalysts such as the potassium siloxanolate catalyst are not transient. Non-transient catalysts must be neutralized or removed by some other method in order to give a thermally stable polymer. If the catalyst i s not removed, i t w i l l cause depolymerization at high temperatures. For example, a s i l i c o n e gum prepared by reacting D4 with 0.01% KOH has been reported to lose over 99% of i t s weight at 250°C i n 24 hours (11). Non-transient catalysts can often be used at much higher temperatures than the transient catalysts, leading, of course, to faster rates of reaction. The kinetics of these processes have been of interest to a number of workers (12). However, there has been no investigation of these e q u i l i b r a t i o n reaction kinetics using functional endblockers. Studies have been done on the kinetics of formation of s i l i c o n e gum or the reaction of D4 with hexamethyldisiloxane. For example, Grubb and Osthoff studied the kinetics of the KOH catalyzed polymerization of D (12). It was found that th proceeds according to f i r s t order k i n e t i c s , with a square root dependence on the catalyst concentration. The square root dependence on the catalyst concentration i s believed to be due to the existence of an equilibrium between an active ion pair and a an inactive associated form (-SiOM)2» Rate constants were determined at different catalyst levels and temperatures. An a c t i v a t i o n energy of about 18 kcal/mole was determined by an Arrhenius plot, i n agreement with other workers i n the f i e l d (9). It i s important to consider the effect of solvent on the rate of polymerization as well as on the amount of c y c l i c s that are present. The rate of polymerization can be greatly enhanced by the action of dipolar aprotic solvents such as DMSO. This has been demonstrated by Cooper (13). However, the presence of a solvent w i l l also increase the amount of c y c l i c s present i n a f u l l y equilibrated sample. This can be understood in a qualitative way by considering that the siloxanolate species can attack not only silicon-oxygen bonds i n the c y c l i c s present, but also a phenomenon known as back-biting can occur. Back-biting refers to the attack of the siloxanolate anion on a silicon-oxygen bond along the same chain at least four repeat units away. Scheme IV gives an i l l u s t r a t i o n of this as well as other types of reactions occurring. When the siloxanes present are diluted by the presence of a solvent, the siloxanolate anion w i l l be less l i k e l y to encounter a c y c l i c to attack, and so back-biting w i l l become more prevalent. There i s , i n f a c t , a c r i t i c a l concentration, above which only c y c l i c molecules w i l l e x i s t . Generally therefore, i t i s more desirable to perform these e q u i l i b r a t i o n reactions i n bulk, and so l i m i t the formation of c y c l i c species as much as possible. There have been a variety of a n a l y t i c a l techniques used to study these e q u i l i b r a t i o n reactions. For example, gel permeation chromatography (GPC), or size exclusion chromatography (SEC), and gas-liquid chromatography (GLC) have been useful techniques (5,14). While GPC i s useful for monitoring the overall molecular weight d i s t r i b u t i o n of the polysiloxane, there are some l i m i t a t i o n s . For example, aminopropyl-terminated polysiloxane oligomers cannot be run on styragel based SEC columns due to adsorption of the oligomer on 4

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

11.

SORMANI ET AL.

Anionic Polymerization ofOctamethylcyclotetrasiloxane

the column. Either a silanized s i l i c a gel-based column must be used, or the oligomer must be derivatized. In addition to these problems, while GPC can be used to monitor the disappearance of D4 as the e q u i l i b r a t i o n proceeds, i t does not address the question of whether or not the functional disiloxane has been quantitatively consumed·

ΘΦ M CH

3

1 -Si-O1 1 CHo

η

R-Si-O-Si-R I I CH CH

Terminated

Θ®

Μ

^

0® —0

New Chain

growing chain

3

CH

O-Si-R I CH

M

Catalyst or other growing chain

3

3

3

CH

3

I ΘΘ + R-Si-0 M I CH

3

I "BACKBITING"

Θ®

0

M

+ Cyclics

Scheme IV.

Possible reactions occurring during a siloxane equilibration.

Gas-liquid chromatography has the potential to discriminate between the different oligomeric species formed. We have found that c a p i l l a r y GC may be used to measure the concentration of α, ω aminopropyl 1,3 tetramethyldisiloxane i n e q u i l i b r a t i o n reactions. Although the presence of catalyst could p o t e n t i a l l y lead to the generation of additional c y c l i c s at the elevated temperatures necessary for GC, there was no effect on the amount of disiloxane present. Of course, to measure the D4 concentration, the samples must be free of c a t a l y s t .

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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RING-OPENING POLYMERIZATION

152

High-Performance Liquid Chromatography (HPLC) has been used for the analysis of oligomers (15,16). A clear advantage of HPLC i s that the analysis can be done at room temperature, thus eliminating the p o s s i b i l i t y of generating additional reaction products such as c y c l i c s . HPLC has therefore been of use i n measuring the amount of D4 present as the e q u i l i b r a t i o n reaction proceeds, as well as i n observing the appearance of new oligomeric species. This paper w i l l discuss investigations of the polymerization of D4 i n the presence of α, ω aminopropyl 1,3 tetramethyldisiloxane with potassium siloxanolate c a t a l y s t . The effects of temperature and catalyst concentration on the rate of disappearance of both starting materials w i l l be discussed. Demonstration of the u t i l i t y of both non-aqueous reversed-phase HPLC and c a p i l l a r y GC for the investigation of these reactions w i l l be presented. Experimental A.

Catalyst Preparatio

The catalyst used i n this work was prepared either i n bulk or using toluene as an azeotroping agent. Octamethylcyclotetrasiloxane, D4, and potassium hydroxide (KOH) were used as received. The KOH was crushed into a fine powder and added to enough D4 to make a mixture with a molar r a t i o of D4 to KOH of 10/1 i n the case of the bulk c a t a l y s t . This corresponds to 2 wt% KOH. The mixture was then put into a flask equipped with an argon i n l e t , an overhead s t i r r e r , an attached Dean-Stark trap, with a condenser attached to the Dean-Stark trap. Argon was bubbled through the mixture with s t i r r i n g , and the mixture was heated to 120°C. The high temperature and argon stream were necessary to eliminate water present i n the base as well as any water formed during the reaction. As the KOH reacted with the D4, the mixture gradually became more viscous. After a l l the KOH had dissolved, the mixture was s t i l l transparent and c o l o r l e s s . In general, within 12 hours, the mixture was a milky white, viscous material. After approximately 24 hours, the mixture was clear and colorless and able to be removed by pipet. T i t r a t i o n s of the catalysts were performed on a Fischer automatic t i t r a t o r . Isopropanol (100 mis.) and 20 mis. water were used as the solvent media. Alcoholic HC1 (0.0995 N.) was used as the t i t r a n t . The calculated amount of KOH present was between 1.9 and 2.7%, which compared favorably with the theoretical value of 2.0 wt%. The procedure for the preparation of catalyst using toluene as an azeotroping agent i s s i m i l a r . The same r e l a t i v e amounts of potassium hydroxide and D4 were used and enough toluene was added to make a 50% solution. The reaction mixture was heated for about 12 hours at 95°C and then at 120°C for an additional 12 hours. In each case, the catalyst was stored under argon i n v i a l s sealed with teflon tape and placed i n a dessicator u n t i l use. To remove catalyst for use i n reactions, the v i a l was warmed s l i g h t l y , i f necessary, to reduce the v i s c o s i t y , and the desired amount of catalyst removed by pipette. Argon was then flushed through the catalyst remaining i n the v i a l , which was then resealed and returned to the dessicator.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

11. B.

SORMANI ET AL.

Anionic Polymerization of Octamethylcyclotetrasiloxane 153

E q u i l i b r a t i o n Reactions

Octamethylcyclotetrasiloxane and the α, ω aminopropyl 1,3 tetramethyldisiloxane were put into a three neck flask, f i t t e d with a reflux condenser, an argon i n l e t , and a magnetic s t i r r i n g bar. One neck of the flask was covered with a septum for the removal of samples by a syringe equipped with a stopcock. Potassium siloxanolate catalyst was pipetted into the f l a s k . The flask was then immediately f i t t e d with the argon i n l e t and heated by a s i l i c o n e o i l bath. Samples were removed at various times and put into sample v i a l s which were capped with septums. These were stored i n a refrigerator u n t i l analysis by HPLC. Some samples were analyzed immediately by c a p i l l a r y gas chromatography. C.

High Performance Liquid Chromatography

Quantitative analysis o using a Waters Model 45 employed were ODS columns, either Dupont Zorbax columns obtained from Fischer, or the Regis L i t t l e Giant. The L i t t l e Giant i s a 5 cm. long, 10 mm. i . d . column packed with 3 micron p a r t i c l e size ODSII packing. The Dupont Zorbax columns were 25 cm. long with a 10 mm. i . d . and a 10 micron p a r t i c l e size ODS packing. A d i f f e r e n t i a l refractometer and a fixed wavelength infrared detector were used. Samples were made up i n one ml. volumetric flasks i n toluene. Typical concentrations were i n the range of 10-17%. The mobile phase was composed of 35% acetone and 65% a c e t o n i t i r l e i n the case of the Dupont columns with a flow rate of 1.5 ml./min. The L i t t l e Giant column used a mobile phase of 20% acetone and 80% a c e t o n i t i r l e at a flow rate of 0.8 ml./min. The change i n mobile phase and flow rate was necessary to restore s u f f i c i e n t resolution for quantitative analysis while s t i l l maintaining fast analysis times. A l l solvents were HPLC grade solvents and were used as received with no further purification. A c a l i b r a t i o n curve was prepared for D4 by plotting peak height i n millimeters vs. micrograms injected. A 20 m i c r o l i t e r sample loop was used with the DuPont columns to ensure reproducible sample s i z e . A 35 m i c r o l i t e r sample loop was used with the short column. Larger sample volumes could be used i n this case due to a lower operating pressure. A t y p i c a l c a l i b r a t i o n curve for D4 i s shown i n Figure 1. D4 c a l i b r a t i o n curves were prepared using both the refractive index and the infrared detector. The ug of D4 corresponding to the measured D4 peak height of an e q u i l i b r a t i o n sample can be read from the c a l i b r a t i o n curve. Knowing the ul injected and the t o t a l sample weight, the D4 concentration can be determined. D.

Capillary Gas Chromatography

C a p i l l a r y gas chromatography was used to measure the amount of aminopropyl disiloxane present i n the samples. An 11 m. column with an internal diameter of 0.2 mm. coated with a dimethylsiloxane stationary phase was used. A s p l i t t e r injector was employed with a

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RING-OPENING POLYMERIZATION

s p l i t ratio of 100/1, at a temperature of 310°C. Samples were dissolved i n methylene chloride and one m i c r o l i t e r of solution injected. A flame ionization detector was employed, at a temperature of 275°C. Temperature programming was necessary to give good resolution and reasonable analysis times. The program followed was as follows: 80°C to 170°C at 5°C/min., 170°C to 225°C at 30°C/min. The c a r r i e r gas flow rate (He) was 1.7 ml/min at 80°C. Peak areas were calculated using a Perkin Elmer 3600 data station. Tetradecane (C^^) was used as an internal standard, and added from a stock solution to disiloxane or e q u i l i b r a t i o n sample solutions. Shown i n Figure 2 i s a t y p i c a l c a l i b r a t i o n curve, where the disiloxane/Ci4 area ratio i s plotted against the disiloxane/Ci4 weight r a t i o . Knowing the experimentally determined disiloxane/Ci4 area r a t i o , and the weight of added (^4 and e q u i l i b r a t i o n sample, the amount of disiloxane present i n any sample may be determined. The amount of disiloxane found i s approximately plus or minus 1%. Results and Discussion A set of control experiments was f i r s t performed, where no aminopropyldisiloxane "end blocker" was used i n the reaction. Reactions were done at 82°C, 111°C, 117°C and 140°C using s u f f i c i e n t catalyst to make 0.02 wt% KOH (0.034 m o l e / l i t e r ) . Samples were removed at convenient intervals by syringe. In the case of the reaction done at 140°C, after only 15 minutes the reaction mixture was too viscous to be removed by syringe. At 111°C i t took 120 minutes for the mixture to become too viscous for removal by syringe, while at 82°C i t took 8.5 hours to reach this point. The observed increase i n v i s c o s i t y i s expected i n the absence of endblocker and corresponds to the appearance of high molecular weight species. This presents a d i f f i c u l t y i n the k i n e t i c analysis of this data. Shown i n Figure 3 i s a plot of In [D4] vs. time for a l l four reaction temperatures. If the reaction i s f i r s t order with respect to D4 concentration, plotting In [D4] vs. time should give straight lines where the slope - -rate constant, k. However, the concentration of D4 should be monitored to at least 75% conversion to d i f f e r e n t i a t e between f i r s t and second order k i n e t i c s . In fact, in this concentration range, a second order plot - [D4] vs. [D4] time - also gives straight l i n e s . However, i t i s known that this reaction i s f i r s t order i n D4 concentration (11). In fact, a second order plot of Grubb and Osthoff's data (11) gives a plot that i s indeed linear i n the same concentration range as we have studied, but that then curves at higher concentrations. Therefore, the s i m i l a r i t y between our f i r s t and second order k i n e t i c plots i s expected i n the concentration range studied. Assuming f i r s t order k i n e t i c s , a plot of In k vs. 1/T (°K) was made (Figure 4), and the activation energy calculated to be 18.1 kcal/mole, i n good agreement with previous values calculated by other workers (9). Reactions which used either the bulk catalyst or the catalyst prepared using toluene as an azeotroping agent gave rate constants which f e l l on the same l i n e i n the Arrhenius plot, indicating that the e f f i c i e n c y of each method of catalyst preparation i s roughly the same. The next set of experiments involved the determination of the

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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Anionic Polymerization of Octamethylcyclotetrasiloxane

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RING-OPENING POLYMERIZATION

-0.6

An[D l 4

o.o

e0

50

100

150

200

250

300

350

400

450

500

time (minutes) Figure 3. Disappearance of D4 at various temperatures. • = 140°C, • = 117°C, 0 = 111°C, •= 82°C.

£n (rate constant) -6

0.0024

0.0025

0.0026 1/T

Figure 4 .

0.0027

0.0020

(°K)

Arrhenius plot f o r the reaction of D4 with potassium siloxanolate catalyst at 0.02 Wt. % KOH.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

0.0029

11.

SORMANI ET AL.

Anionic Polymerization ofOctamethylcyclotetrasiloxane 157

rate of disappearance of D4 i n the presence of disiloxane. Shown i n Figure 5 i s a plot of D4 concentration vs. time a£ 0.02 wt% KOH. In each case, the D4 concentration decreases from 75 wt% to under 10 wt% i n approximately 30 minutes. The r a t i o of D4 to disolxane i n this case should give an oligomer with = 1000. Similar results were obtained at 0.12 wt% KOH and 91 °C, 111°C, and 131 °C, shown i n Figure 6. No huge increase i n v i s c o s i t y was observed in any of these cases, i n contrast to the reactions done i n the absence of endblocker. In these reactions, the aminopropyl disiloxane i s functioning analogously to a chain transfer agent to control the molecular weight. There i s no large buildup i n v i s c o s i t y because the growing chains react with the aminopropyl disiloxane and are terminated. I t i s also interesting to note that i n the absence of disiloxane at 140°C the amount of D4 has decreased from 99 wt% to about 65 wt% at 20 minutes, which i s much more than the amount that i s remaining at the same time in the presence of disiloxane. One possible explanation o much less viscous i n th e a s i l y react with the siloxanolat species , this i s a d i f f u s i o n - c o n t r o l l e d process, the lower v i s c o s i t y has a dramatic effect on the rate of reaction of D4 with potassium siloxanolate c a t a l y s t . Lastly, the rate of reaction of the aminopropyl disiloxane was investigated. On the basis of electronegativity differences, i t would be expected that the aminopropyl disiloxane would react more slowly than D4 with the potassium siloxanolate c a t a l y s t . This was indeed found to be the case. At levels of 0.02 wt% KOH, the reaction was rather slow. However, at 0.12 wt% KOH, the reaction proceeded at convenient rates. Shown in Figure 7 i s a plot of disiloxane concentration vs. time at 0.12 wt% KOH and temperatures of 90°C, 105°C, 129°C, 140°C. For example, at a temperature of 129°C, after approximately 6.5 hours, the disiloxane concentration has decreased from 19 wt% to 2.7 wt%. (In these reactions, the i n i t i a l D4 concentration was 80 wt%. This r a t i o of D4 to disiloxane should y i e l d a 1200 oligomer.) This corresponds to an 85% decrease in the amount of disiloxane present. In contrast, at 131°C and the same catalyst l e v e l , the amount of D4 present has decreased by over 90% after only 60 minutes. Conclusions It has been found that the attack of potassium siloxanolate catalyst on octamethylcyclotetrasiloxane i s greatly accelerated in the presence of α, ω aminopropyl 1,3 tetramethyldisiloxane. The disiloxane functions analogously to a chain transfer agent and serves to prevent a large increase in v i s c o s i t y , leading to a faster rate of reaction of D4 with c a t a l y s t . The rate of reaction of aminopropyl disiloxane with potassium siloxanolate catalyst was s i g n i f i c a n t l y slower than the rate of reaction of D 4 . Temperatures above 100°C appear to most e f f i c i e n t l y incorporate the functional disiloxane at the catalyst levels studied. The studies described herein have been most useful (6,17,18,19) i n establishing reaction conditions for the synthesis of well

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RING-OPENING POLYMERIZATION

158

0.8

j

0.7

Î

time (minutes) Figure 5.

Disappearance of D4 i n the presence of aminopropyl disiloxane at 115°C (O) and 140°C (•), 0.02 Wt% KOH.

time (minutes) Figure 6.

Disappearance of D, i n the presence of aminopropyl disiloxane with 0.12 wt% KOH at temperatures of 91°C (•), 111°C (O), and 131°C (•).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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defined amino a l k y l functional oligomers, which i n turn have been employed to produce novel segmented copolymers. Acknowledgment s The authors would l i k e to thank Mr. M. Ogden for assistance with the c a p i l l a r y GC work and the Army Research Office for supporting this research under Grant DAAG-29-85-G-0019. They also thank the Exxon Educational Foundation for p a r t i a l support.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Wright, P. V., in Ring-Opening Polymerizations, K. J. Ivin and T. Saegaser, Editors, Elesevier Press (1984). Noll, W., Chemistry and Technology of Siloxanes, Academic Press, New York (1968). McGrath, J. E., Riffle Wilkes, G. L., in "Initiatio Series No. 212, F. . Bailey Jr., Editor, 1983, p. 145-172. Kantor, S. W., Grubb, W. T., Osthoff, R. C., J. Amer. Chem. Soc. 76, 5190 (1954). Riffle, J. S., Yilgor, I., Banthia, Α. Κ., Wilkes, G. L., McGrath, J. E., in Epoxy Resins II, R. S. Bauer, Editor, ACS Symposium Series No. 221 (1983). Yilgor, I., Riffle, J. S., McGrath, J. E., in "Reactive Oligomers", F. Harris, Editor, ACS Symposium Series, in press (1985). Saam, J. C., Gordon, D. J., and Lindsay, S., Macromolecules 3, 4 (1970). Bostick, Ε. E., in Block Polymers, edited by S. L. Aggarwal, Plenum Press (1970). Voronkov, M. G., Mileshkevich, V. P., Yuzhelevskii, Υ. Α., The Siloxane Bond, Consultants Bureau, New York and London (1978). Stark, F. O., Falender, J. R., Wright, A. P., in Comprehesive Organometallic Chemistry, Sir Geoffrey Wilkinson, FRS, Editor, Pergamon Press (1983). Gilbert, A. R., Kantor, S. W., J. Polym. Sci. 11, 35 (1959). Grubb, W. T., Osthoff, R. C., J. Am. Chem. Soc. 77, 1405 (1955). Cooper, G. D., J. Polym. Sci. A-1, 4, 603 (1966). Carmichael, J. B., Heffel, J., J. Phys. Chem., 69, 2213 (1964). Andrews, G., Macromolecules, 14 (5), 1603 (1981). Andrews, G., Macromolecules, 15 (6), 1580 (1982). Johnson, B. C., Ph.D Thesis, VPI and SU, June 1984, and forthcoming publications. Tran, C., Ph.D Thesis, VPI and SU, November 1984, and forthcoming publications. Yorkgitis, E., Tran, C., Eiss, N. S., Yu, Τ. Υ., Yilgor, I., Wilkes, G. L., McGrath, J. E., Siloxane Modifiers for Epoxy Resins, in "Rubber-Modified Thermoset Resins," C. K. Reiw and J. K. Gillham Editors, Adv. Chem. Series No. 208 (1984).

RECEIVED April 1, 1985

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

12 An Improved Process for є-Caprolactone-Containing Block Polymers H. L HSEIH and I. W. WANG Research and Development, Phillips Petroleum Company, Bartlesville, OK 74004 A new process, which involves the conversion of polymeric oxyl-lithium to oxyl-aluminum chain end as modified ring-opening site for lactones has proven to be ver esterifications containing styrene, butadiene, and ε-caprolactone can be prepared with well defined structure. Among i t s many attributes, poly(ε-caprolactone) (PCL) i s p a r t i c u l a r l y unique i n i t s capability to blend with different commercial polymers over a wide composition range. Incorporating PCL segment with other rubbery or glassy blocks w i l l allow us to form novel multiphase block polymers. Such specialty polymers are often used as " o i l - i n - o i l " type of emulsifiers i n polymer blends, whose mechanical properties can be improved i f better homogeneity i s achieved by the emulsifier additives 0^,2) · As to i t s other c h a r a c t e r i s t i c s , styrene-butadiene-caprolactone (S-B-CL) t r i b l o c k terpolymer with high butadiene content behaves much l i k e a thermoplastic elastomer, with raw tensile strength equal to and ozone resistance better than S-B-S type copolymer (3)· The impact-resistant resin by blending 25 parts of S-B-CL t r i b l o c k with 75 parts of s t y r e n e / a c r y l o n i t r i l e (SAN) copolymer resembles ABS type material in such properties as tensile strength, f l e x u r a l modulus, o i l resistance, and transparency (4). The melt condensation of acid and hydroxyl functional group normally requires exact stoichiometry, elevated temperature, and a long reaction cycle. Such a route would not be possible to u t i l i z e to produce block polymers from lactones and other v i n y l monomers. However, a rather f a c i l e route leading to polyester formation can be realized by the ring-opening polymerization of lactones as seen from the scheme:

0097-6156/85/0286-0161$06.00/0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

162

η n

ο

—N

( ^

H —fC-(CH ) —0}—

>

2

m

(CH ) ^ 2

m

The anionic ring-opening mechanism which involves acyl-oxygen cleavage with subsquent propagation through an alkoxide anion raises the p o s s i b i l i t y of block polymerizing lactone molecules with other v i n y l monomers. For example, the a l k y l l i t h i u m - i n i t i a t e d polystyryl and polydienyl anions, or their corresponding oxyl-lithium anions, have been employed as c r o s s - i n i t i a t o r for ε-caprolactone block polymerization (3,5)· I d e a l i s t i c a l l y , well defined block polymers of ε-caprolactone, styrene, and butadiene can be made through such a method. However, i n the ring-openin anionic conditions i t i s d i f f i c u l t to eliminate the unzipping and ester scrambling interferences, which are two major side reactions concurrent with the polyester formation (5)· The depolymerization due to unzipping, or back-biting, phenomenon can be visualized through the intramolecular version of ester interchange: 0

0

0

0

ORIGINAL Δ J PROCESS

0 Δ

70°C

if V



-O

^ o - o

95 CONVERSION

1

1

85 80

B-CL (70--30 WT% ) DIBLOCK 75

V

1

0

.5 1.0 1.5 2.0

70 3

4

5

6

TIME FOR CL AT 4th STEP, HR. Figure 3· Comparison between o r i g i n a l and improved process f o r B-Cl diblock copolymerization.

W dl/g 10.0

4.0 3.Oh 2.0

Δ Δ Δ

1.0b

*0«

I I III III,

0.1 10"

Ο

ο

I lilllUI III 10

io~

MTJ Figure 4. Molecular weight c o r r e l a t i o n with i n t r i n s i c v i s c o s i t y i n toluene.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

At 50°C. Alcohol coagulation. IR analysis. GPC/universal c a l i b r a t i o n curve. Rheovibron measurement at 11 Hz.

100

100

64-3

8

99

64-2

64-4

98

64-1

200/147 143/110 100/78

1.36 1.30 1.27

56

56

δ z

Ν

m 2

Ο

Ζ Ζ ο "Ό

m

283/216 1.31

2

ζ ο ό

-86 69/53

1.29

0

30

100

4

16-4

-86 64/51

1.26

0

30

99

3

16-2

56 -86 92/65

1.41

0

29

13-8

57 -86

101/74

99

13-5

Transition Temp., °C Tm

3

3d

MnxlO"

Mwxl0"

Tg

4

MWD

1.37

C

0

b

30

6

Sample

100

CL Block Pzn Time , hr

Wt.% Acetone Extractable

% Final Conv.

B-CL (70-30 wt%) Diblock Copolymers

Wt.% CL found i n B-CL

a

Table I I .

12.

HSEIH A N D WANG

e-Caprolactone-Containing Block Polymers

Ν ιΛ CO CO νΟ Η Ν Csl ι—I ι—I

o o v o c o s r Ο O CM O CO Π Ν H H H

tn νο

m σι m «ί

Ν Η

oo

σ\ιη

m

CM Ο ι—I ι—I

CO ι—I

ο

u

ω

SI

Η

Ν Ν

»ί

Ν

ΙΛ Η Η Η

Ν

>ί vo σ» Μ

Τ3

C (0

CO

C

g.

CO CO

ιΗ Ο

α ο υ

00 νΟ

ι-·

ON

Ν



CO

ON Ο CM

S

CM Ν

1—4

Ο

Q) C

HI

m ^-ι 2 and (CH3>3C-CH2—OCH2) and some trimers. We can conclude that CH i n i t i a t i o n by addition onto the t e r t i a r y b u t y l cation i s p r a c t i c a l l y non existent since i t could not be detected, but that i n i t i a t i o n took place by proton elimination producing isobutene; this l a t t e r , i n an a c i d i c medium, gives r i s e to some dimers and trimers terminated by a double bond after elimination (16). We have also used 2-iodopropane and 3-iodopentane as models for polybutadiene carrying some secondary iodide obtained after reacting HI onto polybutadiene under controlled conditions to avoid c y c l i z a t i o n . The results are presented on F i g . 2. Under our conditions 2-iodopropane i s a f a s t , quantitative i n i t i a t o r proceding by addition (16) through proton elimination i s t h e o r e t i c a l l y possible; 3-iodopropane, a better model for the polymer shows a d r a s t i c a l l y d i f f e r e n t behavior: only 25% of the i n i t i a t o r proceeds by addition, the rest i . e . 75% proceeds by elimination and indeed we determined the presence i n the solution of various compounds such as 1-pentene and 2-pentene, and several of their dimers and trimers 3

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

14.

Cationic Heterocyclic Polymerization

FRANTA AND REIBEL

lOOk-O

187

Ο—O-

50

-

10 _L

100

50 time (minutes) Figure 2.

E f f i c i e n c y of d i f f e r e n t secondary iodides i n the poly­ merization of THF: 2-iodopropane(o), 3-iodopentane(Q) , hydroiodated polybutadiene (...-CH -CH=CH-(CH )2-CHI(CH )3-CH=CH) (Δ); |M| = 12.3 M, 1.5 χ 10 M

„ , Polymer

(2)

Art"!" χ" HX Formation

Attack of

The observation that only a very small portion of the polymer chains which were produced using diaryliodonium s a l t s contain end groups which are derived from i n i t i a t o r fragments' suggests that the process shown i n Equation 3 i n which Brrfnsted acids are formed i s dominant. The rate of photolysis of diaryliodonium s a l t s and hence the number of i n i t i a t i n g species generated per given i r r a d i a t i o n time and l i g h t intensity i s related to the structure of the cation which i s the l i g h t absorbing species. A bathochromic s h i f t i n the absorp­ tion bands i s observed when electron releasing substituents are introduced into the ortho and para positions of the aromatic rings. Conversely, the absorption bands are s h i f t e d to shorter wavelengths when electron withdrawing substituents are placed at these positions Using these general guidelines, i t i s possible to design p h o t o i n i t i ators whose absorption c h a r a c t e r i s t i c s l i e i n v i r t u a l l y any desired portion of the u l t r a v i o l e t spectrum. Although the anion of a d i ­ aryliodonium s a l t plays no r o l e i n i t s photochemistry, i t i s the dominant factor i n the subsequent polymer chemistry since i t deter­ mines the r e a c t i v i t y of both the i n i t i a t i n g and propagating species as well as c o n t r o l l i n g which termination processes occur. Among the most useful diaryliodonium s a l t p h o t o i n i t i a t o r s are those which bear the very weakly n u c l e o p h i l i c anions such as BF ", A~» ^ A~» * p f

S F

A

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

A

N

C

15.

Thermally or Photochemically Induced Cationic Polymerization

CRIVELLO

SbFg . These p h o t o i n i t i a t o r s are capable of polymerizing almost every known type of c a t i o n i c a l l y polymerizable monomer. Due to the very weakly n u c l e o p h i l i c character of these anions, termination i s very slow i f not absent and i n c e r t a i n cases such as i n the polymeri­ zation of tetrahydrofuran, l i v i n g cationic polymerizations are ob­ served with such i n i t i a t o r s . The photolysis of diaryliodonium s a l t s can be carried out i n the long wavelength UV and i n the v i s i b l e region of the spectrum although they do not absorb at these wavelengths provided that photosensitizers are employed(4,5). Diarylketones, condensed r i n g aromatic hydrocarbons and phenothiazines are excellent photosensi­ t i z e r s f o r use i n the UV, while the acridinium and benzothiazolium dyes, acridine orange and setoflavin-T are a c t i v e photosensitizers for the short wavelength v i s i b l e region. A mechanism involving electron transfer has been implicated i n photosensitization and i s depicted i n Equations 4-7.

P*

+

Ar I

[P-.-Ar I

+

X"

2

+

>

X~]*

2

> P"f"x"

+ η M

[P---Ar I

P

X

+

+

X"]*

Ar I-

(5) (6)

-

* >

-{M>-

(7)

η

The key feature of t h i s mechanism i s that the excited photosensitizer, Ρ , i s oxidized by the diaryliodonium s a l t which i s correspond­ ingly reduced. This mechanism i s substantiated by f i r s t , the d i r e c t experimental observation of photosensitizer c a t i o n - r a d i c a l species by UV and ESR spectroscopy(6) and second, by a d i r e c t c o r r e l a t i o n between the a c t i v i t y of a photosensitizer and the reduction p o t e n t i a l of i t s excited state r e l a t i v e to the diaryliodonium salt(3>,5). It i s interesting to note that the c a t i o n - r a d i c a l , PÎ, derived from the photosensitizer rather than from the p h o t o i n i t i a t o r i s responsible for i n i t i a t i n g polymerization i n t h i s instance. Thermally I n i t i a t e d Cationic Polymerization I n i t i a t o r s Activated by Elevated Temperatures. Although, as men­ tioned e a r l i e r , diaryliodonium s a l t s possess considerable thermal s t a b i l i t y and, therefore, cannot be used d i r e c t l y i n thermally activated polymerizations, we sought to f i n d some way i n which the thermal latency of these i n i t i a t o r s could be broken. This appeared to be possible on the basis of a recent general reaction discovered i n our laboratory(7,8). Diaryliodonium s a l t s undergo f a c i l e reac­ tion with nucleophiles whereby the nucleophile i s arylated as de­ picted i n Equation 8. Ar I ^

+

X"

+

Nu

Cu(II) >

+

ArNu x"

+

Arl

(8)

A

This reaction proceeds smoothly at temperatures from 100-125°C i n the presence of a c a t a l y t i c amount of a copper compound to give high y i e l d s of the arylated product. Furthermore, as shown i n Scheme 1,

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

197

198

RING-OPENING POLYMERIZATION

the reaction i s applicable to a wide variety of substrates. Even compounds as poorly nucleophilic as diphenylsulfide are quantita­ t i v e l y arylated i n one hour at 125°C. Scheme 1

Realizing that c a t i o n i c a l l y polymerizable monomers are, by d e f i n i ­ t i o n , nucleophiles, i t appeared that i t might be possible to i n i t i ­ ate cationic polymerization using the same a r y l a t i o n reaction. In­ deed, when c a t i o n i c a l l y polymerizable monomers were heated at tem­ peratures i n excess of 80°C i n the presence of diaryliodonium s a l t s containing a trace of cupric benzoate as a catalyst, spontaneous polymerization was observed(9). The polymerization i s completely general with respect to the types of monomers which can be used. Among those representative monomers which have been thermally polymerized using t h i s new catalyst system include: cyclohexene1,2-oxide, s-trioxane, 2-chloroethyl v i n y l ether, ε-caprolactone, α-methylstyrene, and tetrahydrofuran. Figure 1 gives the r e l a t i o n ­ ship between the reaction time and the conversion of monomer to polymer i n the polymerization of ε-caprolactone. In the polymeriza­ t i o n of t h i s p a r t i c u l a r monomer, an i n h i b i t i o n period can be c l e a r l y seen. In Figure 2 i s shown the effect of the concentration of the diaryliodonium s a l t on the rate of conversion of phenyl g l y c i d y l ether to polymer. As the diaryliodonium s a l t i s increased, the rate of polymerization i s also correspondingly increased. A l l d i ­ aryliodonium s a l t s examined behaved s i m i l a r l y , provided they pos­ sessed the weakly nucleophilic anions mentioned above. In contrast to the marked influence of the diaryliodonium s a l t concentration on the polymerization rates, the effect of the con­ centration of the copper compound was found to be c a t a l y t i c . In general, 10 mole % with respect to the diaryliodonium s a l t was found to be s u f f i c i e n t . Although many d i f f e r e n t t r a n s i t i o n and nont r a n s i t i o n metals i n various oxidation states were examined, only

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

15.

CRIVELLO

Thermally or Photochemically Induced Cationic Polymerization 199

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

Figure 2.

E f f e c t of the concentration of ( C ^ I ^ ^ I AsF^ on the polymerization of phenyl g l y c i d y l ether at 85°C for 30 min catalyzed by 1.6 χ 10"^ mol Cu(II) benzoate.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

15.

Thermally or Photochemically Induced Cationic Polymerization

CRIVELLO

copper compounds were catalysts for the polymerization reaction. V i r t u a l l y any copper compound can be used as a c a t a l y s t ; however, those compounds such as cupric stéarate and cupric benzoate which have appreciable s o l u b i l i t y i n organic media were most u s e f u l . A number of experiments designed to elucidate the nature of the c a t a l y s i s by copper were carried out. I t was observed that when Cu(II) compounds were combined with diaryliodonium s a l t s i n com­ p l e t e l y unreactive solvents such as chlorobenzene, there was no reaction even at elevated temperatures. In contrast, diaryliodonium s a l t s reacted rapidly and q u a n t i t a t i v e l y even at 25°C i n various solvents i n the presence of c a t a l y t i c amounts of a Cu(l) compound. Analysis of the products of t h i s l a t t e r reaction shown i n Equation 9

6%

tr.

are consistent with the p r i o r suggestion that a r y l a t i o n of a nucleop h i l e , i n t h i s case the solvent methanol, takes place during the reaction. Given the observation that only Cu(I) species are active as c a t a l y s t s i n the above a r y l a t i o n reaction, i t appeared that when Cu(II) compounds are employed i n these i n i t i a t o r systems, a reduction must occur to generate the c a t a l y t i c a l l y active Cu(I) oxidation state. In l i g h t of the above observations, the mechanism shown i n Equations 10-13 has been proposed for the thermal i n i t i a t i o n by d i ­ aryliodonium s a l t s i n the presence of Cu(II) c a t a l y s t s ( 9 ) . Red-H Ar I 2

+

X~

+

Cu(II)L

+

Cu(I)L

[ArCu(III)LX] +

Ar-M X"

»

2

Red

+

Cu(I)L

> [ArCu(III)LX] +

+

M

>

Ar-M X~

+

+

ηM

>

Ar-(M)-M χ" η

+ +

HL Arl

Cu(I)L

+

(10) (11) (12) (13)

The reaction of the Cu(I) species with the diaryliodonium s a l t re­ sults i n the formation of a proposed organometallic intermediate, [ArCu(III)LX], whose structure has not been f u l l y elucidated due to i t s l a b i l i t y . This intermediate undergoes as i t s primary reaction, an e l e c t r o p h i l i c attack on the monomer, M, to i n i t i a t e cationic polymerization. The above mechanism predicts and i t has been con­ firmed that only trace amounts of reducing agents are required to convert a c a t a l y t i c quantity of Cu(II) compound to i t s lower valence state. Once the Cu(I) i s formed, i t i s continually recycled between Equations 11 and 12 u n t i l a l l the diaryliodonium s a l t has been con­ sumed. Another consequence of t h i s mechanism i s that polymers pre­ pared using these catalysts should possess aromatic end groups which

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

201

202

RING-OPENING POLYMERIZATION

originate from the diaryliodonium s a l t . Indeed, bands due to the presence of aromatic end groups can be observed i n the UV spectra of polycyclohexene oxide and poly-e-caprolactone prepared using these i n i t i a t o r s . Additional work with model compounds shown i n Equations 14 and 15 has v e r i f i e d that the chief mode of i n i t i a t i o n involves a r y l a t i o n of the monomer.

(14)

(15) The nature of the reducing agent, Red-Η, has been the subject of a considerable amount of research. In most cases, and especially when oxygen containing heterocyclic monomers are used, the major r e ­ ducing agents are alcohols which are present i n these monomers as impurities or as a result of hydrolysis. Further, Cu(II) compounds are known to oxidize a l i p h a t i c alcohols at elevated temperatures(10). L a s t l y , the addition of small amounts of such alcohols results i n a reduction i n the i n h i b i t i o n period at the start of the polymeriza­ t i o n and increases the o v e r a l l rate. I n i t i a t o r s Active at Room Temperature. The a b i l i t y of Cu(I) com­ pounds to catalyze the quantitative reduction of diaryliodonium s a l t s has l e d to the design of a number of novel i n i t i a t o r systems which can be used at low temperatures. The most simple of these systems consists of adding a Cu(I) compound d i r e c t l y to an appro­ p r i a t e monomer containing a diaryliodonium s a l t . Spontaneous poly­ merization i s observed on mixing. A l t e r n a t i v e l y , the Cu(I) species can be generated by an i n - s i t u reduction of the corresponding Cu(II) compound. This can be accomplished by the addition of e a s i l y o x i ­ dized alcohols such as benzoin or ascorbic acid, which reduce Cu(II) compounds at room temperature. Again, when these reducing agents are added to reactive monomers containing diaryliodonium s a l t s and Cu(II) c a t a l y s t s , spontaneous cationic polymerization occurs at 25°C on mixing(11,12). Another very useful class of reducing agents which can be used are Sn(II) carboxylates(13)· In the presence of a Cu(II) c a t a l y s t , Sn(II)-2-ethylhexanoate quantitatively catalyzes the decomposition of diaryliodonium s a l t s . Model reactions have shown that the i n i ­ t i a l step i n t h i s reaction i s the f a c i l e reduction of Cu(II) to Cu(I) by the Sn(II) compound as depicted i n Equation 16. 2Cu(II)L

2

+

Sn(II) L 2

f 2

> 2 Cu(I)L +

Sn(IV)L' L

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

2

2

(16)

15.

CRIVELLO

Thermally or Photochemically Induced Cationic Polymerization 203

Free Radical I n i t i a t o r s as Reducing Agents for Diaryliodonium S a l t s . A f i n a l method by which diaryliodonium s a l t s can be used as thermal i n i t i a t o r s of c a t i o n i c polymerization has recently been reported by Ledwith and h i s coworkers(14,15) and i s shown i n Equations 17-19. R-R R- + A r I 2

+

— > 2RX"

Ar- + THF

> R

(17) +

X" +

> ArH + THF-

Arl

+

Ar-

etc.

(18) (19)

\

Free r a d i c a l s produced by the thermolysis of t y p i c a l r a d i c a l i n i t i a ­ tors as AIBN, benzopinacole and phenylazotriphenylmethane reduce the diaryliodonium s a l t generating a r y l r a d i c a l s and solvent derived r a d i c a l s which i n a chain reaction induce the decomposition of more diaryliodonium s a l t . Through the s e l e c t i o n of p a r t i c u l a r r a d i c a l i n i t i a t o r s with s p e c i f i just the i n i t i a t i o n temperatur considerable l a t i t u d e . Conclusions Diaryliodonium s a l t s are a novel and highly v e r s a t i l e class of i n i t i a t o r s for c a t i o n i c polymerization. These compounds are e f f i ­ cient p h o t o i n i t i a t o r s of c a t i o n i c polymerization whose structure may be readily modified to achieve a wide degree of photosensitivity and r e a c t i v i t y . While these compounds are unique i n that they do not thermally i n i t i a t e polymerization even at elevated temperatures, they can be converted to excellent thermal i n i t i a t o r s simply through the addition of c a t a l y t i c quantities of a copper(II) compound. The further discovery that the addition of reducing agents markedly accelerates the i n i t i a t i o n and lowers the i n i t i a t i o n temperature allowed the design of systems which i n i t i a t e polymerization spon­ taneously at 25°C on mixing or at any desired temperature. T y p i c a l reducing agents which have been explored are: ascorbic a c i d , benzoin, Sn(II) carboxylates i n combination with Cu(II) compounds and common free r a d i c a l progenitors. Literature Cited 1. Crivello, J. V.; Lam, J. H. W. Macromolecules 1977, 10, 1307. 2. Pappas, S. P.; Gatechair, L. R. Proc. Soc. Photogr. Sci & Eng. 1982, 46. 3. Timpe, H.-J.; et al Z. Chem. 1983, 3, 102. 4. Crivello, J. V.; Lam, J. H. W. J. Polym. Sci., Polym. Chem. Ed. 1978, 16, 2441. 5. Pappas, S. P.; Jilek, J. H. Photogr. Sci. Eng. 1979, 23, 140. 6. Crivello, J. V.; Lee, J. L. unpublished results. 7. Crivello, J. V.; Lam, J. H. W. J. Org. Chem. 1978, 43, 3055. 8. Crivello, J. V.; Lam, J. H. W. Synth. Comm. 1979, 9, 151. 9. Crivello, J. V.; Lockhart, T. P.; Lee, J. L. J. Polym. Sci., Polym. Chem. Ed. 1983, 21, 97. 10. Clarke, H. T.; Dreger, Ε. E. Org. Syn., Coll. Vol. 1 1941, 87. 11. Crivello, J. V.; Lee, J. L. J. Polym. Sci.,Polym. Chem. Ed. 1981, 19, 539.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

204

12. Crivello, J. V.; Lee, J. L. J. Polym. Sci., Polym. Chem. Ed. 1983, 21 1097. 13. Crivello, J. V.; Lee, J. L. Makromol. Chem. 1983, 184, 463. 14. Abdul-Rasoul, F. A. M.; Ledwith, Α.; Yagci, Y. Polymer 1978, 19, 1219. 15. Abdul-Rasoul, F. A. M.; Ledwith, Α.; Yagci, Y. Polymer Bull. 1978, 1, 1. RECEIVED September 14, 1984

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

16 Polymerization of Substituted Oxiranes, Epoxy Aldehydes, and Derived Oxacyclic Monomers Z. J. JEDLIŃSKI, M . BERO, J . K A S P E R C Z Y K , and M . K O W A L C Z U K Institute of Polymer Chemistry, Polish Academy of Sciences, Curie-Sklodowskiej 34, 41-800 Zabrze, Poland

This paperisa review of studies on the ring-opening polymerization of cyclic ethers, e.g., styrene oxide, phenyl glycidyl ethers, epoxy aldehydes and derived oxacyclic monomers. Model reactions involving ring­ -openingprocesses occurring in those compounds have also been discussed.

Many papers have been p u b l i s h e d concerning the s t r u c t u r e o f the a c t i v e centers i n anionic and c a t i o n i c ring-opening polymerization reactions of o x a c y c l i c monomers. Recently, a t t e n t i o n has been paid i n our l a b o r a t o r y t o the i n f l u e n c e of the s t r u c t u r e of complex carbonium s a l t i n i t i a t o r s , e s p e c i a l l y of the dioxolanylium s a l t s used f o r i n i t i a t i n g t h e c a t i o n i c p o l y m e r i z a t i o n r e a c t i o n s o f t r i o x a n e , t e t r a h y d r o f u r a n and d i o x o l a n e , on the course o f t h e polymerization (1_). In the present report some examples of the influence of monomer structure, e s p e c i a l l y of s t e r i c hindrance and e l e c t r o n i c e f f e c t s , on the mechanism o f p o l y m e r i z a t i o n and on the nature of the a c t i v e centers formed i n the anionic p o l y m e r i z a t i o n o f c e r t a i n o x a c y c l i c monomers are discussed. Polymerization of Styrene Oxide In t h e p o l y m e r i z a t i o n of s u b s t i t u t e d o x i r a n e s , t h e d i r e c t i o n o f opening o f t h e epoxy r i n g i s o f great importance because i t 0097-6156/85/0286-O205$06.00/0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

206

RING-OPENING POLYMERIZATION

determines both the k i n d of a c t i v e c e n t e r s present i n t h e polymerization reaction and the molecular structure and properties of the p o l y e t h e r s formed. I n t h i s regard, three d i f f e r e n t epoxyr i n g - o p e n i n g r o u t e s a r e p o s s i b l e : (1) β-ring opening; t h a t i s , opening of the O-CH2 bond; (2) α-ring opening, t h a t i s , opening o f the 0-CHR bond; and (3) combined a- and β-ring opening, as shown below:

POLYMER:

SCISSION: RRR...

..sss...

isotactic or atactic

\

CH — CHn ** Ο (R) • (S)

1. inversion 2. retention

or

)

isotactic SSS. .1 isotactic

.RRR.. + .

SSRSRSS. 3. racemization. .SSRSRSS.

atactic atactic

As a r e s u l t o f the β-ring opening, the c o n f i g u r a t i o n o f t h e asymmetric carbon atom remains unchanged. However, the α-ring opening may take place with e i t h e r an i n v e r s i o n or retention of the configuration, depending on reaction conditions. C e r t a i n g e n e r a l r u l e s determining the conditions f o r a- or βring-opening processes have been established from the i n v e s t i g a t i o n s of C. C. P r i c e (2^) and E. Vandenberg (3) and the g e n e r a l view i s t h a t i n the a n i o n i c p o l y m e r i z a t i o n o f epoxides, t h e r i n g opening occurs at the β p o s i t i o n , while f o r c a t i o n i c i n i t i a t o r s , both a- and β-ring opening take place simultaneously with the formation of both c y c l i c oligomers and l i n e a r oligomers containing i r r e g u l a r head-tohead and regular h e a d - t o - t a i l sequences. This l a t t e r t y p i c a l course f o r these p o l y m e r i z a t i o n r e a c t i o n s has been found t o occur i n the case of phenyl g l y c i d y l ethers polymerized by Lewis acids, and a l s o quite s u r p r i s i n g l y , polymerized by aluminum alkoxides (4). There a r e , however, numerous e x c e p t i o n s t o those r u l e s . F o r i n s t a n c e , Tsuruta showed t h a t t - b u t y l o x i r a n e p o l y m e r i z e d i n t h e presence of BF3 gave a polymer with regular h e a d - t o - t a i l sequences, by an almost e x c l u s i v e l y β-ring-opening process (5). Such a course f o r the polymerization reaction r e s u l t s from the considerable s t e r i c hindrance provided by the bulky t - b u t y l substituent. In recent studies of styrene oxide polymerization reactions we found the phenyl substituent t o have a s i g n i f i c a n t i n f l u e n c e on the course of the polymerization process, too. In our p a r t i c u l a r case, however, the influence i s due not only to s t e r i c f a c t o r s , but a l s o t o the i n d u c t i v e e f f e c t s o f t h e phenyl r i n g , which i n f l u e n c e s d i r e c t l y the course of the oxirane ring-opening reaction. 9

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

16.

Polymerization of Cyclic Ethers: Review

JEDLINSKI ET AL.

207

Anionic Polymerization by Sodium Methoxide Catalyst The d i r e c t i o n of the ring opening i n the anionic polymerization of styrene oxide was determined both by analyzing the products of model reactions i n v o l v i n g the addition of a l c o h o l s to the monomer and by s t r u c t u r a l s t u d i e s of the polymers and o l i g o m e r s obtained. The model addition reactions of a l c o h o l s to styrene oxide, catalyzed by the sodium alkoxide, showed that the oxirane ring opens i r r e g u l a r l y , both i n the a- and β-positions according to the a l c o h o l i n v o l v e d . The r e s u l t s of t h i s study are c o l l e c t e d i n T a b l e I. In the p o l y m e r i z a t i o n r e a c t i o n , polymer with a number average molecular weight of a p p r o x i m a t e l y 3,000 was obtained with CR^ONa i n i t i a t o r c o n c e n t r a t i o n of about 2 mole %. T h i s polymer was found to be a t a c t i c with a regular head-to-tail chain sequence as determined by i t s C NMR spectra i n Figure 1. With a high c o n c e n t r a t i o n of t h i s i n i t i a t o r (25 mole % ) , the formation of low molecula c o n t a i n e d the l i n e a r dimer weight, and higher l i n e a r oligomers, E, i n about 70% by weight: 1 3

A

C

ι

E

ι

CKpCH^CHOH

957.

ι

CH^OCH^CHOCH^CHOH 95,3*

The dimer C i s formed by an i n i t i a l α-ring-opening r e a c t i o n followed by a β-ring-opening one, while the dimer D i s formed by a double β-ring-opening process. The reaction mixture was a l s o found to c o n t a i n about 1% by weight of the monomeric a l c o h o l s , A and B, formed by both a- and β-ring-opening processes. From these findings, and from r e s u l t s of the model reactions i n T a b l e I, which showed t h a t the b u l k i e r the s u b s t i t u e n t i n the a l c o h o l , the greater the p a r t i c i p a t i o n of the β-ring opening, i t i s p o s s i b l e to propose the f o l l o w i n g mechanism of i n i t i a t i o n and propagation f o r the p o l y m e r i z a t i o n of s t y r e n e oxide by the sodium methoxide:

0

^7 / R

0

CH-CH - O - C H j - C H - O *

Γ°

0

0 ~ C H2 - C H - 0

I

0, R-CH.-CH-O 1

I

0

0

v β

R-CH-CH-0-CH-CH-0*

ι

0

ι 0

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

208

RING-OPENING POLYMERIZATION

ί Ί Γ «•CH -CM Of

9

h

4CH-CMJO^

m r I I

Figure 1.

13c-NMR 20 MHz s p e c t r a of p o l y ( s t y r e n e oxide) o b t a i n e d from the following polymerization reactions: (a) R,S - styrene oxide i n i t i a t e d with CR^ONa as i n i t i a t o r (b) R,S - styrene oxide catalyzed with Al(0iPr)3 as i n i t i a t o r (c) R(+) - styrene oxide i n i t i a t e d with Of^ONa as i n i t i a t o r (d) R(+) - styrene oxide catalyzed with Al(0iPr)3 as i n i t i a t o r

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

16.

JEDLINSKI ET AL.

Polymerization of Cyclic Ethers: Review

209

According to these experimental r e s u l t s , the proposed reaction mechanism f o r the formation of p o l y ( s t y r e n e oxide) with a r e g u l a r chain structure by anionic polymerization i n v o l v e s the oxirane ring opening e x c l u s i v e l y at the β position. However, two kinds of a c t i v e c e n t e r s , A and Β i n the r e a c t i o n s above, occur i n the i n i t i a t i o n step. The a c t i v e center A, formed by α-ring opening, adds to a monomer m o l e c u l e i n the next step, but i n the second step the oxirane ring i s opened at the β position. Polymerization by Aluminum Alkoxides Catalyst The polymerization of monosubstituted oxiranes catalyzed by aluminum a l k o x i d e s i s of p a r t i c u l a r i n t e r e s t from the p o i n t of view of the s t e r e o c h e m i s t r y of the ring-opening r e a c t i o n . The oxiranes which have been s t u d i e d to date, i n c l u d i n g propylene oxide and phenyl g l y c i d y l ethers, were found to polymerize with aluminum alkoxides to y i e l d polymers with an head-to-head and t a i l - t o - t a i were formed as a r e s u l t of the oxirane r i n g opening at both the α and β positions, and they had the same chain microstructure as those obtained by the p o l y m e r i z a t i o n r e a c t i o n s i n i t i a t e d by standard c a t i o n i c c a t a l y s t s , such as Lewis acids. The polymerization of styrene oxide by such cationic i n i t i a t o r s as BF3H2O, SnCl4, FeCl3, e t c . does not l e a d to the formation of polymers with high m o l e c u l a r mass, but o n l y low m o l e c u l a r mass oligomers, both l i n e a r and c y c l i c , are formed. On the other hand, p o l y m e r i z a t i o n r e a c t i o n s c a r r i e d out with aluminum i s o p r o p o x i d e r e s u l t i n the formation of both an oligomeric f r a c t i o n and a polymer of higher molecular mass (FT 2500). The r e s u l t s of spectroscopic s t u d i e s i n d i c a t e t h a t the polymer i s both r e g u l a r and a t a c t i c , a c c o r d i n g to the spectrum i n F i g u r e l b . The model r e a c t i o n s of a d d i t i o n of a l c o h o l s to the styrene oxide i n the presence of s u i t a b l e aluminum a l k o x i d e s showed that the oxirane r i n g opens almost e x c l u s i v e l y at the α p o s i t i o n as seen by the data i n T a b l e II. I t was considered of i n t e r e s t , t h e r e f o r e , to i n v e s t i g a t e the mechanism of p o l y m e r i z a t i o n and the k i n d of a c t i v e c e n t e r s which g i v e r i s e to the formation of the r e g u l a r , a t a c t i c p o l y ( s t y r e n e oxide). O p t i c a l l y a c t i v e monomer was prepared and polymerized for t h i s purpose. The polymerization of R(+)-styrene oxide by Al(0iPr)3 lead to the formation of i s o t a c t i c poly(styrene oxide), as indicated i n F i g u r e Id, w i t h a p o s i t i v e o p t i c a l r o t a t i o n , w h i l e the p o l y m e r i z a t i o n of R(+)-styrene oxide by CH3UNa gave an i s o t a c t i c polymer, Figure l c , with a negative rotation. As indicated e a r l i e r , n

i n the a n i o n i c p o l y m e r i z a t i o n by sodium methoxide, p o l y ( s t y r e n e oxide) i s formed e x c l u s i v e l y by a β-ring-opening reaction i n which the c e n t e r of asymmetry and the c o n f i g u r a t i o n of the asymmetric carbon atom remain unchanged. Therefore, the p o l y m e r i z a t i o n of R(+)-styrene oxide by CH3ÛNa r e s u l t e d i n the formation of an i s o t a c t i c R(-)-polymer, while the dextrarotatory poly(styrene oxide) obtained with A l ( 0 i P r ) 3 had an S c o n f i g u r a t i o n of the asymmetric carbon atoms. Consequently the α p o s i t i o n of the oxirane r i n g opened and an inversion of configuration of the center of asymmetry took p l a c e f o r the l a t t e r c a t a l y s t , w h i l e β-ring opening with retention occurred for the former i n i t i a t o r , as shown below:

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

210

RING-OPENING POLYMERIZATION

Table I. Products obtained by the addition of alcohols to styrene oxide under the influence of sodium alkoxides

Products Initiator

Alcohol

CH 0Na

CH 0H

i-PrONa

i-PrO

3

3

t-BuONa

t-BuOH

Table I I .

β-Opening

α-Opening

2-methoxy-2-2 phenylethanol 35 mol %

2-methoxy-l-l phenylethanol 65 mol %

2-phenylethano 12 mol %

1-phenylethano 88 mol %

2-t-butoxy-2phenylethanol 6 mol %

2-t-butoxy-lphenylethanol 94 mol %

Products obtained by the addition of alcohols to styrene oxide under the influence of aluminum alkoxides

Products Initiator

Ak*0Et)

3

Alcohol

α-Opening

EtOH

2-ethoxy-2-2 phenylethanol 100%

β-Opening

-

Al(0iPr)

3

i-PrOH

2-isopropoxy-2phenylethanol 95 mol %

2-isopropoxy-lphenylethanol 5 mol %

Al(0tBu)

3

t-BuOH

2-t-butoxy-2phenylethanol 91 mol %

2-t-butoxy-lphenylethanol 9 mol %

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

16.

JEDLINSKI ETAL.

211

Polymerization of Cyclic Ethers: Review

0

I

-f-O-CH-CH^ poly R (-)

0 \

CH-CH

V

[m]

s7e

-133,2

e

2

poly-PEMA^N'^^N^I

poly-ΡΕΜΑ'—N, I Ph

^11

TBA

poly-PEMA-poly-TBA

Consequently, the ΡΕΜΑ aziridinium ion and the TBA aziridinium ion must have similar r e a c t i v i t i e s towards the TBA monomer. This i s a strong evidence that the main reason for the much slower polymerization of ΡΕΜΑ compared with TBA must be the lower r e a c t i v i t y of the ΡΕΜΑ monomer rather than a lower r e a c t i v i t y of the ΡΕΜΑ aziridinium ion. The v a l i d i t y of this statement i s now further investigated by copolymerization experiments. Copolymerization of N-alkylaziridines with β-propiolactone. 3 propiolactone (PL) reacts with t e r t i a r y amines to form the corresponding zwitterion (7^). I f an N-substituted a z i r i d i n e i s used, a zwitterion containing an aziridinium ion and a carboxylate ion i s formed. This zwitterion can i n i t i a t e a cationic polymerization of the a z i r i d i n e or an anionic polymerization of the lactone or undergo a coupling reaction with another (monomeric or polymeric) zwitterion.

T B A ^ / ^

^

\

\

N S

JPL

N^coo-\.coo

\ coupling s

e

X

-\-

X

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

226

RING-OPENING POLYMERIZATION

υV

Elution volume

»-

Figure 3 . GPC a n a l y s i s o f poly-TBA-poly ΡΕΜΑ

block-

copolymer (A) and o f the poly-TBA used as the macromolecular

initiator(B).

E l u t i o n volume

-

F i g u r e 4 . GPC a n a l y s i s o f poly-PEMA-poly TBA blockcopolymer (A) and o f the poly-ΡΕΜΑ used as the macromolecular i n i t i a t o r (B).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

17.

GOETHALS ET AL.

Polymerization of Ν-A Ikylaziridines

227

The last reaction i s another example of a spontaneous "alternating" copolymerization between an e l e c t r o p h i l i c and a nu­ c l e o p h i l i c monomer as described by Saegusa (8). The structure of the resulting polymer i s determined by the rate constants of the d i f f e r e n t reactions and by the concentration of the two monomers. This reaction has been investigated with the monomer pair PL-TBA, i n d i f f e r e n t solvents at 50°C. The polymers formed at the beginning of the reaction contain a considerable excess of amino units which proves that the cationic a z i r i d i n e propagation i s more important than the anionic lactone propagation under the reaction conditions used. A special feature of this polymerization, however, i s that large amounts (up to 50%) of c y c l i c oligomers are formed, which i s obviously due to an intramolecular coupling reaction between a carboxylate ion and an aziridinium ion of oligomeric products. This i s c l e a r l y demonstrated by the GPC analysis of the reaction mixture as shown i n Figure 5. The oligomers coul coupling with the mass-spectrometer allows one to determine their structures (Figure 6). Table I I gives a survey of the structure and the r e l a t i v e abundance of c y c l i c oligomers formed i n the copolymerization of TBA and PL. The masses a l l correspond to the general formula ^ L ^ with η • 2, 3 or 4 and m - 1 or 2 (A = amine u n i t , L = lactone u n i t ) . Since i t i s unlikely that zwitterionic species would be v o l a t i l e , i t must be accepted that these oligomers are c y c l i c .

Table I I . Structure and r e l a t i v e abundance of c y c l i c oligomers formed i n the spontaneous copolymerization of equimolar amounts of TBA and PL.

M

1

Oligomer s t r u c t u r e

3

2

rel.

intensity

342

|-ALAL-|

74

342

r-AALIq

10

369

pAAAL-j

100

441

r-AAALL-|

468

pAAAAIq

98

441

|-AALAL-|

36

7

M = molar mass o f oligomer determined by CI-MS. A = amine u n i t ,

L = lactone u n i t .

from GC-MS using e l e c t r o n impact i o n i z a t i o n .

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

228

RING-OPENING

POLYMERIZATION

F i g u r e 5 . GPC a n a l y s i s of the r e a c t i o n products o f 1

equimolar amounts (0.1 m o l . l " ) of TBA and PL a f t e r 8 h r s a t 50° i n a c e t o n i t r i l e .

JVJ Retention time

F i g u r e 6 . Gas chromatographic formed from TBA and PL.

a n a l y s i s o f the oligomers

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

17.

GOETHALS ET AL.

Polymerization of Ν-A Ikylaziridines

229

In Figure 6, peaks nr. 1 and 2 correspond to oligomers containing two TBA and two PL units. Although the mass spectra could not be used to distinguish between the ALAL and AALL structural isomers, it is reasonable to assume that the much larger peak nr. 1 corresponds to the alternating oligomer since the occurrence of two adjacent PL units by homopolymerization is not very probable due to the low polymerization rate of PL at 25°C. The most abundant oligomers are the -AAAL- and -AAAAL- compounds (peaks nr. 3 and 5) which are 13- and 16-membered rings respectively. These are formed by a ring closure of the zwitterions AAALθ and AAAAL^. This confirms the assumption that in this copolymerization the TBA monomer is consumed in a considerable proportion by cationic homopropagation. This investigation is now continued with other N-alkylaziri­ dines and with pivalolactone. Literature Cited 1. 2. 3.

Goethals, E. J.; Munir, Α.; Bossaer, P. Pure & Appl. Chem. 53, 1753 (1981). Goethals, E. J. Proceedings of the 28 IUPAC Macromol. Symp., Amherst, 1982, p. 204. Le Moigne, F . ; Sanchez, J . Y.; Abadie, M. J. Preprints of the 6 Intern. Symp. on Cationic Polymerization, Ghent, 1983, p. 87. Maat, L . ; Wulkan, R. W. Rec. Trav. Chim. 100, 204 (1981). Razumova, E. R.; Kostyanovskii. Izv. Akad. Nauk SSSR, Ser. Khim. 9, 2003 (1974). Bottini, A. T.; Dowden, B. F . ; Van Etten, R. L. J . Am. Chem. Soc. 87, 3250 (1965). Jaacks, V.; Mathes, N. Makromol. Chem. 131, 295 (1970). Saegusa T.; Kobayashi, S.; Kimura, Y. Pure & Appl. Chem. 48, 307 (1976). th

th

4. 5. 6. 7. 8.

RECEIVED March 27, 1985

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

18 Block Copolymer of Poly(ethylene glycol) and Poly(N-isovalerylethylenimine) Kinetics of Initiation M. H. LITT and X. SWAMIKANNU Department of Macromolecular Science, Case Western Reserve University, Cleveland, OH 44106

We have investigated the molecular weight d i s t r i b u t i o n of a block copolyme ditosylate (MW 3500 polymerization of 2-isobutyl oxazoline ( l i v i n g polymer). In this system the rate of i n i t i a t i o n i s much smaller than the rate of propagation. This leads to the forma­ tion of a mixture ofdi-and t r i b l o c k polymers for monomer i n i t i a t o r r a t i o s ≤ 400. A theoretical model was developed to correlate molecular weight d i s t r i b u t i o n of this system. This was compared to the experimental gel permeation chromatography trace with the theoretical model modified to include the e f f e c t of the PEG central block, the spreading of the trace as i t went through the columns and the slope of the log MW versus retention volume l i n e . A good fit was found with ki/kp = 0.0070. When methyl tosylate was used to poly­ merize 2-isobutyl oxazoline, a similar treatment of the data showed ki/kp = 0.22. The effect of the PEG i s explained as due to solvation of the initial adduct by the neighboring ether group. 2-Oxazolines are known to undergo ring opening polymerization when i n i t i a t e d by acid catalysts (1-4). The polymerization proceeds through l i v i n g oxazolinium ion; i n the absence of chain transfer and termination and when the i n i t i a t i o n i s instantaneous, the polymer produced would be monodisperse (5). Alkyl esters of p-toluenesulfonic acid have been used to i n i t i a t e the polymerization of 2-oxazolines (6-8). Bifunctional toxylate i n i t i a t o r s have been used (9-10) to prepare triblock copolymers of 2-oxazolines. We wanted to prepare monodisperse triblock polymers of controlled block lengths of poly(Nisovaleryl ethyleneimine) (PiVEI) from 2-isobutyl oxazoline and poly (ethylene glycol) (PEG), using PEG ditosylate as i n i t i a t o r . It was found that at small monomer/initiator r a t i o when all the monomer had been consumed, unconsumed i n i t i a t o r was still present. The present paper describes the synthesis and characterization of a triblock copolymer. A theory was developed to predict the molecular weight 0097-6156/85/0286-0231$06.00/0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

232

RING-OPENING POLYMERIZATION

d i s t r i b u t i o n of the block copolymer and evaluate the r e l a t i v e rates of i n i t i a t i o n and propagation for the PEG ditosylate/2-isobutyl oxazoline system. A similar study was made f o r the methyl tosylate/ 2-isobutyl oxazoline system. Experimental 2-Isobutyl oxazoline; This was prepared by the method of Kaiser (11) b.p. 160°C/760 mm Hg ( l i t (6), b.p. 76°C/40 mm Hg). The structure was confirmed by 1H NMR and IR spectroscopy. PEG d i t o s y l a t e : The synthesis of pure PEG ditosylate (MWt = 3500) i s described b r i e f l y . The f u l l procedure i s given elsewhere (12). PEG 3500 (Dow Chemical) was p u r i f i e d by treatment with NaBH^ i n absolute ethanol followed by several r e c r y s t a l l i z a t i o n s from absolute ethanol at 4°C. The tosylate was prepared using the Schotten-Bauman proce­ dure: p-toluenesulfony lene glycol) at 0°C. Polyme ethanol at 4°C. Four r e c r y s t a l l i z a t i o n s gave pure polymer with 2.0 tosylate groups per chain as determined by ^H NMR, IR and UV spectros­ copy. The PEG ditosylate had the same degree of polymerization as the s t a r t i n g d i o l , as found by gel permeation chromatography. Preparation of the copolymer and the homopolymer: Polymerizations were run under vacuum i n ampoules f i t t e d with high vacuum Teflon stopcocks. Table I l i s t s the amounts of i n i t i a t o r s , monomer and solvent, (o-dichlorobenzene). Solvent and monomer were d i s t i l l e d under reduced pressure into the ampoule containing i n i t i a t o r . After degassing, the ampoules were heated at temperatures and times given i n Table I. The ampoules were removed and samples were taken for GPC. Polymers were isolated by p r e c i p i t a t i o n into mixed hexanes ( b o i l i n g range 38°-55°C) dried at 60°C. Yields were quantitative except f o r small handling losses. 2.45 of the product from run 1 was s t i r r e d twice with 10 ml. of acetone and the undissolved polymer was sepa­ rated from the supernatant by décantation. The polymer was dried under vacuum (< 1mm Hg) at 60°C. Y i e l d 2.15 g. X

H NMR (CDC1 ) of the copolymer:

6 3.65 (s,-OCH CH ), 6 3.45

3

2

2

(broad-NCH CH -) , δ 2.2 (broad, (-O^CHXCH^^ , 6 0.92 (d, (CH ) CHCH -). 2

2

3

2

2

Table I. Polymerization Conditions Run

Initiator, g

Monomer, g

M/1

Solvent/ml

T,°C

Time

10 14

100 130

4 h. 10 min.

0

1 2

PEGTs, 0.952 MeOTs, 0.927

2.4 3.75

38 5.92

Gel permeation chromatography: Molecular weights of the polymers and their d i s t r i b u t i o n s were measured using a gel permeation chromatograph, with THF as the elution solvent. The GPC was equipped with a d i f f e r e n t i a l refractomonitor, Model LDC 1107 and a UV (254 nm) absorance meter, Model 153 (Beckman), i n s e r i e s . The GPC traces given i n

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

18.

PiVEI-PEG Block Copolymer

LITT AND SWAMIKANNU

233

Figure 1 were obtained using μ-Spherogel (Altex) columns of nominal p o r o s i t i e s IQ4, 10 , and 500A and a 100Â u-Styragel (Waters Assoc.). The GPC trace i n Figure 2 was obtained using y-Styragel columns of p o r o s i t i e s ifjS, 10^, and -±$3 £ μ-Spherogel columns of p o r o s i t i e s 500 and 100 £ and a 100 Â Ultrastyragel column were used to obtain the GPC trace i n Figure 3. The GPC columns were calibrated with monodisperse standards of polystyrene and polyethylene g l y c o l . Mn and Mw were calculated using Μη = ZHi/lHi/Mi and Mw = EHiMi/ ZHi where Hi i s the height of the GPC trace at a given e l u t i o n volume and Mi the corresponding molecular weight. The l a t t e r was obtained from the c a l i b r a t i o n curve. Heights were taken at equal i n t e r v a l s (0.2 ml). The r a t i o of peak i n t e n s i t i e s of UV and ARI peaks (UV/ARI) was used as a measure of UV absorbing (e.g., tosylate) f u n c t i o n a l i t y of the materials. The area-to-mass r e l a t i o n s for the homopolymer and methyl tosy­ l a t e were obtained from the areas under the GPC traces (ARI) of solutions having known concentration MeOTs. Areas were measure *H NMR spectra were obtained on a Varian EM360 or an A60, 60 MHz spectrometer i n C^D^, CDCI3 or o-C^H^C^ solutions. TMS was used as an i n t e r n a l standard. For infrared spectra, thin films of the samples were cast from C H C I 3 solution on NaCl plates and the solvent evaporated under vacuum. Spectra were recorded on a Digilab FTS 14 FTIR spectrophotometer. 3

#

Results Synthesis of block copolymer: GPC analysis of the polymerization solution indicated that a l l the monomer was consumed. The presence of unconsumed i n i t i a t o r was observed. PEG tosylate eluted at 26.2 ml and had UV/ARI of 8000. The chromatogram of a solution of run 1 i s given i n Figure l a . The peak at 24.2 ml corresponds to that of the block copolymer. The peak at 26.2 ml has UV/ARI ^ 8000 and should be the unreacted PEG d i t o s y l a t e . Figure l b shows the e l u t i o n p r o f i l e of the of the acetone-washed copolymer and i t i s free from PEG tosylate. The presence of unconsumed i n i t i a t o r indicated slow i n i t i a t i o n . Also, since the two ends of PEG tosylate are i d e n t i c a l i n r e a c t i v i t y by random s t a t i s t i c s (12) we expect the copolymer to be a mixture of ABA type t r i b l o c k ( i n i t i a t i o n at both ends) and AB type diblock ( i n i ­ t i a t i o n at one end) copolymers. This was observed, as shown by the s o l i d l i n e of Figure 2 when the copolymer was eluted through a d i f f e r e n t combination of columns. The peak at 24.0 ml corresponds to the t r i b l o c k copolymer and the peak at 25.4 ml corresponds to the diblock copolymer. Composition of the block copolymers: The average lengths of the PiVEI blocks was obtained from 1H NMR spectroscopy on the acetone washed copolymer. The PEG CH2 s have a sharp resonance at δ 3.65 ppm and the methylene protons of the PiVEI part occur as a broad peak centered at δ 3.45 ppm which overlaps the PEG resonance. The areas under these peaks were separated as follows. The protons of (CH3) of the PiVEI occur as an isolated doublet at δ 0.92 ppm. Since there are s i x methyl protons for four >N-CH2CH2~ protons i n PiVEI, the area of >ΝΟΗ ΟΗ - i s two-thirds the area of the methyl f

2

2

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

234

RING-OPENING POLYMERIZATION

22 23 24 25 26 27 E l u t i o n Volume, ml 21

22

23

24

25

26

27

28

I I I I I I II

10 8

10

Ηπ(ΡΕΟ) χ 10 3 r

8

4

IMPEO) x io"

3

Figure 1. GPC traces of (a) copolymer 1 and (b) acetone-washed copolymer 1. Columns used: Ι Ο , 10 , 500 A ySpherogel and 100 A yStyragel. 4

3

22 23 24 25 26 27 E l u t i o n volume, ml



—T"

100

50

1

ι

τ

20

10

2

MN(POLYSTYRENE) χ 10° Figure 2.SiCl

SSiCl

CH,

CH =CH/0) ι 2

H

? 3 sicl

J

2

3

3

2

2

3

3

3

3

CH, ι 3 CH, ι3 CH,Si(OSi),OLi CH CH

3

ÇH CH CF CH SiOLi CH,

CH,SiOLi ι CH,

H

? 3

2

CH CH CF CH,SiOLi >ι CH,

3

CH, ι -J CH^SiOLi ι •CH,

3

ÇH SiCH CH, 3

3

I

3

I

3

3

2

2

3

I

3

4

I

3

CH, CH,

2

CH =CH

>

ι

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

2

Ο

II

2

3

CH,

2

H PtCl

6

o

C H

3

I

3

I

CH.

ι

ι

, J ι J

CH, CH,

CH,

CH

J l

3

CH

CH

J

b

c

CH

i

3

-

0

C H

3 0

I

J I

J

CH,CH,

H

2

3

3

3

3

CH =CCO(CH )_ Δ ι, Z D SiOSiCH. CH CH

3

J

CH

3

;

CH

3

7

CH

3

Δ

CH =CC0(CH,) (SiO) S i C H , 2 5 ' ι II 0 CH, CH. o

3

CH, 73 ? 3 I CH. =CCO(CH,) (SiO) ,SiCH. 2'5 ι n CH, CH, CH, Ο ^3 ι 3 CH.Si(OSi),OLi ι CH, CH, '3 ï"3 ^ 3 CH- CH. CISi(OSi),OSiCl ι ι I CH CH CH.

CH

ι

CH.,Si (OSi) ,OLi

J

CH. CH, CH, , 3 , J , i CISi (OSi) SiCH.

MS i C l

LiAlH.

Ο

HSi(OSi).OSiCH, , 6 ι 3 CH- CH-

2

H PtCl

3

I CH,=CC0(CH )-SiCl Z n ^ b|

I

CH.

H

(mmol/1)

Yield(%)

79

3 .00

2 .80

3 .00

1 .07

M n , c a l c Mn,UV 3

(xl0~ )

Mn,VPO 3

(xl0~ )

f

3

(xl0~ )

SMI

0 .911

63 .3

SM2

0,.613

40 .

0,.651

21 .7

85

6..30

6,.70

5 .90

0,.88

0..651

21,.7

85

6..30

6..60

5,.90

0,.89

1..00

28..9

94

8..00

7..60

5,.50

0..72

0.,534

32,.8

76

3.,90

3.,70

3..80

1..03

1. 04

43.,3

83

5. 70

6.,40

5..40

0..84

0. 499

28. ,0

90

4.20

4. 15

4.,20

1.,01

1. 181

27. 8

90

8. 80

9. 07

8. 96

0. 99

SM3 C

SM4 '

d )

MM5 MM6

C)

MM7 MM8 MM9

C)

C)

a) P o l y m e r i z a t i o n s were c a r r i e d with b)

t h r e e - f o l d excess

o u t a t 0°C i n THF, and t e r m i n a t e d

SSiCl(SM-series) o r MSiCl(MM-series).

f=Mn,VPO/Mn,UV

c) Under u l t r a s o n i c

irradiation.

d) F u n c t i o n a l i z a t i o n by S S i C l was s a t i s f a c t o r y c o n c e n t r a t i o n o f LTMS was k e p t and

any s i g n i f i c a n t

h i g h e r than

as long as t h e about

30 mmol/1,

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

observed.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

19.

KAWAKAMI A N D YAMASHITA

Polysiloxane Macromers

251

minutes seemed s u f f i c i e n t , and f u n c t i o n a l i t i e s approached unity. These results are shown i n Table I. Macromers of Mn-9,000-10,000 could be easily obtained by manipulating the monomer/initiator r a t i o . The presence of the terminal unsaturation i n the macromers was confirmed by ^H-NMR, IR, and by UV. These macromers had a quite narrow molecular weight d i s t r i b u t i o n s . Copolymer Synthesis. The conditions used for the synthesis of copolymers and the characterization data of the copolymers are presented i n Table II with some results of homopolymerizations. The combination of GPC and Ï-H-NMR was helpful i n showing the e f f e c t i v e incorporation of the macromer units into the copolymers. The molecular weights of the graft copolymers were not very high. Consequently, the number of the grafts attached to a given backbone i s generally small. The monomer r e a c t i v i t y ratios of conmonomers i n the copolymer­ i z a t i o n with s t y r y l typ seem to have similar r e a c t i v i t copolymerization. (13-15) Film Forming and Surface Active Properties of Graft Copolymers. The use of tailor-made graft copolymers i n the surface modifications of polymers i s quite promising because of their e f f i c i e n c y and also because the graft copolymer structure can be varied for any particular application.(4^-8) A l l the graft copolymers (#13-17 i n Table I I ) , despite their rather low molecular weights, are capable of forming transparent, although b r i t t l e , films. Binary blend films were prepared by casting the blends of siloxane polymers with polyMMA or polySt. The content of the siloxane polymers varied from 0.1-10%. The surface active properties were evaluated/measured by changes i n the contact angle of the water droplet placed on the a i r side surface and glass-side surface of the films. For the comparison of the e f f i c i e n c y of the surface modification, the results of random copolymers and homopolymers are also shown i n Figure 1. An examination of the results shows that the siloxane polymers exhibit pronounced surface accumulation on that side. It can be seen that quite small amounts of siloxane polymers, e.g. 0.51.05 depending on their siloxane contents (except polydimethylsiloxane), are capable of producing s u f f i c i e n t surface enrichment and therefore appreciable hydrophobicity on that side of the f i l m . However, on the glass side, the contact angle v a r i a t i o n i s not much, indicating the enrichment of siloxane polymer might be suppressed. This i s i n keeping with the well known hydrophobic nature of the siloxanes. FTATR-IR and ESCA Measurement. In order to know the d i s t r i b u t i o n of the graft copjolymer in the blend f i l m , i t i s necessary to estimate the concentration at different depths. This can be achieved by employing different spectroscopic methods detecting at different depths. FTATR-IR i s one of these spectroscopies. Although the s e n s i t i v i t y i s not so high, the average concentration of graft copolymers to about 5,000 Â and 15,000 Â depths from the surface can be estimated by changing the prism for the blend system containing

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

S8, 25

9

99 .3

97 .8

98 .9

99 .6

17 M120, 0.4 MMA,

h)

16 M l 2 0 , l . l MMA,

st, 97 .8

M60, 0.7 MMA,

14

M60, 2.2

-

st, 36

M60, 2.2 MMA,

15

S8,100

-

-

M120, 0.3 MMA,

M120, 0.8 MMA, 99,.7

99 .2

st, 97,.3

99 .4

98 .4

st, 40

-

st, 87

st, 77

-

st, 80

St, 61

FA, 41

M60, 0.6 MMA,

M60, 2.7

FA, 15

M60, 1.6 MMA,

M5, 60

M5,100

S8, 13

S8, 23

S5, 20

S5, 39

S5, 59

S5,100

S2, 85

S2,100

SI,100

composition ' monomer—comonomer (mol %) (mol %)

80

60

st, 75

St,

St,

FA, 44

13

h)

M5, 64

S8,100

8

12

S5, 20

7

M5,100

S5, 40

6

11

S5, 56

5

-

FA, 10

-

12. 5 S t , 87 .5

S5,100

4

f

S2, 90

3

S8

S2,100

2

10

31,100

teed monomer—comonomer (mol %) (mol %)

1

No.

Table I I . Copolymer Syntheses

Y

l

d

57

60

60

58

89

58

38

90

73

64

83

94

71

90

96

(%)

e

55

60

i

__. ., w w

5.6

8.4

5.8

6.1

7.8

12.5

24.2

13.4

5.1

12.8

31.7

15.6

6.6

34.9

16.5

23.8

54.4

4

C)

xlO"

M

M

n

M

c)

3.2

5.8

4.0

3.1

4.2

8.1

8.4

5.3

2.7

6.4

6.5

7.3

2.1

9.6

6.7

8.4

27.4

w

4

w

xlO"

w /

1. 45

1. 96

1. 84

1. 55

2. 87

2.,51

1. 88

2.,00

4..90

2,.14

3,.12

3,.64

2 .47

2 .78

1 .74

n

. c)

1. 73

1. 46

M

S

0.4

1.0

1.6

0.4

1.0

3.0

5.0

1.0

1.8

8.0

1.0

2.0

3.0

5.0

1.7

2.0

1.0

number

23

41

53

21

41

42

70

39

52

85

41

58

41

78

45

59

41

(wt %)

Appear-

0.7

2.7

4

1.5

4

-

Ρ

Ρ

Ρ

Ρ

Ρ

w

w

Ρ

w

V

Ρ

w

w

w

w

Ρ

Ρ

g r a f t s ance

„.d) o) S i l o x a n e no of

l

f

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

BTM, 20

SF2 100

FS2,100

FF2,100

22

23

24

25

at

FF2,100

FS2,100

SF2,100

BTM, 16

MTS, 30

MTS, 12

MTS,100

70

88

-

FA, 84

MMA,

MMA,

-

60°C i nι THF with AIBN as an

-

FA, 80

70

37.3

31.0

29.7

n

CH, ι3

3

C H

3

3

weight percent i n polymer.

2.0

2.0

2.0

0.5

4.0

1.8

1.0

4.0

% to monomer)

2.12

1.96

1.84

-

1.83

1.41

1.36

2.20

h) M60 and M120 are macromers from No. MM8 and MM9 i n Table 1, r e s p e c t i v e l y .

g) Weight percent i n c l u d i n g f l u o r o p r o p y l groups.

f) p=powdery, w=waxy, v=viscous o i l .

C H

(SiO) _^SiCH

e) CH. ι 3

d) Number o f s i l i c o n atoms per monomer u n i t .

17. 6

15. 8

16. 1

4.0

12. 3

10. 2

12.,5

i n i t i a t o r ( 0 . 1-0.2 mol

68

56

77

-

7.3

84

17.3

13.8

27.5

68

85

78

c) Determined by GPC and c o r r e l a t e d t o standard p o l y S t .

b) Determined by NMR.

a) Polymerized

/

Polydimethylsiloxane

21

MMA,

MTS, 30

88

20

MMA,

MTS, 12

19

-

MTS,100

18

g)

7 4

g)

68^

68

13

100

45

25

70

w

Ρ

Ρ

w

ν

Ρ

Ρ

w

RING-OPENING POLYMERIZATION

254

Table I I I . Monomer Reactivity i n the Copolymerization of Polysiloxane Macromers Macromer(A),

Mn

Comonomer(B)

«J-Stylyl p o l y s i l o x a n e , 3,400 6,700 a)

r

A

and

r

f î

t

MMA

a r e monomer r e a c t i v i t y

weight analogue p a i r s

001

S

0.05

0.1

taken

from

0.5

B 1.1

'a) A KSt)

'a) Β l(St)

0.60

0.52(St)

0.461MMA)

r

r

r a t i o s o f low

r

molecular

Polymer Handbook.

10

5.0

100150

Siloxane Content(wt*/#) in the Blend Figure 1.

Contact Angle of Water Droplet at 20°C for Various Siloxane Polymers-PolyMMA Blend Films. : GM211, : GM213, : GM411, : GM413, V: poly-MTS, Δ: MTS25, Δ: MTS45, V: polyDMS are copolymers and polymers synthesized i n Nos. 13,14,16,17, 18,19,20, and 21, respectively i n Table I I .

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

19.

KAWAKAMI AND YAMASHITA

Polysiloxane Macromers

255

10% w/w graft copolymer. The results are shown in Table IV. Contrary to the results of contact angle measurement, by which higher concentration of graft copolymer on the a i r - s i d e surface was c l e a r l y seen even at the concentration of 0.1% graft copolymer, concrete differences between the surfaces of the two sides to 5,000 Â could not be observed u n t i l the concentration of 10% graft copolymer reached. However, the measurement to 15,000 Â depth c l e a r l y indicated that even at the a i r - s i d e surface of the modified polyMMA film by adding 10 wt% graft copolymer, the average concentration to 15,000 Â depth from the surface i s much lower than that to 5,000 Â as shown i n Figure 2. This fact suggests that at the concentration of 10 wt% graft copolymer to bulk polyMMA, the graft copolymer may exist between the surface and about 10,000 Â depth, and the r e l a t i v e concentration i s i n the order: a i r - s i d e surface > glass-side surface »

inner part of the film

Information close measurement. The results, with Al Kal,2 source which gives the average concentration to about 20 Â depth, are shown i n Figure 3. Although there i s some scatter of the measured points, the results are consistent with the contact angle data at the points that the graft copolymer concentration at a i r - s i d e surface i s higher than that at the glass-side surface, and that the change in the concentration at the glass-side surface i s smaller compared to a i r side surface. Furthermore, the concentration of the graft copolymer at both surfaces are higher than the average concentration of the graft copolymer in the bulk, which was calculated from the weight percent of the added graft copolymer, detected by ESCA. From the results mentioned above, the following picture of how the graft copolymer exist in the blend may be proposed. 1. Polysiloxane graft copolymers phase-separate to both a i r - and glass-side surfaces. The concentration of graft copolymers seem to be higher near the surface. 2. At the a i r - s i d e surface under surface active condition, the polysiloxane graft copolymers w i l l accumulate at the surface resulting in sharp change i n contact angle and ESCA. At the glass-side surface, although the bulk concentration of the graft copolymer seems to be similar to that at the a i r - s i d e surface, the concentration at the skin of the surface seems different from that at the inner of the surface layer. The polar groups (presumably carbonyl groups of methyl methacrylate comonent) might be oriented near the surface by the influence of glass surface environment. This seems to be reflected i n the s l i g h t change i n contact angle measurement at the glass-side surface. FTATR-IR can not distinguish the difference in concentrations at such shallow layer. Durability of Surface Modification toward n-Hexane Treatment. The d u r a b i l i t y of such surface modification i s very important from a p r a c t i c a l view point. Thus, there may be some chance of loss of the surface-modifying polysiloxane component from the surface under

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

256

Table IV. ATR-IR Relative Absorbance of Various PolysiloxanePolyMMA Blend Films. )

GM4lf/ PolyMMA

(%)

A79#A740

b

)

Air-Side

Glass-Side

0.1

0.30

0.22

0.5

0.27

0.28

1.0

0.44

0.43

2.45

2,10

0

10.0 10.0

c )

1.48

) GM411 i s the g r a f t copolymer

synthesized i n No.

16 i n Table I I . b) The absorptions a t 740 and 795 cm""*" are c o u p l i n g o f CH

2

and s k e l t a l v i b r a t i o n i n polyMMA u n i t s ,and

SiCH^ r o c k i n g modes, r e s p e c t i v e l y . The s p e c t r a were recorded on Ge prism. c) Recorded on KRS5 prism.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

KAWAKAMI AND YAMASHITA

257

Polysiloxane Macromers

SiÇrtyGMAU)

CHo versus t£-ti showed a linear relationship, from which k values were obtained. Arrhenius plots of k values at four temperatures gave a straight line whose slope led to the a c t i v a t i o n parameters (Table I) (16). 1

p

p

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

298

Table I . Propagation Rate Constants and Activation Parameters i n the Polymerization of \^

k

χ 10*

Initiators PhCH Br

MeÔtf

Iter

3·52(50°Ο

4.53 (50°C)

PhCH^Cl

2

e

2.13(70°C)

1.88(130 C)

4.34(80°C) 7.99(90 C) 15.0(100°C)

3.89(140 C) 5.45(150 C) 10.5 (160 C)

Ρ (L/mol.sec)

e

9.27(60 C) 24.3 (70 C) 40.3 (80°C) e

e

k_x 10*(50 C) tL/mol.sec)

11.5 25.0 43.8

3.52

ΔΗ±(50°Ο (kJ/mol)

(60° C) (70°C) (80 C) e

4.53

e

(0.475)

b

e

e

e

(0.00538)

b

73.3

-84.8

e

AS±(50 C) (J/K.mol)

-103

-136

-132

a) [M] =1.25 mol/L and [l] » 0.125 mol/L i n PhCN solvent. e

e

b) Calculated values.

J i

Alkyl Halide Initiated Systems. Figure 2 shows the P NMR spectra of the polymerization system i n i t i a t e d by Mel i n PhCN. Peak assignments were made as c i r c l e d l e t t e r s i n Scheme II and led to the generalpolymerization mechanism (Scheme I I ) . No signal due to phosphonium species was detected under the polymerization conditions employed. This i s i n sharp contrast to the MeOTf-initiated system. Intermediates ^ and ^ are unstable. The stable propagating ends

Scheme I I Initiation RX slow R=Me, PhCH

/

\_

Ph

18 2

> R-PCH CH2CH X ^ 2

fast

p

©

h

19

X=I, Br, CI

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

2

22.

Electrophilic Polymerization: A Novel Mechanism

KOBAYASHI

Figure 2.

299

31p {lfl} NMR spectra of the cationic ring-opening polymerization of 1 i n i t i a t e d with MeI([M] * 1.25 mol/L and [ I ] = 0.125 mol/L): (a) after 1 min at 70°C; (b) after 10 min at 70°C; (c) after 20 min at 70°C. Reproduced with permission from Ref. 15. Copyright 1984, American Chemical Society. Q

0

®

Ph

&p, slow

20

«

0

0

II

II

* Me — PCH CH CH -ePCH CH CH - -)—PCH CH CH I / I /*\ n/l I I I fast 2

®

P

h

9

2

9

2

0

®

2

P

0

2

0

2

0

9

0

0

h

22 are a l k y l iodide species l i k e ^ M , and The rare-determining steps of both i n i t i a t i o n and propagation are the dipole-dipole S 2 reactions between and a l k y l iodide and monomer 1 producing transient phosphonium species such as 18 and 21, which are converted rapidly into covalent a l k y l iodide species ^ N

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

300

RING-OPENING

POLYMERIZATION

and ^ v i a nucleophilic attack of the iodide counteranion. From the plots of the second-order kinetics of Equation 1 k values were obtained. S i m i l a r l y , benzyl bromide and benzyl chloride were also found to proceed via a l k y l halide propagating ends as stable species. These k i n e t i c results are given i n Table I (16) . The k values are very much dependent upon the counter-anion derived from i n i t i a t o r . The r e l a t i v e r e a c t i v i t i e s at 50°C are in the following order; MeOTf : Mel : PhCH Br : PhCH Cl = 654 : 842 :88.3 : 1.0. The polymerization of proceeds via two different mechanisms which i s due to differences in the n u c l e o p h i l i c i t y of the anions TF0~ and Χ" (X = I, Br, CI), which affect the r e l a t i v e s t a b i l i t y of the phosphonium species. The difference i s reflected by AS* values; the reduced polymerizability of the PhCl^Br or PhCI^Cl system i s attributed to the less favorable entropy term i n comparison with the MeOTf system. This can be interpreted i n terms of solvationdesolvation phenomena from the i n i t i a l state to the t r a n s i t i o n state (16). In ring-opening polymerizations species are usually more reactive than covalently bonded ones, eg, superacid macroestertype species in c y c l i c ether polymerizations (17,18) and a l k y l halide type species i n 2-oxazoline polymerizations (19). It i s to be emphasized, however, that the Mel-initiated polymerization of ^. proceeds even faster than the MeOTf-initiated system, although the difference i s small. This i s the f i r s t case of covalent ( e l e c t r o p h i l i c ) propagating species showing a higher r e a c t i v i t y than an ionic propagating one (16). p

p

2

2

l-Phenyl-3H-2,1-benzoxaphosphole (2) Ring-Opening Polymerization. Monomer 2 i s a five-membered c y c l i c phosphinite, an analogue of dexophostone ^. ^ was prepared according to the reported procedure (20). The ring-opening polymerization of 2 produced white powdery materials of poly(phosphine oxiâe ) J ^ , whose structure was determined by IR, 31p, 1 and C NMR spectroscopy as well as by elemental analysis. The polymerization results are given i n Table II (21). H>

0

R

23

+

O - i

24(R=Me, E t ; X=BF , TfO) 4

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

22. KOBAYASHI

Electrophilic Polymerization: A Novel Mechanism

Table I I . Ring-Opening Polymerization of 2

Initiators (mol % f o r 2)

Solvents

E t 0 BF "(17)

CH C1

MeOTf(19)

CDC1

Temp. («c)

Time (ht)

a

Polymer Yield(%) Mol. wt.

35

48

0*

3

35

24

0

Mel(21)

CH CN

35

24

91

Mel(18)

CDC1

35

24

100

Mel(1.4)

CHCI3

35

1440

63

MeOTf(5.0)

CH C1

Mel(5.0)

PhCN

50

3

53

Mel(10)

CH C1 2

2

70

16

67

none

CH C1 2

2

70

16

0

none

CH C1

2

130

14

54

3

4

2

2

3

3

2

2

301

b

4500

2

2400

2260

a) 2(0.3 g) i n 1 mL of solvent i n a sealed pressure under nitrogen. b) Stable phosphonium species 24 was formed. Among the cationic i n i t i a t o r s examined, only Mel i s active f o r the polymerization. Et30 BF4~ and MeOTf produced stable phosphonium s a l t s 24^ which did not induce the polymerization of 2. Anionic and r a d i c a l i n i t i a t o r s were inactive. At higher temperatures, eg, above 70°C, 2 starts to show polymerizability without i n i t i a t o r to give polymer of the same structure as 23. The mechanisms of this "thermal" polymerization i s not wêîl understood, but, at present, a zwitterion intermediate ^ derived from two molecules of ^ i s considered to be responsible for the production of polymer 23. The +

"0-P

7-=-r

CH,—P.

—2îL*

25 formation of 25^ requires that one molecule of ^ acts as a nucleophile and the other behaves as an e l e c t r o p h i l e . This "amphip h i l i c " nature of £ has already been confirmed i n the copolymerizations, i n which 2 was copolymerized without i n i t i a t o r with an e l e c t r o p h i l i c monomer l i k e a c r y l i c acid and with a nucleophilic one l i k e 2-methyl-2-oxazoline (22).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

302

RING-OPENING POLYMERIZATION

Kinetics of E l e c t r o p h i l i c Ring-Opening Polymerization of 2^: A New Mechanism i n Ionic Polymerizations. The kinetic analysis of the polymerization i n i t i a t e d with Mel was carried out by * l p NMR spectroscopy at 35°C, at which the thermal polymerization does not take place at a l l . Figure 3 shows a ^ l p NMR spectrum of the polymerization system i n ΟΗβΟΝ, i n which a r e l a t i v e l y large amount of the i n i t i a t o r was employed for the kinetic analysis. Peak A at 119 ppm i s assigned to monomer 2. Peaks due to phosphonium species appear over a wide chemical s h i f t range: peak A at 95 ppm i s attributed to the phosphonium iodide and peaks C around 67 and 83 ppm are due to phosphonium iodides l i k e 28^ ^1, and Peaks D are ascribed to various phosphine oxide units including propagating ends such as 27^ and 30^, i f any (Scheme I I I ) .

A B

1

— —/ / — 120 Figure 3.

1

«—-y μ

90

70

1—

40

30

(ppm)

3 1

P {^-H} NMR spectrum of the Mel-initiated polymerization of 2 after 490 min at 35°C i n C H 3 C N . [M] « 1.0 mol/L and [ I ] = 0.20 mol/L. Q

0

Scheme I I I

Initiation 0 II

Me-P-

-CH I 2

k 27(P

x c l

)

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

22. KOBAYASHI

Electrophilic Polymerization: A Novel Mechanism

303

Figure 4 shows the time-conversion curves for monomer £ and the t o t a l concentrations of active species [P*]. The following [P*] = [P*i] + [P* ] c

r e l a t i o n s i p holds where [P*i] and [P* ] are the concentrations of phosphonium species and of covalent a l k y l iodide species, respectively. The i n i t i a t i o n finished at an early stage of the reaction. Under the polymerization conditions i n CH3CN [P*i] reached a constant" value that was almost equal to the concentration of the i n i t i a t o r charged, i e , [P*] = [P*i] · After [P*i] became constant, the apparent rate constant of propagation (kp(ap)) obtained based on Equation 1. The values are very mucn dependent upon the solvent employed (Table III) (23). In a highly polar solvent (eg, CH3CN) kp(ap) value i s at least 102 times less than that i n a less polar solvent (eg PhCl) c

w

a

s

1.0

£N 0.8 —.

Monomer

Ο

Ε ο.β ϋ § 0.4

ϋ 0.2 100

200

300

400

500

Time(min) Figure 4.

Time-conversion curves for monomer 2 and t o t a l active species [P*] (=[P*il) i n the polymerization of 2 with Mel i n i t i a t o r at 35°C i n C H 3 C N . [M] = 1.0 mol/L and [ I ] = 0.20 mol/L. Q

0

These observations lead to the propagation mechanism shown i n Scheme I I I . The phosphonium species ^ and ^ are reasonably considered as "not r e a l l y active", which i s supported by the fact that phosphonium salt did not i n i t i a t e the polymerization.

Table ΠΕ. Values of k , > with Mel I n i t i a t o r i n Three Solvents at 35°C ρ Cap) Solvents k , ,(L/mol«sec) p(apj CH CN

7.3 x 10"

5

PhCN

7.6 x 10"

4

PhCl

>1

2

3

x 10"

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

304

RING-OPENING POLYMERIZATION

Propagation

32

Me-PI Ph

Ο

p h

'

CH I 2

-» 23

27(really active)

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

306

General Scheme of the New E l e c t r o p h i l i c Ring-Opening Polymerization. The new polymerization i s given as the following general scheme (Scheme IV).

Scheme IV

+ monomer S 2 type propagation

-> Ρ

N

"Pro-active species

"Real a c t i v e " species

1

S i type r e a c t i o n

In order to evaluate for the S i reaction, an attempt was made to perform kinetic analyses based on Scheme IV. The rate equations for the monomer consumption and the production of [P* ] are given by Equations 3 and 4. N

c

d[M] — - - kp(c)[P*cl[M] at

(3)

d[P* ] c

kl[P*i] " k

dt

p ( c )

(4)

[P* ][M] c

In a highly polar solvent the relationship (5) w i l l be v a l i d after the i n i t i a t o r i s completely consumed [P* ] + [P*i] = [P*] = [ I ] c

(5)

0

where [ I ] denotes the concentration of the i n i t i a t o r charged* I t was impossible to determine [P* ] precisely. I t i s observed i n Figure 4 that the polymerization stage where [P*i] • constant i s present. Therefore, an assumption that [P* ] i s constant i s made. Then, d[P* ]/dt = 0, leading to [P* ] - k [ I ] / ( ^ p ( c ) [ l + l ) which i s v a l i d at a limited stage of polymerization. Equation 3 i s then expressed as d[M] Mk [I] [M] Q

c

c

M

c

c

p ( c )

d t

x

k

0

0

+

M O M

k

l

The integrated form of this equation i s given as [M]

t2

In

+ k

p ( c )

[I] (t -t ) 0

2

1

k

x

= kp

( c )

44

~-~P-0(CH -)—I 0

45

For comparing the polymerizability of the seven-membered monomer £ with that of the corresponding six-membered one (2-phenyl-

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

22.

KOBAYASHI

311

Electrophilic Polymerization: A Novel Mechanism

1,3,2-dioxaphosphorinane, 44), the polymerization of 44 was examined. It has been founâ' that the Mel-initiated polymerization of 44 produced polymer having a "normal" polyphosphinate structure containing no "isomerized" units and that a stable propagating species i s an a l k y l iodide 45. A k value obtained i s 1.34xl0~ L/mol-sec at 95°C i n CHCl .'^rhe se results indicate that a sevenmembered c y c l i c phosphonite 6 i s 1.9 times more reactive i n polymerizability than i t s six-membered analogue 44 (28). \J\l 2-Phenyl-l,3,6,2-trioxaphosphocane(7) 3

p

3

r

An eight-membered c y c l i c phosphonite 7 has been shown to polymerize v i a ring-opening with a cationic i n i t i a t o r such as PhQ^Cl and MeOTf (29). The P h C ^ C l - i n i t i a t e d polymerization produced a polyphosphinate 46 (molecular weight • 2800), containing mainly "normal" units, but the MeOTf-initiation gave 46 containing 34% "isomerized" units.

0 il

Ph-Pf

0.

-POCH CH OCH CH ~

\o

2

2

2

2

Ph

46

With the PhCh2Cl-initiated system, propagating species are of a l k y l chloride type 47. Kinetic analyses f o r the P h C ^ C l - i n i t i a t e d reaction at 150°C in^ftiCN give a k value of 2.8xl0" L/mol«sec. The reduced polymerizability i s due to the structure of an electronwithdrawing 2-alkoxyethyl chloride type of 47 (29). \j\> — 4

p

r

0 II —POCH CH OCH CH Cl 2

2

2

2

Ph

47 Literature Cited 1. 2.

McManimie, R. J . U.S. Patent 2 893 961, 1959. Petrov, Κ. Α.; Nifantev, Ε. E.; Khorkhoyanu, L. V.; Merkulova, M. I.; Voblikov, V. F. Vysokomol. Soedin. 1962, 4, 246. 3. Mukaiyama, T.; Fujisawa, T.; Tamura, y.; Yokota, Y. J . Org. Chem. 1964, 29, 2572. 4. Shimidzu, T.; Hakozaki, T.; Kagiya, T.; Fukui, K. J . Polym. S c i . Part B. 1965, 3, 871. 5. Shimidzu, T.; Hakozaki, T.; Kagiya, T.; Fukui, K. B u l l . Chem. Soc. Jpn. 1966, 39, 562. 6. Fujisawa, T.; Yokota, Y.; Mukaiyama, T. B u l l . Chem. Soc. Jpn. 1967, 40, 147. 7. Harwood, H. J . ; Patel, Ν. K. Macromolecules 1968, 1, 233. 8. Yamashita, Y. J . Polym. S c i . Polym. Symp. 1976, 56, 447. 9. Vogt, W.; Ahmad, N. U. Makromol. Chem. 1977, 178, 1711. 10. Kawakami, Y.; Miyata, K.; Yamashita, Y. Polym. J . 1979, 11, 175.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

312 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

Petrov, Κ. Α.; Nifantev, E. E.; Sopikova, I. I. Vysokomol. Soedin. 1960, 2, 685. Singh, G. J . Org. Chem. 1979, 44, 1060. Kobayashi, S.; Suzuki, M.; Saegusa, T. Polym. B u l l . 1981, 4, 315. Kobayashi, S.; Suzuki, M.; Saegusa, T. Polym. B u l l . 1982, 8, 417. Kobayashi, S.; Suzuki, M.; Saegusa, T. Macromolecules 1983, 16, 1010. Kobayashi, S.; Suzuki, M.; Saegusa, T. Macromolecules 1984, 17,107. Kobayashi, S.; Morikawa, K.; Saegusa, T. Macromolecules, 1975, 8, 386. Kobayashi, S.; Tsuchida, N.; Morikawa, K.; Saegusa, T. Macromolecules 1975, 8, 942. Kobayashi, S.; Morikawa K. Shimizu N. Saegusa T Polym B u l l . 1984, 11, 253 Dahl, B. M.; Dahl Kobayashi, S.; Mizutani, T.; Tanabe, T.; Shimoyama, T.; Saegusa, T. Polym. Prepr. Jpn. 1983, 32, 1475. Kobayashi, S.; Mizutani, T.; Tanabe, T.; Saegusa, T. Polym. Prepr. Jpn. 1983, 32, 230. Kobayashi, S.; Shimoyama, T.; Saegusa, T. Polym. Prepr. Jpn. 1984, 33, 197. Kobayashi, S.; Kobunshi 1984, 33, 228. Webster, O. W.; Hertler, W. R.; Sogah, D. Y.; Farnham, W. B.; RajanBabu, T. V. J . Am. Chem. Soc. 1983, 105, 5706. Kobayashi, S.; Suzuki, M.; Saegusa, T. to be reported. Kobayashi, S.; Suzuki, M.; Saegusa, T. Polym. Prepr. Jpn. 1983, 32, 1399. Kobayashi, S.; Tokunoh, M.; Saegusa, T. Polym. Bull. to be published. Kobayashi, S.; Huang, M. Y.; Saegusa, T. Polym. B u l l . 1981, 4, 185.

RECEIVED February 1, 1985

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23 Synthesis and Polymerization of Atom-Bridged Bicyclic Acetals and Ortho Esters A Dioxacarbenium Ion Mechanism for Ortho Ester Polymerization 1

ANNE BUYLE PADIAS, RYSZARD SZYMANSKI , and H. K. HALL JR. Department of Chemistry, University of Arizona, Tucson, AZ 85721 A review of the synthesis and polymerization of b i c y c l i c acetals and orthoesters i s presented, and the relationship betwee polymerize is discussed acetals and orthoesters were synthesized at high tem perature i n d i o c t y l phthalate under vacuum in order to remove the monomers as soon as they form. The a b i l i t y of the b i c y c l i c monomers to polymerize f a l l s i n the same sequence as the ring s t r a i n : [2.2.1] > [2.2.2] > [3.2.1] > [3.3.1]. The structure of the polymers is determined by two factors: f i r s t , which bond is pre­ f e r e n t i a l l y cleaved, and second, if the reaction i s s t e r e o s p e c i f i c or not. The first factor is determined by Deslongchamps' theory and by the n u c l e o p h i l i c i t y of the ring oxygens. For the least strained b i c y c l i c acetals, the S 2 mechanism leads to s t e r e o s p e c i f i c polymer. The [2.2.1] acetals and the orthoesters, except [2.2.2] and [3.3.1], y i e l d random polymer. An A 2 mechanism, bimolecular addition on a carbenium ion, i s supported i n which the carbenium ion, and not the b i c y c l i c oxonium ion, i s the growing center. The s t e r e o s p e c i f i c i t y observed i n a few cases i s explained by dipole-dipole interaction of chain oxygens with the growing carbenium ion. N

C

This review summarizes a l l the data we obtained on the synthesis and c a t i o n i c ring-opening polymerization of b i c y c l i c acetals and orthoesters, and discusses the relationship between r i n g - s t r a i n and poly­ m e r i z a b i l i t y . This t i e s i n with e a r l i e r work on the polymerizabil­ i t y of monocyclic and b i c y c l i c lactams (1-2)· A new mechanism f o r the propagation step i n the polymerization of b i c y c l i c orthoesters i s supported. 1

Current address: Center of Molecular and Macromolecular Studies, Polish Academy of Sciences, 90-362 Lodz, Poland 0097-6156/ 85/ 0286-0313506.25/ 0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

314

RING-OPENING POLYMERIZATION

B i c y c l l c Acetals: Synthesis The polymerization of unsubstituted b i c y c l i c acetals promised to be a very good f i e l d to study the r e l a t i o n s h i p between ring s t r a i n and polymerizability. In 1973, when we published the f i r s t paper i n t h i s series, Schuerch had already described the polymerization of substituted 1,6-anhydro-aldohexoses to high molecular weight c r y s t a l l i n e polymers (3^)· H a l l and Steuck described the synthesis of one of the least strained members of the acetal s e r i e s , namely, 6,8-dioxabicyclo[3.2.1 ]octane (4)· Kops i n Denmark (5) and Sumitomo In Japan (6_) independently described t h e i r work on this monomer at the same time, and discussed both the synthesis and the polymerization. This b i c y c l i c acetal was synthesized by conventional methods of a c i d i c ring-closure of the c y c l i c alcohol.

OCH.

2,6-Dioxabicyclo[2.2.2]octane i s a more strained system and a s l i g h t l y unusual synthesis was used. The d i o l acetal was treated under a c i d i c conditions to obtain r i n g closure (7). HOCH

^OCH.

2

CHCH CH CH 2

HOCH^

2

N

OCH

The bicyclo[2.2.1Jheptane acetals are much more strained systems. More vigorous conditions are required t o obtain r i n g c l o ­ sure. At the same time these acetals are much more l a b i l e and e a s i l y undergo premature oligomerization. To circumvent this ther­ mal polymerization, the d i o c t y l phthalate synthesis method was devised. These syntheses i n DOP occur i n two steps. The precursor i s dissolved i n d i o c t y l phthalate and heated i n the presence of a trace of acid catalyst. At atmospheric pressure the f i r s t equiva­ lent of alcohol formed i s d i s t i l l e d o f f , r e s u l t i n g i n a monocyclic structure. Higher temperatures are required i n the second step, which results i n the l a b i l e b i c y c l i c compound. A vacuum i s applied to the system i n t h i s second step, and the desired b i c y c l i c acetal w i l l d i s t i l l out of the system as i t i s formed and can be collected i n a cold trap. 2,6-Dioxabicyclo[2.2.1]heptane i s prepared from the d i o l a c e t a l using the DOP method HOCH.

HOCH;

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Atom-Bridged Bicyclic Acetals and Ortho Esters

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315

2,7-Dioxabicyclo[2.2.1Jheptane i s also synthesized using the DOP method, s t a r t i n g from the appropriate d i o l acetal, or more e f f e c t i v e l y , s t a r t i n g from a c r o l e i n and methyl v i n y l ether (8.-9.)·

Acid Hydrolysis of B i c y c l i c Acetals The r e a c t i v i t y of the b i c y c l i c acetals was appraised by means of acid-catalyzed hydrolysis, and was compared to the r e a c t i v i t y of a c y c l i c acetals (8.-9)· The studies were carried out by following the disappearance of the bridgehead a c e t a l proton i n the NMR spectrum (Table I ) .

Table I. Hydrolysis rates of acetals (dichloroacetic acid as c a t a l y s t )

Acetal

relative reactivity

- 1

(sec )

1

dimethyl acetal ΙΟ

7.7

- 5

[3.2.1]

6 χ

[2.2.2]

1.8 χ

ΙΟ"

4

2.5 χ

2,7-[2.2.1]

1.8 χ

ΙΟ"

3

2.5 χ 10*

2,6-[2.2.1]

5.3 χ

ΙΟ"

3

6.9 χ

10

10

3

5

The difference i n hydrolysis rates i s remarkable and can be broadly correlated with the ring s t r a i n : [2.2.1] > [2.2.2] > [3.2.1]. Another s t r i k i n g feature i s the demonstration of marked general acid catalysis i n these systems. Such c a t a l y s i s i s rare f o r ace­ t a l s , however, i t may be encountered where s t e r i c s t r a i n i s relieved i n the rate-determining step, as i n these cases (10).

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RING-OPENING POLYMERIZATION

Polymerization of B i c y c l i c Acetals Reactivity* Q u a l i t a t i v e l y , the order of r e a c t i v i t y i s the same as found f o r the hydrolysis rates: [3.2.1loctane < [2.2.2]octane < 2.7- [2·2.1]heptane < 2,6-[2.2.1Jheptane. This order was determined by comparing the strength of the i n i t i a t o r needed, temperature, time and y i e l d , etc. 6.8- dioxabicyclo[3.2.1]octane: only P F 5 i n dichloromethane at -78°C i s an e f f e c t i v e i n i t i a t o r (4). 2.6- dioxabicyclo[2.2.2]octane: P F 5 and fluorosulfonic acid at -78°C are the most e f f e c t i v e i n i t i a t o r s ; protonlc acids such as methanesulfonic acid and t r i f l u o r o a c e t i c acid are also e f f e c t i v e at room temperature (7_). 2.7- dioxabicyclo[2.2.1]heptane: P F 5 at -78°C i s the best but only low molecular weight polymer i s obtained; also methanesulfonic acid and methyl t r i f l a t e at room temperature (9). 2,6-dioxabicyclo[2.2.1]heptane at -78°C, p a r t i a l ge acid results i n quantitative y i e l d at room temperature (9.)· Polymer Structure. The structure of the acetal polymers has been determined by NMR spectroscopy. The conformational equilibrium f o r both c i s and trans isomers of the dioxabicyclo[3.2.1]- and [2.2.2] octane polymers was calculated by the interplay of two factors: 1) the f a m i l i a r preference of a l k y l substitutents to be i n the equatorial position, and 2) the preference of the alkoxy groups to be i n the a x i a l position, due to the anoraeric e f f e c t . For the polymer of 6,8-dioxabicyclo[3.2.1]octane, only one ace­ t a l proton i s observed ( i t i s equatorial), indicating pure trans1,3-tetrahydropyranoside polymer. Runs at higher temperature show some absorption f o r the c i s isomer.

For the polymer of 2,6-dioxabicyclo[2.2.2]octane, the s i t u a t i o n i s not so clear, because i n this system neither the trans- nor the c i s - l , 4 - u n i t s would be conformationally homogeneous. The observed r a t i o of a x i a l and equatorial protons of the polymers formed at -78°C though are i n very good agreement with the calculated values for the trans isomer. It can thus be concluded that these polymers are also pure trans-l,4-tetrahydropyranoside units. At higher tem­ peratures, more and more cis-linkages are observed.

Examination by NMR of the polymers obtained from 2,7-dioxabicyclo[2.2.1]heptane at -78°C, showed that the polymer was exclusively composed of tetrahydrofuran structures. Cis and trans Isomers are

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Atom-Bridged Bicyclic Acetals and Ortho Esters

randomly distributed. Although the reaction i s not stereospecific, very s p e c i f i c bond cleavage of the C 1 - O 2 bond i s observed.

cis/trans

At higher temperatures the tetrahydrofuran link was s t i l l favored, although several i n i t i a t o r s gave s i g n i f i c a n t amounts of tetrahydropyran l i n k s . The structure of the polymer obtained from ring-opening of 2.6dioxabicyclo[2.2.1Jheptane was examined by NMR, both proton and C. A mixture of c i s and trans isomers of 2,4-tetrahydrofuran l i n k s i s observed. 13

cis/trans

Mechanism. Two mechanistic aspects determine the polymer structure: f i r s t , which bond cleaves? and secondly, i s the reaction stereospecific? The polymer obtained from 6,8-dioxabicyclo[3.2.1]octane only contains tetrahydropyran rings, while the polymer obtained from 2,7-dioxabicyclo[2.2.1Jheptane at low temperature only contains tetrahydrofuran rings. Very s p e c i f i c bond-cleavage occurs i n both these cases. The other two b i c y c l i c acetals can only result i n one polymer structure, due to the symmetry of the monomers. The stereoselective cleavage of a bond i n the oxonium ion may be Interpreted by the approach used by Deslongcharaps (11-12). Specific cleavage of a carbon-oxygen bond occurs when two heteroatoras of the tetrahedral intermediate each have one non-bonded electron pair oriented antiperiplanar to the departing O-alkyl group. In the b i c y c l i c acetals there i s only one heteroatom present, thus the s i t u a t i o n i s not complete, but one p - o r b i t a l i s nicely a n t i p e r i p l a ­ nar (shaded) to the bond to be cleaved. There i s another report i n the l i t e r a t u r e that i n order to obtain s p e c i f i c cleavage of a bond i t Is enough that one p - o r b i t a l i s oriented antiperiplanar to the departing group (13). Another factor i n favor of this bond cleavage i s that the oxygen atoms i n the larger bridges are s l i g h t l y more nucleophilic.

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RING-OPENING POLYMERIZATION

The cationic ring-opening polymerizations of 6,8-dioxabicyclo[3·2.1]octane and 2,6-dioxabicyclo[2.2.2]octane are highly stereoregular at low temperatures and result In pure trans linkages i n the polymer. This implies an S 2 mechanism v i a b i c y c l i c oxonium ions. 0 N

Neither [2.2.1]heptane a c e t a l polymerizes to stereoregular polymer. Another mechanism must be postulated i n this case, and i t can be presented as follows:

The incoming monomer can attack the oxacarbenium ion from either side, resulting i n a random polymer. A s i m i l a r mechanism v i a an oxacarbenium ion was recently pro­ posed i n the cationic ring-opening polymerization of 1,4-anhydro2.3- di-O-benzyl-a-D-xylopyranose by Uryu and Matsuzaki (14). If boron t r i f l u o r i d e etherate, s i l i c o n t e t r a f l u o r i d e or phosphorus pentafluorlde are used as i n i t i a t o r , the authors obtained stereoregular polymer from this substituted b i c y c l i c acetal. If the bulky i n i ­ t i a t o r antimony pentachlorlde i s used, a mixture of a- and β-linked furanose units i s obtained i n the polymer chain. This mechanism v i a an oxacarbenium ion i s an S^l mechanism, i f the raonomolecular cleavage of the b i c y c l i c oxonium ion i s the ratedetermining step. A variant of this mechanism w i l l be discussed l a t e r i n the case of the polymerization of b i c y c l i c orthoesters. B i c y c l i c Orthoesters:

Synthesis

There are several reports i n the l i t e r a t u r e on the synthesis of b i c y c l i c orthoesters. Crank and Eastwood reported the synthesis of the [3.2.1], [3.3.1] and [4.2.1] derivatives, and also noted that these became viscous and turned to glass at room temperature (15). Bailey reported the synthesis of more strained systems, namely, 1.4-diethyl and 4-ethyl-2,6,7-trioxabicyclo[2.2.2]octane (16). Most b i c y c l i c orthoesters we synthesized were obtained from the corresponding t r i o l and trimethyl or t r i e t h y l orthoforraate. Again i t was c r u c i a l that the very sensitive monomers were removed from the reaction mixture as formed. The reactions were run i n d i o c t y l phthalate i n the presence of a trace of p-toluenesulfonic acid as c a t a l y s t . The closure of the f i r s t ring was performed at atmospheric pressure u n t i l two equivalents of alcohol were c o l l e c t e d . The system was then evacuated and heated while con­ tinuing very vigorous s t i r r i n g . The formed b i c y c l i c compounds are then collected i n a dry ice cooled trap or, i n a modified method, as a s o l i d i n a large sublimation apparatus.

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23. PADIAS ET AL.

Atom-Bridged Bicyclic Acetals and Ortho Esters

319

The following unsubstituted b i c y c l i c orthoesters were thus synthesized (17-19):

[3.3.1]

[3.2.1]

[2.2.2]

[2.2.1]

These reactions prove the generality of the DOP method, and this method can probably be extended to the synthesis of other highly strained systems. The same method was also used f o r the synthesis of a whole series of substituted b i c y c l i c orthoesters. Numerous orthoformates and orthoacetates were synthesized with d i f f e r e n t groups i n th

R» = a l k y l , CH Br, CH OH, N 0 , NH , NMe , NHCOCH3, COOMe, 2

2

2

2

2

CH OS0 C7H7-p 2

2

The a l k y l , broraomethyl, hydroxymethyl, n i t r o and dimethylarainosubs tituted b i c y c l i c orthoformates and orthoacetates were synthe­ sized by the interchange reaction of the a c y c l i c t r i o l and a c y c l i c orthoester. The other orthoesters were obtained by d e r i v a t i z a t i o n of the former. To obtain c a t i o n i c water-soluble polyorthoesters, we also synthesized two b i c y c l i c orthoesters containing an ammonium s a l t subs t i tuent. 4-Trime thylammonio-2,6,7-trioxabicyclo[2.2.2]octane trifluorometbanesulfonate was obtained by direct a l k y l a t i o n of the corresponding dimethylamino b i c y c l i c orthoester with methyl trifluoromethanesulfonate ( 2 0 ) .lNMe

0

O S

01NV

°2

C F

3

MeOS0 CF. 9



2,6,7-Trioxabicyclo[2.2.2]octane-4-methylene-N-pyridiniura t r i f l u o r o ­ methanesulfonate was obtained by reaction of the 4-hydroxymethyl derivative with trifluoromethanesulfonic anhydride i n pyridine solu­ tion ( 2 0 ) .

(CF S0 0) 0 2

Py

2

2

r i d i n e

^

'

'

'

OS0 CF

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

2

3

RING-OPENING POLYMERIZATION

320

Hydrolysis of B i c y c l i c Orthoesters* As seen e a r l i e r , the b i c y c l i c acetals are markedly more reactive towards acid hydrolysis than t h e i r a c y c l i c counterparts. These rate accelerations have been attributed to p a r t i a l r e l i e f of the ring s t r a i n upon ring opening hydrolysis. The hydrolysis rates f o r several b i c y c l i c orthoesters have been measured using a c e t i c acid as catalyst, and compared to the hydroly­ s i s rates of a c y c l i c orthoformates (17).

Table I I .

Hydrolysis rates of b i c y c l i c orthoesters

Orthoester

CH(OCH ) 3

10* χ k i (sec

5

)

19

3

CH(OC2H )

- 1

3

[2.2.1]

10

[3.3.1]

4.3

[3.2.1]

4.1

[4.2.1]

3.2

These unexpected results were at the time attributed to a very early t r a n s i t i o n state, with very l i t t l e C-0 bond breaking and consequent­ ly very l i t t l e s t r a i n release. Another explanation was suggested during a more detailed study of the hydrolysis of the [2.2.1] system (21). A change i n the ratedetermining step may be responsible f o r the unusual r e s u l t s . Recent studies of orthoester hydrolysis i n which the f i r s t step of this reaction i s rate-determining, changes to one i n which the t h i r d step i s slower by making s t r u c t u r a l changes that accelerate the rate of the f i r s t step, or by a change i n pH. OR / R-C-OR \ OR

+

HA

OR

//

R-CÎ+

\\

OR // R-Ci + W OR

>

R-C-OR

o

\

OR

OH R-C-OR

HA

+

+ H

/

H0 _ 2

HOR

+ A

OH

^ +

+

il

OR

R-C-OR

+

HOR

\ OR

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23.

PADIAS ET AL.

Atom-Bridged Bicyclic Acetals and Ortho Esters

321

Introduction of s t r a i n , as i n a b i c y c l i c system, i s just such a s t r u c t u r a l change, and the measured rate constant might have been the one for the slower t h i r d step. As such, the acceleration due to the ring s t r a i n of the f i r s t step would be masked by the slower t h i r d step. Such an effect was indeed observed, but the i n i t i a l r i n g opening reaction proved to be not markedly faster than the corresponding reactions of monocyclic and a c y c l i c models. Thus, the theory of an early t r a n s i t i o n state s t i l l stands. Polymerization of B i c y c l i c Orthoesters Reactivity. The r e a c t i v i t i e s of the b i c y c l i c orthoesters can be compared by examining the conditions necessary to form polymer. Although the h y d r o l y t i c r e a c t i v i t i e s were not accelerated, these monomers were indeed very reactive i n polymerization. In contrast to the behavior of the between the hydrolytic c a t i o n i c i n i t i a t o r s f o r the b i c y c l i c orthoesters. The following order can be proposed: [2.2.1] > [2.2.2] > [3.2.1] > [3.3.1] which i s the expected order from the ring strains (18-19). Polymer structure - k i n e t i c control. The structure of the polymer of 2,6,7-trioxabicyclo[2.2.1]heptane i s dependent on the i n i t i a t o r at -78 C i n dichloromethane (18). The polymer i s mostly f i v e membered rings. As i n the b i c y c l i c acetals, i n controlled con­ d i t i o n s , only C 1 - O 2 bond cleavage occurs. e

Contrary to an e a r l i e r report, the polymer obtained from the b i c y c l i c orthoacetate i s also composed of five-merabered rings, as deduced from C NMR spectra (22). 13

0

CH

3

The polymer obtained from 2,6,7-trioxabicyclo[2.2.2]octane i s obviously composed of six-membered rings (19). A l l the polymerizable substituted b i c y c l i c [2.2.2]orthoesters also form the dioxane polymers. With the exception of 4-carbomethoxy-2,6,7-trioxabicyclo [2.2.2]octane, these are highly c r y s t a l l i n e white powders with very high melting points with decomposition, and are not soluble i n any

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RING-OPENING POLYMERISATION

322

solvent without decomposition* In contrast with the polymers obtained by Bailey, which w i l l be discussed l a t e r , these polymers do not show carbonyl stretching i n the infrared spectrum, proving that only one ring opens* H and 13 NMR spectra of low molecular weight polymer of unsubstituted 2,6,7-trioxabicyclo[2*2.2]octane show only one s i g n a l f o r the orthoester proton and carbon. These results suggest that the stereoregularity of this polymer i s extremely high, probably trans. The polymer obtained from 2,7,8-trioxabicyclo[3.2.1]octane con­ s i s t s mostly of five-membered rings (23). Six- and seven-membered rings are also observed, but only for about 15%. These polymers were analyzed by *H NMR and by comparison of these spectra with model compounds. The r a t i o of c i s and trans i s always about .50/50. No s t e r e o s e l e c t i v i t y i s observed, although the presence of mainly five-membered rings indicates a great preference to cleave the C 1 - O 2 bond. A

C

2,7,8-Trioxabicyclo[3.3.1Jnonane leads to dimers and oligomers under the influence of most c a t i o n i c I n i t i a t o r s (23). But when trifluoromethanesulfonic acid i s used as i n i t i a t o r i n dichloromethane at -78°C, only dlmer i s formed. Only one orthoformate pro­ ton Is observed i n the NMR spectrum, which indicates that only one conformation and configuration of monomer units occurs i n the dimer. Water-soluble polymers. Substituted water-soluble poly-orthoesters can be regarded as polysaccharide analogs, and could have p o t e n t i a l medical applications as drugs or as drug c a r r i e r s . Ionic s u b s t i ­ tuents were introduced In the b i c y c l i c monomers to improve the s o l u ­ b i l i t y of these polymers. The two b i c y c l i c orthoesters with the trimethylammonio- and the pyridinium-methylene-substituents i n the 4-position did not poly­ merize well under the influence of c a t i o n i c i n i t i a t o r s , as could be expected. However, high molecular weight poly-orthoester could be obtained by copolymerizing the former with 2,6,7-trioxabicyclo[2.2.1]heptane (20). The copolymer i s soluble i n water and i n orga­ n i c solvents.

In order to obtain an anionic poly-orthoester, 4-carbomethoxy-2,6,7trioxabicyclo[2.2.2]octane was polymerized using trifluoromethane­ sulf onic acid as i n i t i a t o r i n dichlororaethane at -78°C (20). This i s the only known poly-orthoester i n the [2.2.2]-series that i s

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23.

PADIAS ET AL.

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Atom-Bridged Bicyclic Acetals and Ortho Esters

X

soluble i n organic solvents. Also, both H and NMR spectra indicated that approximately equal amounts of two isomers are pre­ sent, i n contrast with a l l the other polymers i n this series which were stereoregular. This polymer was then hydrolyzed i n aqueous pyridine/potassium hydroxide, and the products were separated by d i a l y s i s . Only a 50% y i e l d of hydrolyzed product i s obtained, but t h i s i s the f i r s t report of a water-soluble poly-orthoester with anionic substituents on the polymer chain. C 0 0 C H

°l lX^^ ζΧ^Ί

3

CH OOC

>—

3

K K

0

~-0CH \_ >~ 2

P^

0

I

D

I

N

E

'

+

"ooc ooc

0

^ C H ^ < /

Polymer structure-thermodynamlc c o n t r o l . The polymers described above, containing dloxolane and dioxane rings, are the k i n e t i c a l l y controlled products i n polymerization of severa orthoesters under much harsher conditions (24), Simultaneous opening of both rings i s achieved i n t h i s way, leading to l i n e a r polyethers with ester branching. This i s usually accompanied by volume expansion. We thoroughly investigated the polymerization of 2,6,7-trioxabicyclo[2.2.1Jheptane under d i f f e r e n t conditions (25). At low tem­ perature (-78°C) only one ring opened, but at higher temperatures (80°C) polyethers with formate side chains are obtained. The opening of the second r i n g was also observed i n dioxolane polymers, l e f t at room temperature f o r several days or heated to 80°C f o r a few hours. The dioxolane-containing polymer was stable i f the acid c a t a l y s t was neutralized.

- 4 0 C H -CH-0—) 0

2

J 'n CH 0CH0 2

(-0CH -CH-CH 0—) o

o

2 J 2 OCHO

'm

The same phenomenon was observed i n the polymerization of the [2.2.2]orthoesters: polymers with ester-branching are formed under vigorous conditions, by isomerization of the k i n e t i c a l l y controlled polymers under acid c a t a l y s i s (19). More recently, Matyjaszewski aleο described the same phenomenon i n the polymerization of a s p i r o orthoester, l,4,6-trioxaspiro[4.4]nonane (26). Mechanism; Selective bond cleavage. Cationic polymerization of 2,6,7-trioxabicyclo[2.2.1]heptane y i e l d s a polymer consisting of

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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RING-OPENING POLYMERIZATION

almost exclusively five-membered rings, indicating that cleavage of the C 1 - O 2 / 6 bond i s preferred (18). Thermodynamically the s i x membered ring i s more stable than the five-membered rings obtained i n these polymers* The polymer formation i s k i n e t i c a l l y controlled.

0

0

R The s e l e c t i v e cleavage of a s p e c i f i c bond i n the oxonium i o n i s interpreted as follows: 1) O2 and 0$ have higher p-character than O 7 , because t h e i r bond angles are close to 100° and 90°, respec­ t i v e l y . Accordingly, O2 and 0$ are more nucleophilic. 2 ) The stereoselective contro l i n e s of Deslongchamps t a l s . Here though, always two p-orbitals (shaded) w i l l be a n t i periplanar to the bond to be cleaved.

Q 0

0

The same phenomenon i s observed i n the polymerization of 2,7,8trioxabicyclo[3.2.1]octane (23). The five-membered rings are domi­ nant i n the polymer chain, although some s i x - and seven-membered ringβ are also observed. The preferred C 1 - O 2 bond cleavage can be ascribed to Deslongchamps' theory, which i s v a l i d f o r two oxygen atoms In the monomer, and to the higher p-character of the oxygen at the 2-position. This oxygen i s on the longest bridge and thus less strained than the others. A dioxacarbenium i o n mechanism f o r b i c y c l i c orthoesters. The equilibrium between carbenium ions and oxonium ions i n the c a t i o n i c polymerization of monomers containing heteroatoms has been discussed i n the l i t e r a t u r e , s p e c i f i c a l l y i n the case of c y c l i c ethers and acetals (27-29). In analogy, the growing center i n the polymeriza­ t i o n of b i c y c l i c orthoesters can be either a b i c y c l i c oxonium i o n or a dioxacarbenium ion. In this reaction sequence either step can be 0

rate-determining. If the f i r s t step i s f a s t , then the monoraolecular r i n g opening of the b i c y c l i c oxonium i o n i s rate-determining and the

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23. PADIAS ET AL.

Atom-Bridged Bicyclic Acetals and Ortho Esters

325

mechanism Is a c l a s s i c a l Sjjl, which was proposed when t h i s work was f i r s t published (18). If the attack of monomer on the dioxacarbenlum ion i s rate-determining, then most of the growing centers w i l l be carbenium ions. The non-stereospecificity of the polymeri­ zation i n either case i s due to attack of monomer on either side of the planar dloxacarbenlum ion. In the polymerization of monocyclic ethers and acetals discussed by Penczek (27), the carbenium ions are primary, with one adjacent oxygen i n the l a t t e r case, and propaga­ t i o n occurs through the more stable oxonium ions. The obvious s t a ­ b i l i z a t i o n of the c y c l i c dloxacarbenlum ions by the two adjacent oxygens made us reexamine this reaction. F i r s t , k i n e t i c studies of the polymerization of 2,6,7-trioxabicyclo[2.2.1]heptane were attempted. 1,3-Dioxolan-2-ylium s a l t was chosen as i n i t i a t o r , because of the s i m i l a r i t y of the i n i t i a t i o n reaction i n this case to the propagation reaction.

kjskp, where k^ and k constants.

p

are the i n i t i a t i o n and propagation rate

Preliminary experiments indicated that the propagation rate constant i s too high to be measured by conventional methods. Even when the i n i t i a t o r concentration was as low as 1.1 χ 10" 7 M i n nitromethane-d3, the propagation reaction was f i n i s h e d before an NMR spectrum could be recorded to check the monomer/polymer r a t i o . Inasmuch as a f t e r 5 minutes of reaction [M ]/[M]>30 f o r [ I ] » 1.1 χ 10~7 M, the propagation rate constant was estimated to be higher than 1 χ 10 M"^s at room temperature. This lower l i m i t of the propagation rate constant suggests that dloxolanylium cations, and not oxonium ions, are the active species. The rate constants f o r combination of various carbenium ions with neutral nucleophiles are reported to be greater than 10 H" s" (28,30-31). For example, the rate constant of the reaction of methoxymethylium cation with methyl ether i n s u l f u r dioxide i s about 5 χ 10° M" s" at 30° (28). The rate constant of the reaction of 1,3-dioxolan-2-ylium cation with oxygen nucleophiles i s expected to be about one order of magnitude lower due to the s t a b i l i z a t i o n provided by the two oxygen atoms. Second, the oxonium ion-carbenium ion equilibrium i n the orthoester systems was investigated. A model compound f o r the active center was synthesized. 4-Methoxymethyl-l,3-dioxolan-2-ylium cation i s the model compound f o r the carbenium ion i n the polymeri­ zation of 2,6,7-trioxabicyclo[2.2.1]heptane, and was obtained by hydride transfer from 4-methoxymethy1-1,3-dioxolane to t r i p h e n y l methylium cation. o

5

0

-1

6

1

1

1

1

SbF,

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326

RING-OPENING POLYMERIZATION

The *H NMR spectra of the reaction mixture confirm that i n t e r molecular (with unreacted acetal) as well as interraolecular carbenium-oxonium ion e q u i l i b r i a are shifted f a r toward the car­ benium cation i n nitromethane-d3 at room temperature* No evidence for oxonium ion formation was found.

Unfortunately, the syste perature because of p r e c i p i t a t i o 5-Methoxymethyl-5-methyl-l,3-dioxane was b r i e f l y investigated as an example f o r a less strained system and the precursor of the model compound f o r the growing cation i n the polymerization of 2,6,7trioxabicyclo[2.2.2]octane. Hydride transfer to triphenylmethylium cation i s so slow and the r e s u l t i n g 1,3-dioxan-2-ylium cation i s so unstable that a considerable amount of side products i s formed before half of the dioxane has reacted* But even i n these rough experiments the concentration of carbenium Ion c l e a r l y exceeds the concentration of oxonium ions.

Third, the reaction of l,3-dioxolan-2-ylium cation with mono­ c y c l i c orthoesters was investigated. A c a t a l y t i c amount of 1,3-dioxolan-2-ylium cation brought about the exchange between 2-methoxy- and 2-ethoxy-l,3-dioxolane.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23. PADIAS ET AL.

327

Atom-Bridged Bicyclic Acetals and Ortho Esters

This exchange i s due to combination of the l,3-dioxolan-2-ylium cation with 2-alkoxy-l,3-dioxolane, which leads to an unstable sym­ metric oxonium cation.

This exchange i s the model reaction f o r the attack of monomer on the dioxacarbenium ion i n the propagation step. The combination rate constant k was derived from the exchange rate constant which was measured by dynamic *H NMR l i n e shape analy­ s i s . The combination rate constant i s about 3 χ 10* M^s"" at 20° with a low enthalpy of activation, about 2 kcal/mole (see Experimen­ t a l f o r more d e t a i l s ) . Th 1,3-dioxolane system catalyze gests the s i m i l a r i t y of this process to the cationic polymerization of the orthoesters, and that the active species i n both processes have the l,3-dioxolan-2-ylium structure rather than the oxonium structure. The fact that the lower l i m i t f o r the propagation rate constant i s higher than the rate constant f o r the model reaction can be explained by s t e r i c and s t a t i s t i c a l f a c t o r s . The monomer has two nucleophilic centers which are less s t e r i c a l l y hindered than the one alkoxy oxygen atom i n the 2-alkoxy-l,3-dioxolanes. Taking a l l these data into account, the following Aç2 mechanism (bimolecular addition on a carbenium ion) i s supported for the poly­ merization of the [2.2.1Jbicyclic orthoester. It presumably i s v a l i d f o r a l l b i c y c l i c orthoesters, at least at room temperature or higher temperatures. 0 c

1

In t h i s mechanism the rate-determining step i s the bimolecular reac­ t i o n of the c y c l i c dioxacarbenium ion with monomer. The Aç2 mecha­ nism also predicts the non-stereospecificity of the propagation step. The polymer obtained from 2,7,8-trioxabicyclo[3.2.1]octane i s not stereospecific, and as such the Aç2 mechanism can also be pro­ posed i n this case. High s t e r e o s e l e c t i v i t y i s observed i n the unsubstituted 2,6,7trloxabicyclo[2.2.2]octane polymerization. In analogy to the [2.2.1] case, the AQ2 mechanism i s also proposed In t h i s case. The high s t e r e o s e l e c t i v i t y i s due to weak dipole-dipole interactions

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

328

RING-OPENING POLYMERIZATION

between the dioxacarbenium i o n and the f i r s t oxygen i n the chain, which i s i n perfect position to shield one side of the dioxacar­ benium i o n (19). /

The fact that the [3.3.1] b i c y c l i c orthoester does polymerize, i s rather surprising, because i t consists of two fused six-membered rings i n the chair form. A small but s i g n i f i c a n t ring s t r a i n i s due to the repulsion between the two endo-protons at C3 and C7. The formation of only one isome weak dipole-dipole interaction the f i r s t chain oxygen which force the incoming monomer to react In a stereoselective fashion. The formation of the dimer can then be interpreted i n terms of back-biting of the growing chain end (23). From these r e s u l t s , the Aç2 mechanism can also be proposed i n t h i s oligomerization.

Ψ

Conclusion In conclusion, we can state that ring s t r a i n does play an important role i n determining the polymerizability of b i c y c l i c acetals and orthoesters. The sequence i s as follows: [2.2.1] > [2.2.2] > [3.2.1] > [3.3.1]. The r i n g s t r a i n i s affected by the r i n g s i z e , the gauche interactions i n the monomer, the conformation i n the

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23.

PADIAS ET AL.

Atom-Bridged Bicyclic Acetals and Ortho Esters

329

monomer, and the anomeric e f f e c t , as discussed by Yokoyama and H a l l i n a recent review (32). This sequence i s general for a l l b i c y c l i c compounds, independently of the f u n c t i o n a l i t i e s . It i s v a l i d f o r the b i c y c l i c acetals and orthoesters as described i n this review, f o r the b i c y c l i c lactams and lactones, b i c y c l i c oxalactones and oxalactams (33), etc. The preferred bond cleavage i n the polymerization of these b i c y c l i c acetals and orthoesters i s determined by Deslongcharaps' theory. If a l l oxygens are equally preferred by the former, the pcharacter of the oxygen atom, determined by the bond angles, w i l l be the dominant factor. For the least strained b i c y c l i c acetals, the SJJ2 mechanism i s proposed, leading to s t e r e o s p e c i f i c polymer. Polymerization of the [2.2.1] acetals leads to random polymer, and a mechanism v i a an oxacarbenlum ion i s supported. A novel mechanism i s supported for the b i c y c l i c orthoester poly­ merization, namely, an the dloxolanylium cation Experimental of B i c y c l i c Orthoesters Mechanism Studies Instrumental. *H NMR spectra were recorded on 60 MHz Varian EM360L NMR spectrometer and 250 MHz Brucker WM-250 FT spectrometer. C NMR spectrum was recorded on Brucker WH-90 spectrometer. 1 3

So1vent. Nitromethane (Aldrich) was kept i n a vacuum ampoule equipped with a Rotaflo stopcock over calcium hydride. It was d i s t i l l e d into the reaction vessels on a vacuum l i n e . Monomer. 2,6,7-Trioxabicyclo[2.2.1]heptane was prepared by the DOP method (18) and was kept i n a vacuum ampoule (equipped with a Rotaflo stopcock) over a sodium mirror. Samples f o r polymerization were prepared by d i s t i l l a t i o n of the monomer i n a vacuum system to ampoules equipped with breakseals. I n i t i a t o r . l,3-Dioxolan-2-ylium hexafluoroantimonate was prepared and handled as described by Stolarczyk, Kubisa and Penczek (34). Solutions of the s a l t were prepared i n vacuum flasks equipped i n Rotaflo stopcocks. Triphenylmethyl hexafluoroantimonate (Ozark-Mahoning) was p u r i f i e d i n p r e c i p i t a t i o n from dichloromethane solution by hexane. Model Compounds. 4-Methoxyeethyl-l, 3-dioxolane: 3-Metboxy-1,2-pro­ panediol (5.3g) was mixed with 10g of dimetboxymethane and, a f t e r adding a c a t a l y t i c amount of p-toluenesulfonic acid, the mixture was refluxed for 3 hr. Then the reaction mixture was d i s t i l l e d on a Vigreux column. Y i e l d : 0.3g (5%), b.p. 40-50°/20mmHg, *H NMR (CD N0 ), δ: 4.87(s, 1H), 4.73(s, 1H), 4.2-3.3(m, 5H), 3.30(s, 3H) ppm. The main product was dimer: y i e l d : 4.2g (71%), b.p. 68°/5mmHg. S-Hydroxyeethyl-S-methyl-l^-dioxane: A mixture of 20g of 2hydroxymethyl-2-methyl-l,3-propanediol (Aldrich), 5g of trioxane (Matheeon, Coleman and B e l l ) and 1.5mL of concentrated hydrochloric acid was slowly heated to 100° u n t i l the mixture became homogeneous. 3

2

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

330

RING-OPENING POLYMERIZATION

Then most water was d i s t i l l e d o f f at 20mm and the residue f r a c t i o n nated on a Vigreux column. Y i e l d : 15g (68%), b.p. 78°/2mmHg, *H NMR (acetone-d6, δ: 4.6-4.95 (pseudo quartet, J«6Hz, 2H), 3.3-4.0 (pseudo quartet, J*10Hz), 3.70(s), 3.53(s) (combined 7H), 0.85(s, 3H) ppm. 5-Methoxymethyl-5-methyl-l,3-dioxane: 5-Hydroxymethyl-5-methy11,3-dioxane (8g) was dissolved i n 50mL of anhydrous tetrahydrofuran. Then 1.5g of sodium and 4mL of methyl iodide was added. The reac­ t i o n mixture was s t i r r e d overnight at a temperature below 40°. The s o l i d was f i l t e r e d o f f and the f i l t r a t e d i s t i l l e d . Y i e l d : 4.0g (50%), b.p. 52-54°/20mmHg, H NMR (acetone-d6), 6: 4.6-5.0 (pseudo quartet, J«5Hz, 2H), 3.3-4.0 (pseudo quartet, J«llHz), 3.40(s), 3.33(s) (combined 9H), 0.87(s, 3H) ppm. 2-Methoxy-l,3-dioxolane and 2-ethoxy-l,3-dioxolane: Trimethyl orthoformate, or t r i e t h y l orthoformate, was mixed with an equimolar amount of ethylene g l y c o l i n the presence of a trace of p-toluenes u l f o n l c acid. The mixtur then the corresponding were p u r i f i e d by d i s t i l l a t i o n and kept i n a vacuum ampoule over calcium hydride. Έί NMR (CD N0 ), δ: 5.7(s, IH), 4.0(s, 4H), 3.3(s, 3H) ppm. X

ι

3

2

Polymerization k i n e t i c studies. The polymerizations were carried i n completely sealed vacuum vessels which were equipped with two breakseal ampoules, one with the monomer, the other with a solution of i n i t i a t o r . They were also equipped with two NMR tubes. The desired amount of solvent was d i s t i l l e d i n on the vacuum l i n e and the reaction vessel was sealed o f f . The breakseal of the monomer was then broken. After dissolving the monomer, a sample of the s o l u t i o n was sealed o f f i n one NMR tube to make sure that the monomer i s stable i n the solution without i n i t i a t o r . Then the breakseal of i n i t i a t o r solution was broken and the solutions mixed. The NMR tube was f i l l e d and sealed o f f . Immediately *H NMR spectra were recorded. Vacuum l i n e technique. In the past, the polymerizations were run i n vacuum or In a nitrogen or argon atmosphere, and septurns and syringes were used extensively. The present investigation using high vacuum (10"*5 Hg) undertaken to determine i f the low mole­ cular weights and the non-stereospecific nature of the obtained polymers were due to the methods used or to the mechanism. The pre­ sent study c l e a r l y indicates that the use of high vacuum does not improve the s t e r e o s p e c i f i c i t y of the polymer. The molecular weights of the polymer were improved and closer to the expected value c a l c u ­ lated from the monomer/initiâtor value. Also monomer stored over a sodium mirror i n high vacuum conditions was completely stable, proving that the d i f f i c u l t i e s encountered before i n storing the monomer were solely due to adventitious hydrolysis. mm

w

a

s

Hydride transfer reactions. A known amount of triphenylmethyl hexafluoroantlmonate was placed i n an NMR tube attached to a vacuum l i n e . After 30 minutes vacuum drying of the s a l t , the desired amount of nitromethane-d3 model compound was d i s t i l l e d i n and the NMR tube sealed o f f . The reactions were carried out at room temperature and the products were not i s o l a t e d . a

n

d

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23.

PADIAS ET AL.

Atom-Bridged Bicyclic Acetals and Ortho Esters

331

Orthoformate exchange studies. The rate constant for the exchange between 2-methoxy-1,3-dioxolane and 2-ethoxy-l,3-dioxolane brought about by a c a t a l y t i c amount of l,3-dioxolan-2-ylium cation was measured by dynamic H NMR l i n e shape analysis. The following reac­ tions occur i n this system. 1

The dloxolane rings are marked to present the path of the exchange between the two orthoformates. The oxonium ion i s an intermediate i n the exchange reaction, and because of i t s symmetry the exchange rate constant i s equal to k /2 (combination rate constant). If the exchange occurs i n equimolar s o l u t i o n of 2-methoxy- and 2-ethoxy-l,3-dioxolane, the pseudo f i r s t order rate constant of exchange may be expressed as c

k

+

e x

« k [C ] /4 c

0

+

where [ C ] i s the l,3-dioxolan-2-ylium s a l t concentration. This assumption i s correct i f the concentration of oxonium cations i s n e g l i g i b l e , which was proven by NMR. The experiments were prepared i n the same way as described for the polymerization studies on a vacuum l i n e . The dynamic NMR spectra were recorded s t a r t i n g from the lowest temperature. Simula­ tions of the spectra were made using the DNMR 3 program. The exchange rate constant was assumed to be the value which gave the most s i m i l a r simulated spectrum. Such parameters as s i g n a l width and maximum and saddle intensity ratios were compared. Accuracy of determination of exchange rate constant was better than 5%. The results of the l i n e shape analysis study of the orthoformate protons (2-position of the ring) are summarized i n Table I I I . A brief l i n e shape analysis study was also completed on the NMR signals of the 4,4,5,5-ring protons of 2-methoxy-1,3-dioxolane. This i s a much more complicated system. The value of the exchange rate constant was s i m i l a r to the value reported i n Table I I I f o r the orthoformate protons. Q

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332

RING-OPENING POLYMERIZATION

Table I I I . Rates of exchange and calculated rate constants of combination of l,3-dioxolan-2-ylium hexalfuoroantimonate with 2-methoxy-l,3 dioxolane and 2-ethoxy-l,3-dioxolane i n nitromethane-d3«

temperature (°C)

concentration of 1,3-dioxolan-2-ylium s a l t (Μ χ 10 )

25

0

-15

-30

^ex 1

(s" )

(M-lsxlO-*)

1.51

5.7

1.5

3.59

23.5

2.6

1.51

3.5

3.59

10.5

1.2

8.48

45.6

2.1

1.51

3.2

3.59

10.0

1.1

8.48

34.9

1.7

3

1

1

(M-ls" xlO" ) 4

2.4

0.93 1.4

0.83

1.51

2.3

0.62

3.59

9.5

1.1

8.48

21.1

1.0

1.2

0.90

[2-methoxy-l,3-dioxolane] * [2-ethoxy-l,3-dioxolane] » 0.404 M

Acknowledgments The authors are deeply indebted to the National Institutes of Health, GM 18595, f o r support of this work. Literature 1. 2. 3. 4. 5.

Cited

H a l l , H.K., J r . J . Amer. Chem. Soc. 1958, 80, 6404. H a l l , H.K., J r . J . Amer. Chem. Soc. 1958, 80, 6412. Schuerch, C. Acc. Chem. Res. 1973, 6, 184. H a l l , H.K., J r . ; Steuck, M.J. J . Polym. S c i . , Polym. Chem. Ed. 1973, 11, 1035. Kops, J . J . Polym. S c i . A-1 1972, 10, 1275.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

23. PAD1AS ET AL.

6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22.

Atom-Bridged Bicyclic Acetals and Ortho Esters

Sumitomo, H.; Okada, M.; Hibino, Y. J . Polym. S c i . Β 1972, 10, 871. H a l l , H.K., J r . ; Carr, L.J.; Kellman, R.; De Blauwe, F. J . Amer. Chem. Soc. 1974, 96, 7265. H a l l , H.K., J r . ; De Blauwe, F. J . Amer. Chem. Soc. 1975, 97, 655. H a l l , H.K., J r . ; De Blauwe, F.; Carr, L.J.; Rao, V.S.; Reddy, G.S. J. Polym. S c i . , Symp. 1976, 56, 101. F i f e , T.H. Acc. Chem. Res. 1972, 5, 764. Deslongchamps, P. Tetrahedron 1975, 31, 2463. Deslongchamps, P. Heterocycles 1977, 7, 1271. Kirby, A.J.; Martin, R.J.. Chem. Commun. 1978, 803; i b i d . 1979, 1079. Uryu, T.; Yamanouchi, J.; Hayashi, S.; Tamaki, H.; Matsuzaki, K. Macromolecules 1983, 16, 320. Crank, G; Eastwood, F.W. Aust. J . Chem. 1964, 17, 1385. Bailey, W.J.; Endo 17. H a l l , H.K., J r . ; De Blauwe, F.; Pyriadi, T. J . Amer. Chem. Soc. 1975, 97, 3854. Yokoyama, Y.; Padias, A. Buyle; De Blauwe, F.; H a l l , H.K., J r . Macromolecules 1980, 13, 252. Yokoyama, Y.; Padias, A. Buyle; Bratoeff, E.A.; Hall, H.K., J r . Macromolecules 1982, 15, 11. Szymanski, R.; H a l l , H.K., J r . J . Polym. S c i . , Polym. Lett. Ed. 1983, 21, 177. Burt, R.A.; Chiang, Y.; H a l l , H.K., J r . ; Kresge, A.J. J . Amer. Chem. Soc. 1982, 104, 3687. C NMR spectrum of poly-(1-methyl-2,6,7-trioxabicyclo[2.2.1] heptane) i n CDCl : δ = 121.66, 121.53(CO ), 74.55(CH), 66.91(endocyclic CH ), 62.60, 62.25(exocyclic CH ), 21.95(CH ) ppm. Yokoyama, Y.; H a l l , H.K., J r . J . Polym. S c i . , Polym. Chem. Ed. 1980, 18, 3133. Endo, T.; Saigo, K.; Bailey, W.J. J . Polym. S c i . , Polym. L e t t . Ed. 1980, 18, 457, 771. H a l l , H.K., J r . ; Yokoyama, Y. Polym. B u l l . 1980, 2, 281. Matyjaszewski, K. J . Polym. S c i . , Polym. Chem. Ed. 1984, 22, 29. Penczek, S.; Kubisa, P.; Matyjaszewski, K. Adv. Polym. S c i . 1980, 37, 1. Penczek, S.; Szymanski, R. Polymer J. 1980, 12, 617. Szymanski, R.; Penczek, S. Makromol. Chem. 1982, 183, 1587. Slomkowski, S.; Penczek, S. J . Chem. Soc., Perkin Trans. I I 1974, 1718. Penczek, S. Makromol. Chem. 1974, 175, 1217. Yokoyama, Y.; H a l l , H.K., J r . Adv. Polym. S c i . 1982, 42, 107. Sumitomo, H.; Okada, M. Adv. Polym. S c i . 1978, 28, 47. Stolarczyk, Α.; Kubisa, P.; Penczek, S. J . Macromol. Sci.-Chem. 1977, A11, 2047.

13

3

3

2

23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34.

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2

RECEIVED October 4, 1984

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

3

24 Radiation-Induced Cationic Polymerization of Limonene Oxide, α-Pinene Oxide, and β-Pinene Oxide J A M E S A. AIKINS and F F R A N C O N WILLIAMS

1

Department of Chemistry, University of Tennessee, Knoxville, T N 37996-1600

After suitable drying, the subject monomers i n the form of neat liquids undergo radiation-induced poly­ merization with n t sid reaction d high conversions to precipitatabl ular weight. A hig transfer to monomer i s indicated by the fact that the k i n e t i c chain lengths are estimated to be several hundred times larger than the range of DP values (12-4). Structural characterization of the limonene oxide polymer by H and C NMR spectroscopy provides conclusive evidence that the polymerization proceeds by the opening of the epoxide ring to y i e l d a 1,2­ -trans polyether. Similar NMR studies on the polymers formed from the α-pinene and ß-pinene oxides show that the opening of the epoxide ring for these monomers i s generally accompanied by the concomitant ring opening of the cyclobutane ring structure to yield a gem-dimethyl group i n the main chain. n

1

13

The radiation-induced cationic polymerization of vinyl and unsatu­ rated monomers i n the l i q u i d state has been studied for over 25 years, and the essential features of this type of polymerization appear to be well established (1,2)· In contrast to cationic polymer­ i z a t i o n by catalysts where the propagating species i s usually described as a solvated ion pair, the d i s t i n c t i v e c h a r a c t e r i s t i c of cationic polymerization induced by high energy radiation i s that propagation occurs by free ions with very large rate constants, the range of kp values for observable polymerization being from 10 M"" s" to 10 M" s" . Since the concentration of free ions i s t y p i c a l l y about 10" M for dose rates obtainable from k i l o c u r i e Co gamma-radiation sources, the rates of polymerization are very sensi­ tive to traces of impurities, including water (3), that can function as e f f i c i e n t terminating agents. Consequently, much attention has been paid to the development of stringent experimental techniques f o r the rigorous drying of monomers (1H>), since otherwise this type of polymerization may go unrecognized. 1

1

8

1

1

10

7

Author to whom correspondence should be directed.

0097-6156/85/0286-0335$07.25/0 © 1985 American Chemical Society

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RING-OPENING POLYMERIZATION

As compared to vinyl monomers, r e l a t i v e l y few studies of ringopening polymerization induced by high energy radiation have been reported in the l i q u i d state (7). Easily the best documented example is the polymerization of 1,2-cyclohexene oxide described by Cordischi, Mele, and their co-workers (8-10)* These authors found that the polymerization of this epoxide displays many of the charac­ t e r i s t i c s previously observed for the radiation-induced cationic polymerization of unsaturated monomers, including the great s e n s i t i v ­ i t y to water 03) and the strongly retarding effect of ammonia (11). In view of our e a r l i e r work on the polymerization of 3~pinene (12,13), i t seemed of interest to attempt the ring-opening polymer­ ization of the epoxides of limonene UJ , α-pinene [2], and 3-plnene [3J by i r r a d i a t i o n i n the l i q u i d state. We were also encouraged to carry out this study by the report of Ruckel and co-workers (14) on the successful c a t a l y t i c cationic polymerization of these epoxides. In p a r t i c u l a r , these authors obtained evidence for the occurrence of a molecular rearrangemen epoxides of a- and 3-pinene followed with high probability by the concomitant opening of the cyclobutane ring structure in these monomers. This l a t t e r rearrangement i s also known in the cationic polymerization of 3-pinene (L2-16). Experimental The monomers, obtained from Aldrich Chemical Co., were pre-dried for 72 hours over molecular sieves and d i s t i l l e d under reduced pressure immediately before use. Elaborate drying techniques similar to those used in previous studies of isobutylene (5) and vinyl ethers (6) are unsuitable for monomers of low v o l a t i l i t y , and therefore we resorted to a simpler method using a bake-out apparatus of the type o r i g i n a l l y described by Metz and his co-workers (4). This consisted e s s e n t i a l l y of an a l l - g l a s s manifold containing indicator-grade s i l i c a gel as the drying agent (13), the entire apparatus being baked out in an oven at 350°C for 2-3 days under high vacuum before being attached to a conventional vacuum line and charged with monomer. The detailed procedure for the preparation of neat monomer samples in vacuo by this technique followed closely the description given previously for studies of 3-pinene (13). The sample tubes were irradiated for the specified total doses in a Gammacell-200 (Atomic Energy of Canada Ltd.) C o source. Allowing for Co decay, the standard dose rate calibrated by Fricke dosimetry decreased from 0.094 Mrad hr" (August, 1982) to 0.078 Mrad hr" (January, 1984) during the period of this investigation. Although most irradiations were carried out at the ambient tempera­ ture of the Gammacell chamber (ca. 25°C), a few samples were i r r a d i ­ ated in Dewar vessels containing ice (0°C), s o l i d carbon dioxide (-78°C), or l i q u i d nitrogen (-196°C). In order to check the cationic nature of the polymerization mechanism, a few samples were doped with low concentrations (ca. 10" M) of tri-n-propylamine which was introduced d i r e c t l y into the vacuum l i n e . Usually, the last sample in a given batch was treated in this way to avoid contaminating the rest of the material. After γ i r r a d i a t i o n , the sample tubes were opened in a glove bag 60

1

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24.

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337

providing an oxygen-free atmosphere, and the monomer-polymer mixture dissolved in methylene chloride. The polymer was precipitated as a white powder by addition of methanol and collected by f i l t r a t i o n , after which i t was assayed by drying to constant weight i n a vacuum dessicator. To minimize autoxidation, which was especially severe for the polymers from α-pinene oxide and 3-pinene oxide that were l e f t standing i n the atmosphere under ambient conditions, polymer samples intended for storage were reprecipitated with methanol in the presence of an antioxidant ( F l e c t o l H - polymerized 1,2-dihydro2,2,4-triraethyl-quinoline supplied by the Monsanto Chemical Co.) so as to disperse the l a t t e r i n the s o l i d polymer. Molecular weight measurements on the polymers were made using a Knauer vapor pressure osmometer (Utopia Instrument Co.) with pyridine as the solvent at 60°C. Additional measurements with a similar osmometer were made by Galbraith Laboratories, Inc. using chloroform as the solvent at 45°C, the osmometer calibration factor having been obtained with phenacetin NMR and IR spectr tions i n chloroform (CDCI3) and carbon tetrachloride, respectively. The H and C-NMR spectra which are presented in this paper were recorded with a 200 MHz (Nicolet NT 200) instrument while additional H NMR spectra were taken during the course of the work with both 90 MHz (JEOL FX90 Q FT) and 60 MHz (Varian T-60) spectrometers. IR spectra were recorded with a Perkin-Elmer 727 instrument. The thermal properties of the polymers were measured using a Perkin-Elmer d i f f e r e n t i a l scannning calorimeter. 13

Results Kinetic Characteristics of Polymerization (-t-)-Limonene Oxide. Data showing the extent of monomer conversion to polymer as a function of i r r a d i a t i o n dose are presented in Table I. Considering the general problem associated with the great s e n s i t i v i t y of radiation-induced cationic polymerizations to adventitious impuri­ ties and small residual concentrations of water i n the monomer (J-j>), there i s a reasonable degree of reproducibility i n the (ï(-M) values obtained at 25°C from batches I and II, the average value from eight determinations being 2472 with a standard deviation (N • 8 weighting) of 601. Although the only value (G(-M) = 819) from batch III at 25°C is well below this mean, the result at 0°C from this same batch i s lower by a factor of more than two. While these results at 0 and 25°C are i n s u f f i c i e n t to establish the temperature dependence of the polymerization rate i n the f l u i d state, i t i s s i g n i f i c a n t that the polymerization rates at -78 and -196°C are about a factor of 10 to 50 times lower. Since the monomer becomes extremely viscous at -78°C and hardens to a glassy s o l i d at -196°C, the polymerization evidently does not proceed as readily i n the s o l i d state at low temperatures. There i s no evidence from the data in Table I that the polymer­ ization rate, as measured by the £(-M) value, decreases by more than the monomer depletion factor with increasing percent conversion. On the contrary, the three highest conversions show above-average o v e r a l l rates which may indicate that the reaction proceeds with a modest acceleration i n rate as the retarders are used up or become

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

338

RING-OPENING POLYMERIZATION

TABLE I CONVERSION-DOSE DATA AND POLYMER MOLECULAR WEIGHTS IN THE RADIATION-INDUCED POLYMERIZATION OF (+)-LIMONENE OXIDE

Code No.

Temp °C

Dose Mrad

Percent Conversion—

G(-M) monomer molecules 100 eV

Hh-

1-1

25

1.355

79.3

3711

1-2

25

0.927

32.7

2239

1-3

25

1.823

77.5

2695

1-4

25

0.464

13.0

1776

II-l

25

1.840

51.0

1757

II-2

25

1.592

67.0

2668

2302

II-3

25

0.852

28.7

2136

1443

II-4

25

1.226

54.0

2793

2838

II-5

-196

1.991

III-l

25

3.715

III-2

-78

25.50

12.0

III-3

0

3.68

21.3

1.6 47.5

—Based on recovery of p r e c i p i t a t e d

polymer.

1163

DP

n

7.6

15.1 9.5 18.7

51 819 30 368

1201

7.9

1618

10.6

2333

15.3

—By vapor pressure osmometry.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24.

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339

less e f f e c t i v e . It i s noteworthy that very high conversions (at least 80%) to polymer can be achieved. This suggests that side reac­ tions giving non-polymerizable products are r e l a t i v e l y unimportant i n the present case. The expectation that the radiation-induced polymerization proceeds by a cationic mechanism was substantiated by an experiment i n which 1.5 volume % of tri-n-propylamine was added to a monomer sample. Even after a dose or more than 10 Mrad, no polymer was recovered by the usual p r e c i p i t a t i o n technique. An estimate of the k i n e t i c chain length ν can be made by d i v i d ­ ing the G(-M) value by the 100-eV y i e l d of free ion i n i t i a t o r s , Gj[. The l a t t e r quantity i s generally considered to be i n a narrow range between 0.1 and 0.2 (1_>.2>_5>6) at least for non-spherical molecules having low d i e l e c t r i c constants i n the l i q u i d phase. The polymerization of limonene oxide at 25°C i s therefore characterized by ν values on the order of 10** · Even allowing for th 1 are a l l between 7.6 an thousand-fold smaller than the estimated k i n e t i c chain length. Accordingly, a high frequency of chain transfer must be involved i n the polymerization and this i s consistent with a cationic mechanism. ot-Pinene Oxide. As seen from a comparison of the results i n Table II with those i n Table I, the radiâtion-induced polymerization of α-pinene oxide proceeds at a much slower rate than limonene oxide under the same conditions. The mean value of G(-M) for a-pinene oxide calculated from the 12 runs at 25°C i s 360 with a standard deviation (N - 12 weighting) of 121. On average, therefore, the polymerization rates or ^(-M) values for these two monomers d i f f e r by a factor of 6.9. At 0°C the (J(-M) values for α-pinene oxide are s l i g h t l y lower than the average value at 25°C but remain well within the standard deviation for the l a t t e r set of measurements. Again, no d e f i n i t e trend regarding the temperature dependence of G(-M) i s evident from these limited data. Although the polymerizations were carried through to t o t a l conversions not exceeding 33.6% i n this case (Table I I ) , no s i g n i f i ­ cance should be attached to this feature of the r e s u l t s . Higher conversions would have undoubtedly been attained i f the i r r a d i a t i o n doses had been increased proportionately. The average DP of 5.6 for the α-pinene oxide polymer formed at 25°C (Table II) i s lower than the corresponding average of 11.8 for the limonene oxide polymer (Table I ) , this being also the order of the polymerization rates for these two monomers. However, the ratio (2.1) of molecular weights i s somewhat less than the r a t i o (6.9) of G(-M) values. Despite these differences, the inequality ν » DP applies to both monomers. Thus, the k i n e t i c chain length (v 2 χ 10 ) for α-pinene oxide polymerization i s about 350 times larger than the average DP (5.6), again indicating the importance of chain transfer. Although only two measurements were made, the molecular weights of the α-pinene oxide polymers prepared at 0°C (Table II) appear to be s i g n i f i c a n t l y higher (average DP of 13.4) than those prepared at 25°C. More data would be needed, however, to establish this point unequivocally. f

n

n

2

n

n

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

340

TABLE I I CONVERSION-DOSE DATA AND POLYMER MOLECULAR WEIGHTS IN THE RADIATION-INDUCED POLYMERIZATION OF a-PINENE OXIDE

Temp °C

Dose Mrad

1-1

25

3.26

1-2

25

1-3

M

b

DP

Percent Conversion—

G(-M) monomer molecules 100 eV

3.27

7.6

148

-196

4.21

5.6

85

1-4

25

4.36

10.9

159

II-l

25

3.09

19.3

395

II-2

25

1.48

10.0

428

II-3

25

3.00

14.4

304

500

3.3

II-4

25

5.11

21.7

270

1933

12.7

III-l

25

5.83

34.5

375

305

2.0

III-2

25

3.92

24.5

396

880

5.8

III-3

25

3.92

33.6

544

III-4

25

5.83

30.0

326

IV-2

25

3.16

22.3

447

632

4.2

IV-3

0

3.71

19.5

333

2457

16.1

IV-4

0

4.05

19.9

312

1628

10.7

Code No.

—Based on recovery of p r e c i p i t a t e d

polymer.

η

η

—By vapor pressure osmometry.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24.

Radiation-Induced Cationic Polymerization

AIKINS AND WILLIAMS

341

β-Pinene Oxide. From twelve determinations l i s t e d i n Table I I I , the mean value of G(-M) at 25°C for this monomer i s 461 with a stan­ dard deviation (N = 12 weighting) of 308. The polymerization rates are therefore quite comparable to those found for α-pinene oxide (Table I I ) . This s i m i l a r i t y also applies to the DP values, the average value of 4.0 for the β-pinene oxide polymer at 25°C being s t a t i s t i c a l l y Indistinguishable from the results for the a-pinene oxide polymer i n Table II with an average of 5.8. It i s interesting that the highest G(-M) value of 1342 was obtained i n a high conversion (80.4%) experiment. This result supports the point made e a r l i e r for limonene oxide that the radia­ tion-induced polymerization of these monomers can be carried nearly to completion, certainly without any diminution i n rate and possibly even with rate enhancement as impurities are used up. The polymerization rate was strongly retarded by the addition of 1.0 volume % tri-n-propylamlne to the monomer. In contrast to a "control" sample (IV-3 i after a dose of 3.99 Mrad polymer after exposure to the same t o t a l dose. Also, this small amount of polymer produced i n the presence of the amine did not precipitate out immediately on the addition of methanol, and i t was recovered only after the solution had been allowed to stand for several days. Since the £(-M) value calculated for the amine-doped sample i s only 22.6 as against the "control" value of 557, i t i s clear that the chain character of the polymerization i s seriously impaired by the amine. n

Structural Characterization of Polymers 1

H-NMR Studies 1

(+)-Limonene Oxide. The H-NMR spectra of limonene oxide and i t s radiation-produced polymer are shown in Figures 1(a) and (b). In each case there are strong resonances at 1.66-1.71 and 4.65-4.71 δ which can readily be assigned to the methyl and vinylidene protons, respectively, of the pendant isopropenyl ( Ο Ή Η > Ο Η ) group. This comparison c l e a r l y demonstrates that the polymerization does not proceed by addition to the vinylidene double bond. The other two well-defined peaks at 1.19 and 3.5 δ i n the polymer spectrum are assigned to the CH3-C-O and H-C-0 protons at the C-l and C-2 carbons of the cyclohexane ring i n the repeat unit produced by opening the epoxide r i n g . Incidentally, the corresponding methyl protons i n the monomer are responsible for the strong doublet resonance seen at 1.274-1.292 δ. α-Pinene Oxide. Figures 2(a) and 2(b) show the H-NMR spectra of poly(a-pinene oxide) and i t s monomer. In the monomer spectrum there are two well-separated peaks from methyl protons at 0.955 δ and 1.296-1.313 δ. Integration snowed that the absorption from the l a t t e r group of resonances was exactly double that of the 0.955 δ peak. Since there are three non-equivalent methyl groups i n a-pinene oxide, the resonances from two of these must overlap at « 1.3 δ. By analogy with the assignment of the =* 1.28 δ peak in limonene oxide to the methyl group at the epoxide ring, one of the resonances at * 1.3 δ i n α-pinene can be s i m i l a r l y assigned. Thus the gem-dimethyl group 3

2

1

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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RING-OPENING POLYMERIZATION

TABLE I I I CONVERSION-DOSE DATA AND POLYMER MOLECULAR WEIGHTS IN THE RADIATION-INDUCED POLYMERIZATION OF &-PINENE OXIDE

Code No.

Dose Mrad

Percent

1-2

25

5.14

24.7

304

1-3

25

4.18

25.6

388

1-4

25

3.39

20.0

373

II-l

25

0.88

2.7

195

II-2

25

1.76

8.2

294

II-3

25

2.65

8.9

213

II-4

25

3.53

8.2

147

III-l

25

3.80

80.4

1342

III-2

25

4.44

46.9

670

750

4.9

111-3

25

4.46

40.3

572

460

3.0

IV-1

25

4.97

37.1

473

IV-3

25

3.99

35.0

557

—Based on recovery of p r e c i p i t a t e d

polymer.

G(-M)

M

b

Temp °C

DP

-By vapor pressure osmometry.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24.

A1KINS AND WILLIAMS

Figure

1.

200 MHz

Radiation-Induced Cationic Polymerization

H - NMR

spectra of (a) (+)-limonene

oxide and

(b) poly(limonene oxide)

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

343

RING-OPENING POLYMERIZATION

344

Figure

2.

200 MHz H - NMR spectra of (a) α-pinene oxide and (b) poly(α-pinene oxide)

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24.

AIKINS A N D W I L L I A M S

Radiation-Induced Cationic Polymerization

345

must absorb at 0.96 and 1.30 δ. These assignments agree with those of Ruckel et^ a l . (14) but do not correspond with those given i n the Sadtler compilation (17) which mistakenly assumes that the gem-di­ methyl protons are equivalent and are responsible for the entire 1.3 δ peak· Turning to the polymer spectrum, there are prominent peaks displayed at δ values of 0.728, 0.956, 1.16, 1.59, 1.76, 3.84, 4.7, 5.21, and 5.54. Following Ruckel et^ a l . (14), i t i s helpful to consider the assignments f i r s t i n terms of the rearranged repeat unit 4_. On the basis of the close correspondence with the resonance at 1.14 δ i n the spectrum of poly(isobutylene oxide) (14), the very strong peak at 1.16 δ can be assigned to the protons from the gem-di­ methyl group i n the above structure. The protons from the remaining methyl group adjacent to the double bond would be expected to absorb at about 1.6 δ according to the H-NMR spectrum of limonene [5] which has a resonance at abou methyl group (18). Therefore o l e f i n i c methyl i n the rearranged structure 4^. Further evidence for the rearranged repeat unit 4^ i n the α-pinene oxide polymer comes from the observation of resonances at 5.21 and 5.54 δ which are c h a r a c t e r i s t i c of c y c l o - o l e f i n i c hydro­ gens. For example, there i s a similar resonance at 5.39 δ i n limonene (18) (j)-mentha-l(2) ,8(9)-diene, 5) which again serves as a suitable model compound for the cyclohexene portion of this rear­ ranged unit. Therefore, one of the above resonances almost c e r t a i n l y corresponds to the c y c l o - o l e f i n i c hydrogen depicted i n the above structure while the other probably arises from an isomeric structure formed by a s h i f t of the double bond, as suggested by Ruckel et a l . (14). The presence of two H-C-0 resonances at 3.8 - 4.0 δ i s also supportive of two kinds of c y c l o - o l e f i n i c repeat structures. Hitherto, our assignments of the H resonances i n the α-pinene oxide polymer have corresponded closely to those of Ruckel et a l . (14), the spectra of the two d i f f e r e n t l y prepared polymers being very similar i n a l l respects except for an additional peak at 1.30 δ i n the previous work. We d e f i n i t e l y do not find such a peak i n the radiation-produced polymer, and i t i s curious that the previous workers also reported (14) that for polymer prepared under certain c a t a l y t i c conditions, this 1.30 δ peak was either t o t a l l y absent or only a trace of i t was found i n the spectrum. However, Ruckel et^ a l . (14) assumed that since the peaks at 0.97 and 1.30 δ i n their polymer corresponded almost exactly to the positions of the gem-di­ methyl group resonances in the monomer, these peaks could be assigned to the same group i n the ring-closed or unrearranged repeat unit 6· These authors went on to estimate the percentage of such ring-closed structures i n the polymer from the relative intensity of the 1.30 δ absorption. It i s questionable, however, that the positions of the gem-di­ methyl H resonances remain unchanged i n going from the α-pinene oxide monomer to the ring-closed polymer structure JS, one reason being that the opening of the epoxide ring results i n a different placement of the gem-dimethyl group relative to the oxygen atom. Therefore, i n contrast to the previous assignment (14), we propose that these methyl *H resonances i n 6^ can be attributed to the peaks 1

1

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

346

RING-OPENING POLYMERIZATION

of comparable intensity at 0.728 and 0.956 δ. This would not only account for the absence of the 1.30 δ peak i n our samples, and i n some of Ruckel s polymers (14,19), but also explain why the 0.73 and 0.96 δ peaks are always present together i n the spectra of both types of polymers. Moreover, the present set of assignments obviates the need to explain the methyl resonance at 0.73 δ i n terms of various ring-expanded repeat structures (14). The only well-defined peaks i n the poly(α-pinene oxide) spectrum which remain to be assigned are those at 1.76 and 4.70 δ. These resonance positions correspond almost precisely to those observed f o r methyl and o l e f i n i c protons i n an isopropenyl group, as discussed e a r l i e r for limonene oxide and i t s polymer. Accordingly, we assign these peaks to isopropenyl end groups produced by chain (proton) transfer from a ring-opened propagating cation (see Discussion). I t might be noted that Ruckel et a l . (14) assigned the 1.7 δ peak to a CH3-OC resonance i n a branched mer and the 4.64 δ peak to an H-C-0 resonance· β-Pinene Oxide. Th presented together i n Figures 3(a) and 3(b). In addition to the two strong peaks at 0.922 and 1.246 δ which can be assigned to the gem-dimethyl group, the monomer spectrum consists of two well-defined doublets ( J » 5 Hz) centered at 2.579 and 2.745 δ as well as some weaker resonances i n the intermediate 1.5-2.5 δ region. The doublets are almost certainly due to the two nonequivalent exocyclic CH2 hydrogens of the epoxide group. The polymer spectrum i s noticeably simpler than that of poly(apinene oxide) i n Figure 2(b). In particular, only one strong reson­ ance at 1.127 δ appears to originate from methyl hydrogens i n the poly(fl-pinene oxide). This i s confidently assigned to the gem-di­ methyl group i n the ring-opened repeat unit 7_ since the 1.127 δ resonance occurs at almost the same chemical s h i f t as the 1.14 δ peak from the corresponding group i n poly(isobutylene oxide) (14). There are two other prominent resonances i n the polymer spectrum which are compatible with structure 7_, namely the 3.729 δ peak which can be assigned to the hydrogens of the - O C H 2 - group, and the 5.68 δ peak which i s s p e c i f i c for the c y c l o - o l e f i n i c hydrogen. Of the remaining peaks, those at 1.729 and 4.702 δ are again characteristic of terminal isopropenyl groups produced by chain transfer from a r i n g opened cation. It should be noted that the resonances observed at 0.95 and 1.25 δ i n the spectrum of the catalytically-prepared polymer (14) are v i r t u a l l y absent i n the present case. These peaks coincide closely with the strong methyl resonances i n the β-pinene oxide monomer (Figure 3(a)), and so i t i s conceivable that they arise from contam­ ination by monomer. In a study of the polymerization of β-pinene (13), for instance, i t was found that the polymer had to be reprecipitated from solution i n order to remove a l l traces of monomer. However, Dr. Ruckel has informed us i n a private communication that great pains were taken to remove monomer from the c a t a l y t i c a l l y - p r e ­ pared polymer (14). Another difference between our results and those of Ruckel et a l . (14) concerns the r e l a t i v e intensity of the o l e f i n i c resonance i n the poly^-pinene oxide) spectrum. They reported that i t was only 30% of that expected for the ring-opened structure and this l e d 1

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24. AIKINS AND WILLIAMS

Radiât ion-Induced Cationic Polymerization

K M -

r-

Me

Me

ci,.

—ι—ι—ι—ι—j—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—I—ι—ι—ι—ι

3.0

2.5

2.0

1.5

1.0

I ι ι ι ι I '

0.5

0.0

PPM

Τ" PPM Figure

3.

l

200 MHz H - NMR spectra of (a) β-pinene oxide and (b) poly(β-pinene oxide)

American Chemical Society Library In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Society: 1155 Chemical 16th St.. M.W.Washington, DC, 1985.

348

RING-OPENING

POLYMERIZATION

them to postulate a second propagation pathway through a rearranged b i c y c l i c structure. However, i t appears from a comparison of Figures 2(b) and 3(b) that the relative intensity of the 5.68 δ peak i n poly(3-pinene oxide) is equal to or s l i g h t l y greater than that derived from the sum of the two o l e f i n i c peaks in poly(a-pinene oxide). Taken together with the apparent absence of gem-dimethyl absorption from b i c y c l i c structures i n the spectrum of poly(3-pinene oxide), our H-NMR results seem to be consistent with the epoxide ring-opening being followed by a predominant cyclobutane ring-opening propagation step i n the radiation-induced polymerization of 3 pinene oxide. -

13

C-NMR Studies 13

(+)-Limonene Oxide. The proton-decoupled C-NMR spectrum of poly((+)-limonene oxide) i s shown i n Figure 4(a). If the polymerization takes place through the epoxide group, as expected, the repeating unit w i l l be as shown i group at C-4, the numberin In this case the C resonances of C-8, C-9, and C-10 should have very similar chemical s h i f t s to the values for limonene [5], which are located at 149.9, 108.4, and 20.7 ppm ( δ ) , respectively (20). In fact, these resonances match up very well with those at 149.3, 108.5, and 20.94 ppm i n Figure 4(a), reinforcing the conclusion reached e a r l i e r from the H-NMR studies that the isopropenyl group i s present i n the repeating unit 8^ of poly(limonene oxide). In view of the average DP of 11.8, i t may be d i f f i c u l t to detect C resonances from end groups in poly(limonene oxide). These end groups would be expected to consist of olefins produced by chain transfer, and C resonances from o l e f i n i c carbons should be i n the low-field region of the spectrum. There is only one unassigned peak at 150.93 ppm which would f i t this description, however, and i t s assignment must be tentative. One p o s s i b i l i t y i s that i t arises from an o l e f i n end group formed between C-l and C-7, a very low-field resonance being expected for o l e f i n i c carbons not attached to hydro­ gen ( — Ο ). α-Pinene Oxide. Several peaks i n the spectrum ( F i g . 4(b)) of poly(α-pinene oxide) have very similar chemical s h i f t s to those l i s t e d by Ruckel et^ a l . (14) for the c a t a l y t i c a l l y prepared polymer. Moreover, as shown i n Table IV, several peaks again correspond close­ ly to the C resonances in sobrerol [10], a model compound possess­ ing the polymer repeating unit 4. For example, the peaks at 132.8 and 133.9 ppm can be assigned to the methyl-substituted o l e f i n i c carbon i n j4 since the resonances from the corresponding C-l i n limonene (20) and sobrerol (14) occur at 133.5 and 134.8 ppm, respec­ t i v e l y . In addition, the peaks at 148.36, 108.5 (two), and 19.67 ppm can be assigned to isopropenyl end groups, these C resonances having very similar chemical s h i f t s to those described above for poly(limonene oxide). F i n a l l y , the farthest upfield C resonance at 12.5-12.6 ppm was assigned by Ruckel et a l , (14_) to an angular bridgehead methyl group on the basis of similar chemical s h i f t s for the resonance from C-10 i n bornane, bornylene, and camphor (21). β-Pinene Oxide. An examination of the spectrum i n Figure 4(c) reveals resonances at 150, 108, and 21 ppm which we have previously assigned (see limonene oxide) to the carbons of isopropenyl groups. 1 3

0

1

n

1 3

1 3

1 3

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24. AIKINS AND WILLIAMS

Radiation-Induced Cationic Polymerization

349

-0—CH 2

Me

-ι—ι—J—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι—ι 140 120 100 80 60 40 20 0 13 Figure 4a.

200 MHz

C-NMR

spectra of poly (limonene oxide).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

PPM

RING-OPENING POLYMERIZATION

13

Figures 4b and 4c. 200 MHz C-NMR spectra of poly(a-pinene oxide) and poly(/3-pinene oxide) .

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

24. AIKINS AND WILLIAMS

Radiation-Induced Cationic Polymerization

351

TABLE IV 13

1

t

C CHEMICAL - SHIFT DATA (PPM) FOR SOBREROL AND POLY(a-PINENE OXIDE) SAMPLES

Sobrerol ** [10J

Poly(a-pinen

oxide)

Poly(a-pinen

oxide)

11

catalytic polymerization * radiation-induced polymerization > i

—'

Me

CH

21.0

12.6

35.6

12.5

70.9

CH

26.0

19.8

38.9*

19.7

94.3

CH

27.3

20.1

44.3

21.5

96.1

CH

27.7

20.8

45.2

24.3

108.3

47.0

25.4

108.8

32.5

121.5

35.7

125.6

3

3

2

3

CH

32.8

CH

38.7

CHOH

68.0

2

2

COH

71.5

»CH

124.6

-c
H0-CH-CH -0-CH CH 0H 2

2

2

2

I

2

I

CH C1

Η

2

3 Termination & R e i n i t i a t i o n : The proton i n 3 i s abstracted by ECH to form new ECH-EG adduct g l y c o l , 4, and regenerate the propagating species 2. 3 +

\ /

C

H

2

C

H0-CH-CH -0-CH CH 0H + 2

1

2

2

2

CH C1 2

4 After a l l EG i s consumed, the regenerated propagating species 2 then reacts with the nascent glycol 4 by a manner i d e n t i c a l to that mentioned above to produce the ne\7 ECH-EG-ECH adduct g l y c o l , 5, and regenerated propagating species 2.

4 + 2

~

v

~

+ HO-CH-CH -0-CH CH -0-CH -CH-OH 2

2

2

2

I I

I CH C1

H

2

CH C1 2

-CH C1 2

HO-CH-CH -0-CH CH -0-CH -CH-OH 2

I

2

2

CH C1

2

+2

I

CH C1

2

2

5

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

368

RING-OPENING POLYMERIZATION

Overall polymerization proceeds by repeating the "transfer", "termin­ ation" and " r e i n i t i a t i o n " steps schematically as shown below. HO-CH-CH -0-CH CH -0-CH -CH-OH + \ 2

2

2

y

2

CH C1

2

C 1

I H

CH C1

2

C H

2

0

H-fO-CH-CH *_^ 0-CH CH -0 4 0 Η - 0 Η - Ο ί ^ γ Η 2

2

2

2

CH C1

+

\

C

I

CH C1

2

/

According to t h i s new postulated mechanism, a l l results obtained are readily explainable. I t i s reasonable that a l l EG was consumed at the beginning of the polymerization stage, and no EG residue i s located at the terminal p o s i t i o n of the polymer chains. Small amounts of primary hydroxyl groups observed i n PECHG are probably due to opening of the oxirane CH-0 linkage i n the propaga­ ting species: ^/^0-CH -CH-CH Cl ' I predominantly OH 2

• — 7 CH C1 1 ^ pi 2 +0 2

2

v/^0-CH-CH 0H 2

I

CH C1 2

The oligomers are believed to be formed by so-called back-biting or t a i l - b i t i n g which i s supposed to produce hydroxyl-terminated l i n e a r oligomers as well as non-functional c y c l i c oligomers. Absence of any hydroxyl-terminated l i n e a r oliogomers i n PECHG can be explained as follows: since hydroxyl groups are polymer propagating sites, hydroxyl-terminated l i n e a r oligomers can p a r t i c i p a t e back into the polymerization as soon as they are formed, while non-functional c y c l i c oligomers cannot. Thus oligomers found i n PECHG are only non-functional c y c l i c oligomers. These c y c l i c oligomers can form only when polymer molecular weight exceeds approximately 1000. According to the newly postulated mechanism, PECHG possessing the molecular weight of approximately 1000 has two polyepichlorohydrin chains each possessing -500 molecu­ l a r weight at both ends of EG residue.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

25. OKAMOTO

369

Cationic Polymerization of ECH

Hi0-CH-CH i-5-0-CH2-CH2-0-{CH2-CH-0r-5H

I

I

2

CH C1

CH C1

2

2

PECHG -1000 molecular weight

These two polymer chains are too short to form c y c l i c oligomers such as cyclopentamer and cyclohexamer. No c y c l i c oligomers were, there­ fore, observed i n PECHG possessing the molecular weight of -1000. C y c l i c oligomers formation starts taking place when molecular weight of PECHG exceeds -1000. The above r a t i o n a l i z a t i o sults. For example, thre molecular weight of 150 y c y c l i oligomers

H+O-CH-CHgl-r 0-CH -CH-CH -0 -ÎCH -CH-0f~ H

I

I

CH C1 2

2

2

2

I

I CH C1 0-fCH -CH-0f-_H 2

2

~

I

5

CH C1 2

polyepichlorohydrin t r i o l -1500 molecular weight

Polyepichlorohydrin Polyols By u t i l i z i n g the new findings mentioned above, PECHG and polyepi­ chlorohydrin t r i o l (PECHT), each with a molecular weight of approxi­ mately 1000, were prepared using ethylene g l y c o l and g l y c e r o l , respectively. The results are summarized i n Table I I I .

Table I I I . Polyepichlorohydrin Polyols

PECHG Molecular weight (Mn) Hydroxy equivalent weight Hydroxy f u n c t i o n a l i t y Hydroxy group, primary secondary Dispersity (Mw/Mn)

954 477 2.0 6.6% 93.4% 1.29

PECHT 1010 335 3.0 6.5% 93.5% 1.12

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

370

RING-OPENING POLYMERIZATION

Attempts to prepare polyepichlorohydrin t e t r a o l , pentaol, and octaol using pentaerythritol, glucose, and sucrose, respectively were unsuccessful, probably due to the poor s o l u b i l i t y of s t a r t i n g polyols in ECH. Conclusion A l l results mentioned above c l e a r l y support the new mechanism of cationic ring-opening polymerization of ECH i n the presence of EG used as a molecular weight modifier. Polymerization i n i t i a t e s at the hydroxyl groups i n EG and the polymer chain propagates simultaneously at both ends through the addition of the monomer. Since this poly­ merization possessed a c h a r a c t e r i s t i c of l i v i n g polymerization, i . e . polymer molecular weight increased d i r e c t l y with polymer conversion, the polymer molecular weight was readily controlled by adjusting the r a t i o of ECH to EG. The obtained molecular weight PECHG possessed predominantly secondar d i s t r i b u t i o n , and a hydroxy Experimental Reagents. Epichlorohydrin was dried over molecular sieves. Ethylene g l y c o l , reagent grade, was used as received. 2-Butene-l,4-diol and 2-butyne-l,4-diol were freshly d i s t i l l e d before used. TEOP (rap 140142°C) was reprecipitated from methylene chloride and ether, and borontrifluoride etherate was d i s t i l l e d before use. Polymerization. Polymerization was carried out i n a 250 mL 3-neck flask, equipped with a mechanical s t i r r e r , a thermometer, and a rubber septum for i n i t i a t o r introduction. ECH, 93.8 g, and EG, 6.2 g, were charged into a flask and the flask was purged with dry nitrogen. The i n i t i a t o r solution, 0.045 g of TEOP dissolved i n 5 mL of methylene chloride, was added to the above mixture incrementally (1 mL per every 5 min) by a hypodermic syringe while maintaining the temperature at 30°C. The polymerization was carried out at 30°C and the reaction was monitored by taking small amounts of sample during the polymerization. On completion of the polymerization, the reac­ t i o n was terminated with -300 μΐ of a mixture of 30% ammonium hydrox­ ide and isopropanol (1:4 by v o l ) , and then the polymer was dried on a rotary evaporator at 60°C i n vacuo. The obtained PECHG possessed a molecular weight of 950 determined by vapor pressure osmometry (THF solvent), hydroxyl number of 118, and molecular weight d i s t r i b u t i o n , Mw/Mn, of 1.23. Determination of Hydroxyl Groups. Type of hydroxyl groups i n PECHG were determined using a Bruker WH-200 superconducting NMR spectrome­ ter employing the trichloroacetylisocyanate d e r i v a t i z a t i o n method (15). Typical NMR spectrum was shown i n Figure 7. I d e n t i f i c a t i o n of Oligomers. The low molecular weight f r a c t i o n was separated by a preparative GPC and i d e n t i f i e d using a Finnigan MAT 311A f i e l d desorption mass spectrometer (FD-MS).

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

25.

OK A MOTO

371

Cationic Polymerization of ECH

Molecular Weight Determination. Molecular weights were determined using a Waters Model 200 gel permeation chromatograph equipped with a modified Waters R4 d i f f e r e n t i a l refractometer detector. The solvent was THF; the flow was 2.0 mm /min. The column, 25 cm χ 7.8 mm ID, consisted of 10 , 10 , 10 , 10 , 10 A° waters microstyragel. 3

6

5

4

3

2

Disappearance of Molecular Weight Modifier. Hydroxyl number was determined using a standard procedure (1_6) . Disappearance of molecu­ l a r weight modifier was calculated by dividing the polymer hydroxyl number by the t h e o r e t i c a l hydroxyl number. I t was assumed i n calcu­ l a t i n g the t h e o r e t i c a l hydroxyl number that a l l molecular weight modifier was incorporated into the polymer obtained.

0 II R-CH -0-CNHC0CI 2

|-— -{-O-CHg-CH-^ CH CI

3

2

^CH-O-CNHCOC^

SECONDARY PRIMARY

I

Figure 7.

BACKBONE

I

*H NMR spectrum of polyepichlorohydrin glycol derivatized with trichloroacetylisocyanate: CDC1 solvent. 3

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

372

RING-OPENING POLYMERIZATION

Acknowledgments The author would l i k e to thank Dr. M. P. Dreyfuss who generously shared his expertise, Dr. D. Harmon and Mrs. B. Boose for GPC analy­ ses, Dr. R. Lattimer for FD-MS analyses, Mr. J . Westfahl for NMR analyses, and Mrs. R. Lord f o r carrying out the experiments. The author wishes to express his appreciation to the BFGoodrich Chemical Group for permission to publish this work.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

12. 13.

14.

15. 16.

Dreyfuss, P. U.S. Patent 3 850 856, 1974. Young, C. I.; Barker, L. L. U.K. Patent Application 2 021 606, 1979. Manser, G. E.; Guimont J . ; Ross D L Presented at the 1981 JANNAF Propulsion Meeting Dickinson, L. A. J Hammond, J . M.; Hooper, J . F.; Robertson, W. G. P. J . Polymer S c i . A-1 1971, 9, 265. Beste, L. F.; H a l l , Η. Κ., J r . J . Phy. Chem. 1964, 68, 269. Ito, K.; Usami, N.; Yamashita, Y. Polymer J . 1979, 11, 171. Dreyfuss, P.; Dreyfuss, M. P. Polymer J . 1975, 8, 81. Robinson, I. M.; Pruckmayr, G. Macromolecules 1979, 12, 1043. Goethals, E. J . "Advances i n Polymer Science", Springer-Verlag B e r l i n Heidelberg, New York, 1977; Vol. 23, pp 104-130. Penczek, S.; Kubisa, P.; Matyjaszewski, K. "Advances i n Polymer Science", Springer-Verlag B e r l i n Heidelberg, New York, 1980; Vol. 37. Jones, F. R.; Plesch, P. H. Chem. Commun. 1969, 1231 and J . Chem. Soc., Dalton 1979, 927. Meerwein, H. "Houben-Weyl Methoden der Organischen Chemie.", E. M i l l e r Ed., Stuttgart, George Thieme Verlog, 1965; Vol VI/3, pp 359. Penczek, S.; Kubisa, P.; Matyjaszewski, K. "Advance i n Polymer Science Cationic Ring-Opening Polymerization", Springer-Verlag B e r l i n Heidelberg, New York, 1980; Vol. 37, p 6. Groom, T.; Babiec, J . S., J r . ; Van Leuwen, B. G. J . of C e l l u l a r P l a s t i c s 1974, January/February, 43. Sorenson, W. R.; Campbell, T. W. "Preparative Method of Polymer Chemistry", 2nd Ed., Interscience Publisher, a d i v i s i o n of John Wiley & Sons, New York, London, Syndey, Toronto, 1968; p 155.

RECEIVED October 4, 1984

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

26 Lactone Polymerization Pivalolactone and Related Lactones WILLIAM H. SHARKEY

1

Central Research and Development Department, Ε. I. du Pont de Nemours & Company, Wilmington, DE 19898 The polymerization of pivalolactone, α, α-dimethyl-ß-propiolactone, i s a remarkably easy anionic, ring-opening reaction that takes place rapidly and completely i n organic media at mild temperatures Since it appears to be simila and the properties of i t than those of other ß-lactone polymers, the formation and properties of polypivalolactone w i l l be emphasized i n this discussion. Early studies on pivalolactone (1,2) established that i t s polymerization i s i n i t i a t e d by t e r t i a r y amines and phosphines. The reaction was visualized as occurring i n two steps.

The formation of a macrozwitterion by attack of the nucleophile on the methylene group of PVL has been supported by NMR and chemical studies on propiolactone. By these means Maskevich, Pakhomeva, and Enikolopyan (3) who used triethylphosphine and Mathes and Jacks (4) who used triethylamine, obtained evidence for the i n i t i a t i o n 1

Current address: 174 S. Collier Blvd., Marco Island, FL 33937 0097-6156/85/0286-0373$06.00/0 © 1985 American Chemical Society

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

374

RING-OPENING POLYMERIZATION

reactions. In addition, Mathes and Jacks (5) used betaine, + (CH3)3NCH2C02~", as an i n i t i a t o r for propiolactone and showed by electrophoresis that quaternary ammonium cations and carboxylate ions are present in the same polymer chain. The formation of polymeric zwitterions might be thought as unlikely because of high coulombic energy of charge separation. Mayne (6) has pointed out this need not be so because the chains may be cyclized or paired with each other as indicated below.

or

v .

+ - ~ +

etc.

Mayne has also shown the raacrozwitterions to be l i v i n g polymers. He has used PVL oligomers of Mn 2000-7000 suspended in refluxing hexane as i n i t i a t o r weight PPVL. He has state faster than i n i t i a t i o n by tributylphosphine by a factor of at least 600. This behavior i s a consequence of the high r e a c t i v i t y of the carboxyl anion toward the lactone. It has been recognized by a l l investigators of beta-lactone polymerization that carboxyl ions are the i n i t i a t o r s and that they are most effective when used as tetralkylammonium s a l t s . Before pursuing this point further, an interesting variation on t e r t i a r y amine i n i t i a t i o n should be mentioned. Thus c y c l i c amine i n i t i a t i o n was reported by Wilson and Beaman.(7^) These authors showed that c y c l i c t e r t i a r y amines which undergo easy thermal ring opening can be used to synthesize amine-containing copolymers. This scheme i s i l l u s t r a t e d below with quinuclidene. The f i r s t step i s to make a macrozwitterion. CH

CH3

3

\/ C

CHo

y

IN

+

CH

^C=0

2

CHo

-^^N-(-CH -C-C027-CH -C-C02 2

^ 0

2

CH3

η

CH

3

In the second step, the polymer i s heated in a c e t o n i t r i l e under reflux for several hours. CH3

•^N^N-^CH2-C-C02^-CH2-C-C0 " 2

CH3

CH3 -ν ^ Η 0 Η - ^ 2

2

CH3

^N-^CH -Ç-C02-)-CH2-Ç-C02~| m 2

CH3

CH3

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

26.

SHARKEY

Lactone Polymerization

375

A number of strained-ring, t e r t i a r y amines were investigated including a z i r i d i n e s , azetidines, p y r r o l i d i n e s , conidine, cycloamphidine, and isogranatanine. Copolymers were obtained containing 7 to 58 i n i t i a t o r units per polymer chain. Polymerization Mechanism As stated above, i t has been established that carboxylate ions are the true i n i t i a t o r s i n β-lactone polymerization. In an early study, H a l l (8) stated that in intermediate pH ranges anions or water i t s e l f attack the CH2 group with alkyl-oxygen cleavage by SN reaction that proceeds most rapidly i n anhydrous a c e t o n i t r i l e or tetrahydrofuran. From heats of combustion he determined the heat of polymerization of pivalolactone* ΔΗχ to be -20.1 kcal mol" . Mayne (6) gives a value of -18.4 kcal mol" and the value for polymerization of propiolactone (9) i s -18.4 kcal mol" Because the heat o use a calorimetric metho The process can be described by i n i t i a t o r I attacking the β-lactone M to give the β-substituted carboxylate IM^, which attacks additional monomer molecules to give the poly-β-lactone IM . In those cases when kp i s only s l i g h t l y less than k^, the 2

1

0

1

1

2

I + M



IM^ + M

ΙΜχ

IM

2

Initiation

Propagation

polymerization w i l l proceed according to approximate f i r s t - o r d e r k i n e t i c s and for them only k^ was reported. For some i n i t i a t o r s under certain conditions k^ differed markedly form kp and here the treatment of Beste and Hall (12) was followed. Typical results are described in Table I where k^ and kp are in M s e c " . The data indicates the polymerization rate i s very high and substantially higher i n THF than i n a c e t o n i t r i l e . Bigdeli and Lenz (13) have also examined the polymerization k i n e t i c s of β-lactones. They used an IR method (14) and their results support, in broad outline, Hall's findings. Their numbers are d i f f e r e n t , but they confirm that PVL polymerizes rapidly and that THF i s a better solvent than DMSO. This i s shown in Table II where k i s expressed in M" s e c " . Note that α-methyl-or propyl^-propiolactone polymerizes most rapidly i n THF. Inasmuch as the polymerization of β-lactones, and pivalo­ lactone in p a r t i c u l a r , i s very rapid, the question arises as to how -1

1

1

1

p

*Unpublished work at Haskell Laboratory for Toxicology and Industrial medicine, Ε. I. du Pont de Nemours and Company, has shown that pivalolactone caused skin tumors in mice when applied as a 25% solution in acetone for most of the l i f e span of the mice. The time required for tumor formation was greater than that for β-propiolactone.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

RING-OPENING POLYMERIZATION

Table I a

Rate Constants

for Polymerization of β-Lactones at 35°( )

Lactone

Solvent ki

PVL

CH3

CH CH CH 2

CHo 2

2

CH3CN

0.36

CH3CN

0.18

k

p

3

C=0 -

/

0

CH3 XH0CH0CH ^C CH C=0 ^0^

TH

2

a

( >Rate constants are M-l sec

Table I I Polymerization Rates for β-Lactones According to B i g d e l i and Lenz (13)

Lactone

Temp °C

PVL

22

DMSO

0.17

22 37

DMSO DMSO

0.20 0.34

37

THF

0.53

CH3 CHo

^CH CH CH 2

. C-0

2

Solvent

(M"

1

1

iec" )

3

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

26.

311

Ixictone Polymerization

SHARKEY

i t compares to other very fast anionic polymerizations. Such a comparison has been presented by Hall (8), which i s reproduced i n Table I I I to which the value for ormethyl-orpropyl-fl-lactone i n THF has been added. Table I I I Rate Constants for Anionic Polymerizations (8) Propagation Reaction

Temp. °C

Solvent

3

k

i P • M" sec"1

S" + S

THF

25

65,000

ot-MeS" + orMeS

THF

25

830

CH CN THF THF

35 35 37

0.40 0.90 0.53

DMSO

25

0.13

THF

30

0.14

I" + I RCO2 + CH ^ 3

CH

/

/ 2

CH CH CH 2

2

3

3

^C=0

RO" + EO I"Li

a

+

+I

β

S styrene, a,MeS - alpha -methylstyrene, I • isoprene, E 0 « ethylene oxide.

Since rate constants for. PVL i n a c e t o n i t r i l e or DMSO are the same or higher than those of ormethyl-orpropylpropiolactone, the polymerization rate of PVL i n THF should be just as high as that of the methyl, propyl derivative. If this i s so, the above data suggest anionic polymerization of PVL proceeds as fast as anionic polymerization of isoprene i n hydrocarbons to cis-l,4-polyisoprene. This i s indeed quite impressive. A consequence of rapid polymerization i n which k^>kp and the absence of chain transfer to monomer i s the formation of polymer having a Poisson d i s t r i b u t i o n of molecular weights with Mw/Mn only s l i g h t l y above one. Though there i s no chain transfer to monomer, there i s a high degree of chain transfer to polymer. That i s , a l l carboxyl sites i n the system are covered by PPVL chains (15,16)» This i s the result of the rapid exchange between the tetra-alkylammonium salts and free acid groups. This effect i s p a r t i c u l a r l y s i g n i f i c a n t with regard to CO2NR4

+

C0 (PVL) NR 2

n

C0 H 2

4



C0 H + 2

CO2NR4

C0 (PVL) NR4 2

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

n

378

RING-OPENING POLYMERIZATION

synthesis of block copolymers because i t allows quantitative conversion of a beta-lactone monomer to polymer without requiring quantitative conversion of carboxylic acids to s a l t s . In summary, pivalolactone undergoes rapid anionic, r i n g opening polymerization when i n i t i a t e d by tetraalkylammonium carboxylates i n aprotic organic solvents, of which THF i s preferred. The polymer i s l i n e a r , has very low polydispersity, i s " l i v i n g " , and the l i v i n g propagating terminus has exceptionally long l i f e t i m e s . Most, i f not a l l , of these features are also found i n many other substituted β-lactones. Pivalolactone Polymers Polypivalolactone i s a highly c r y s t a l l i n e polymer that exists in three c r y s t a l l i n e modifications; those have been described by Oosterhoff (17) of Shell Laboratories The main product that c r y s t a l l i z e s from a polypivalolacton α-modification. It melt t r a n s i t i o n temperature (Tg) of -10°C. In this form the polymer chains have a h e l i c a l structure with two monomer units per turn. Slow cooling from the melt leads to the β-form, which has a melting point of 228°C. Annealing above 228°C converts the 3-form to the α-form. The γ-form i s raetastable and arises from orientation. In this modification the polymer backbone has a planar zig-zag structure and i s extended 1.6 times with respect to the alpha-form h e l i x . Upon annealing i t reverts to the alpha-form with concomitant shrinkage. As would be expected, this r e v e r s i b i l i t y has a strong influence upon the properties of polypivalolactone. H e l i c a l conformations with two monomer units per turn appear to be general for polymers from β-lactones.(18) Fiber repeat distances may vary, but not by a great amount. Examples are polypropiolactone and poly(D,L-a-methyl-a-n-propyl-p-propiolactone). Both are converted to a planar zig-zag form by stretching and both reverts to a h e l i c a l configuration upon annealing. Molten polypivalolactone, presumably because of i t s high chemical purity, has a much smaller number of nucleation sites than most other polymers. As a consequence spherulites formed during cooling may become quite large. Above 190°C they may grow to 1 mm or larger. Since such large crystals are usually undesirable, i t i s best to avoid them by e f f i c i e n t quenching or by use of nucleating agents. Normal cooling in a mold leads to 75% c r y s t a l l i n i t y and a density (20°C) of 1.19. The density of 100% c r y s t a l l i n e material at 20°C i s reported to be 1.223.(T7) The apparent melt v i s c o s i t y of polypivalolactone over the range of 260-290°C at high shear rates i s below that of poly(ethylene terephthalate).(17) Accordingly, poly(PVL) i s amenable to melt-spinning into fibers and molding into objects. The very high rate of c r y s t a l l i z a t i o n and spherulite growth play an important part in both processes. High linear speeds of spinning and rapid cooling lead to f i b e r s with higher t e n a c i t i e s . Fibers can be easily oriented by stretching over hot plates or hot pins at temperatures of 20 to 210°C. Stretching followed by annealing and stretching again has

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

26.

Lactone Polymerization

SHARKEY

379

led to fibers having very high tenacities (75-90 g./tex) and high moduli up to 1100g./tex . These fibers contain large amounts of the metastable gamma-crystalline form, which can be reconverted to the alpha-form by heat treatment at 150-200°C. The conversion, however, i s accompanied by considerable shrinkage and decreases i n tenacity to 45-55 g./tex (40-50 g/d; 35-44 dN/tex) and modulus to 350 g.tex (315 g/d; 275 dN/tex.). For molded items i t i s best to incorporate nucleating agents to control spherulite s i z e . Injection-molding can be accomplished at temperatures of 260-300°C with mold temperatures of room temperature to 150°C. Oosterhoff (17) has said molecular weights should be between 150,000 and 400,000. Molded polypivalolactone has good strength and modulus and good retention of properties up to 200°C. Annealed samples have exceptionally low set after breaking. This means that test samples revert almost completely to o r i g i n a l dimensions after breaking Block Copolymers The easy formation of polypivalolactone together with i t s rapid c r y s t a l l i z a b i l i t y and good physical properties has stimulated investigations of the attachment of polypivalolactone segments to elastomeric polymers for the purpose of developing new types of thermoplastic elastomers. In these cases the elastomeric component forms the continuous phase and the polypivalolactone blocks c r y s t a l l i z e into discontinuous domains that are the "crosslinks". Included are low-melting $-propiolactone polymers, v i n y l and a c r y l i c polymers, polyisoprene, and poly(isobutylene). Combinations of poly( orme thy 1-or-butyl- 3-propiolactone) (MBPL) and poly(ormethyl-orpropyl-p-propiolactone) (MPPL) as Β blocks and polypivalolactone (poly(PVL)) as A blocks i n ABA block copolymers have been studied by Lenz, Dror, Jorgensen, and Marchessault.(19) They were prepared by using the tetrabutylammonium salt of sebacic acid as a difunctional i n i t i a t o r to i n i t i a t e the polymerization of MBPL or MPPL followed by addition of PVL. Bu4N0 C(CH ) C0 NBu4 2

2

8

2

MBPL Bu4N(MBPL) 0 C(CH ) CO (MBPL) NBu4 n

2

2

8

2

n

PVL Bu N(PVL)—(MBPL) 0 C(CH ) C0 (MBPL)-(PVL) NBu4 η H+ 4

n

2

2

8

2

m

H(PVL)—(MBPL) 0 C(CH ) CO (MBPL)—(PVL) H m η n

2

2

8

2

m

The PVL blocks c r y s t a l l i z e d into domains with good phase separation from either poly(MBPL) or poly(MPPL), which constituted the p r i n c i p a l and continuous phases. The ABA block copolymer with

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

380

RING-OPENING POLYMERIZATION

poly(MPPL) as the Β block behaved as a thermoplastic elastomer but suffered from poor a b i l i t y to snap back quickly from a considerable stretch, i . e . , i t was "logy". Modification of v i n y l and a c r y l i c polymers have included attachment of poly(PVL) blocks to poly(ethylene-co-vinyl acetate-comethacrylic acid).(20) Tetrabutylammonium salts of the copolymer i n THF were reacted with PVL to lead to a copolymer modified with blocks of poly(PVL) along the chain. The highly c r y s t a l l i n e microCHQ

I -^CH CH -)~£cH CH-)~^CH -C-}2

2

2

2

OAc

C0 NBu 2

4

CHQ

I -£CH CH -)--£cH -CH-)~(-CH -C-)2

2

2

2

OAc

C0 (PVL) 2

p

domains of poly(PVL) increased minimum flow temperature, limited s o l u b i l i t y , and reinforced the mechanical properties of the base resin. Caywood (21) has modified poly(ethyl acrylate), poly(ethyl acrylate-co-butyl acrylate), and poly(butyl acrylate) by f i r s t saponifying some of the ester groups by reaction with tetrabutylammonium hydroxide and use of the carboxylic salts so developed to i n i t i a t e the polymerization of pivalolactone. Poly([ethyl acrylate]-g-pivalolactone) was found to be easily processable on conventional rubber working equipment. It was e a s i l y processable on a two-roll m i l l , had excellent calendering properties, could be compression molded at 225-230°C, and could be i n j e c t i o n molded at 225°C. Extrusion was more d i f f i c u l t requiring high temperatures (250°C) and slow extrusion rates. Physical properties of the graft copolymers were similar to those of the parent elastomeric polyacrylates that had been compounded with carbon block and chemically crosslinked. Modification of poly(ethylene-co-propylene-co-l,4-hexadiene) has been described by Thamm and his associates.(22^23) This involved reactions on the side chain unsaturation of Nordel®, DuPont's hydrocarbon elastomer, a copolymer of ethylene, propylene, and 1,4-hexadiene (an EPDM). An EPDM-g-thioglycollic acid was f i r s t made by reaction of the EPDM with large excess of t h i o g l y c o l i c acid using a procedure described by Calhoun and Hewett.(24) This EPDM-T was then reacted with tetrabutylammonium hydroxide i n THF and the product used to i n i t i a t e the polymerization of pivalolactone to give EPDM-g-SCH C0 (PVL) , a hydrocarbon elastomer with poly(PVL) segments distributed randomly along the polymer chain. 2

2

n

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

26.

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Lactone Polymerization

381

A second method for preparing an EPDM-g-(PVL) was reaction of the hydrocarbon polymer with maleic anhydride i n bulk at 260-300°C followed by conversion of the anhydride groups i n the product to tetrabutylammonium salts and use of the salts to i n i t i a t e the polymerization of pivalolactone. n

EPDM:

Maleic Anhydride

EPDM-S: hCHCO

.

>

2. PVL

poly(EPDM-g-PVL):

I (PVL)

n

Tensile strengths of the above products are equal to those of their chemically crosslinked and reinforced non-grafted counterparts. Compression set values of the grafted products, especially after annealing, are unusually low. This indicates the presence of thermally and mechanically stable crosslinks and l i t t l e tendency to form a second network under pressure. Polyisoprene has also been converted to thermoplastic elastomers by attachment of segments of poly(PVL).(25,26) These are of two types, i . e . , ABA triblocks or poly(pivalolactone-b-isopreneb-pivalolactone) and block-graft copolymers or poly[(pivalolactoneb-isoprene-b-pivalolactone)-g-pivalolactone]. Both require a difunctional i n i t i a t o r for converting isoprene to an o - u r d i l i t h i o cis-l,4-polyisoprene. The i n i t i a t o r employed was synthesized by addition of sec-butyl lithium to 1,3-diisopropenyl-benzene followed by reaction with isoprene and modified with triethylamine.(27) I t has the formula: CH3 ^

11^1

CH3 1

(Et3N)o.iLi—isoprene--C-U^H-C—isoprene--Li(Et3N)o.i C H CH-CH2^^^ 2

5

CH CHC H 2

2

5

CH3 CH3 Use of this i n i t i a t o r to polymerize isoprene i n cyclohexane gave polyisoprene of high cis-1,4 content having carbanion on each end of

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

382

RING-OPENING POLYMERIZATION

the polymer chains. Addition of this reaction mixture to tetrahydrofuran saturated with carbon dioxide led to carboxylation at the l i t h i o s i t e s . Conversion of the product to tetrabutylammonium salts and use of these salts to i n i t i a t e pivalolactone gave the desired ABA t r i b l o c k copolymer. Synthesis of the block-graft polymers also started with the difunctional i n i t i a t o r described above. The a , a r d i l i t h i o - c i s - 1 , 4 polyisoprene was then l i t h i a t e d further by reaction with sec-butyl lithium i n the presence of tetramethylethylenediamine. This resulted in the formation of l i t h i o sites randomly spaced along the polymer chains. The complete reaction sequence i s given below. Isoprene Li-Ar-Li

I I TMEDA + sec-BuLi Li—polyisoprene—Li

I Li 1. C02 2. H+ 3. BU4NOH BU4NO2C—polyisoprene—CO2NBU4 CO2NBU4 PVL (PVL) 0 C—polyisoprene—C0 (PVL) n

2

2

n

C0 (PVL) These block-graft polymers were e a s i l y melt-processable, being readily melt spun into e l a s t i c fibers of good strength, high elongation, and high r e s i l i e n c e . For good properties, 35% of PVL or higher appeared desirable. As PVL content was increased, elongation was reduced, which would be expected. Though i t appeared desirable to have at least three or four poly(PVL) segments per chain, l i t t l e difference was observed when larger numbers of segments were employed. Most outstanding properties of these products were high r e s i l i e n c e and good resistance to stress decay. Resilience i s i l l u s t r a t e d i n Figure 1 which shows the s t r e s s - s t r a i n relationship of a poly[(pivalolactone-b-isoprene-b-pivalolactone)-g-pivalolactone] fiber as i t was stretched 300% and then allowed to relax. The shaded area i s the work lost as the fiber was loaded and then unloaded. This area amounts to 13% of the t o t a l , which shows that work recovered was 87%. Such high r e s i l i e n c e compares very favorably with that of chemically-cured natural rubber. 2

n

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

26.

SHARKEY

383

Lactone Polymerization

PIP-q-P YARN (67 DENIER) STRESS vs ELONGATION

100

200 ELONGATION

figure 1.

(%)

S t r e s s - s t r a i n relationship of PIP-g-P f i b e r .

Stress-decay i s i l l u s t r a t e d i n Figure 2. Here the fiber was stretched 300% and the change i s stress requird to maintain that elongation measured as a function of time.

Δ STRESS DECAY CURVE

Δ

^^ν^Δ

ώ PIP-g-P M 57,000 3 4 % PVL n

=RUBBER

0.01

Figure 2.

0.1 HOURS

Stress-decay

10

curve of PIP-g-P f i b e r .

F a l l off i n stress as compared to a sulfur-cured gum rubber control i s compared. Since both decrease at about the same rate, i t i s apparent the c r y s t a l l i n e cross-links i n the block-graft copolymer are as e f f e c t i v e as the chemical cross-links i n rubber. The stress-decay data given i n Figure 2 for poly[pivalolactoneb-isoprene-b-pivalolactone)-g-pivalolactone] was obtained on fibers protected with large amounts of antioxidant. I f a i r autooxidation i s an important factor i n strength loss, use of a polymer backbone

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

384

RING-OPENING POLYMERIZATION

for which autooxidation, minor or existent, should lead to much improved stress decay. Pursuit of this point led to work on poly(isobutylene-g-pivalolactone) compositions.(28,29) Isobutylene was copolymerized with methylbenzenes by cationic methods to give products containing 1-2% of the comonomer. Attachment of polypivalolactone grafts was accomplished using the same chemistry as that for isoprene block-graft copolymers. sec-BuLi

1. C0 , 2 2

4. PVL, 5. H+

:H C0 (PVL) 2

2

n

The poly(isobutylene-co-methylstyrene)-g-pivalolactone polymers were sticky semisolids when amounts of PVL were low, ranged through a rubbery-thermoplastic region as amount of PVL was increased, and were hard, non-elastic solids when PVL content was over 60%. Films obtained by melt-pressing of polymers containing 20-60% PVL were as strong or stronger than conventionally cured polyisobutylene. As i s true with a l l other PVL containing compositions, strength increased markedly upon orientation by drawing. The graft copolymers could be spun into fibers at 250-260°C. These f i b e r s , after orientation by drawing, were not as strong as fibers from the isoprene compositions, but they had tenacities i n the 0.4-0.5 g/d range. Stress-decay on these f i b e r s , determined the same way as for those described i n Figure 2, was only 11% for the f i r s t hour with a further loss of only 5% i n the next 22 hours. Since this loss i s much less than that of the isoprene block-graft f i b e r , which lost over 20% i n 10 hours, i t appears that autooxidation i s a s i g n i f i c a n t factor i n long term stress decay. Acknowledgment s Deep appreciation i s expressed to Professor J . E. McGrath for the i n v i t a t i o n to participate i n this symposium and to R. E. Putscher of the Central Research and Development Department of the DuPont Company for l i b r a r y assistance. Literature Cited 1. 2. 3.

Fischer, N. Thesis, University of Paris, 1959. Reynolds, R. J . W. and Vickers, E. J . , B r i t i s h Patent 766.347, Jan. 23, 1967 assigned to Imperial Chemical Industries. Markevich, Μ. Α., Pakhomera, L. Κ., and Enikolopyan, N. S.,

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

26.

SHARKEY

4. 5. 6. 7. 8. 9.

10. 11. 12. 13. 14. 15.

16.

17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

Lactone Polymerization

385

Proc. Acad. S c i . USSR, Phys. Chem. Sect., 1970, 187 (1-3), 499. Jaacks, V., and Mathes, Ν., Makromol. Chem., 1970, 131, 295. Jaacks, V., and Mathes, Ν., Makromol. Chem., 1971, 142, 209. Mayne N. R., Chem. Tech., 1972, 728. Wilson, D. R., and Beaman, R. G., J . Polymer Science, 1970, A - l , 8, 2161. H a l l , Η. Κ., J r . , Macromolecules, 1969,2,488. (a) Boyesso, B., Nakase, Y., and Sunner, S., Acta, Chem. Scand., 1966, 20, 803; (b) Mansson, Μ., Nakase, Y., and Sunner, S., Acta. Chem. Scand., 1968, 22, 171. Lueck, C. Η., Beste, L. F., and H a l l , H. K., J r . , J . Phys. Chem., 1963, 67, 972. H a l l , H. K., J r . , J . Org. Chem., 1964, 29, 3539. Beste, L. F., and H a l l , H. K., J r . , J . Phys. Chem., 1964, 68, 269. B i g d e l i , C. E. 493. Eisenbach, C. D., and Lenz, R. W., Macromolecules, 1976, 9, 227. Sundet, S. Α., Thamm, R. C., Meyer, J . Μ., Buck, W. Η., Caywood, S. W., Subramanian, P. Μ., and Anderson, B. C., Macromolecules, 1976, 9, 371. Sharkey, W. H., Proceedings of China-U.S. B i l a t e r a l Symposium on Polymer Chemistry and Physics, Oct. 5-10, 1979, Beijing, China, Science Press, Beijing, China, 1981, pp. 278. Oosterhoff, Η. Α., Polymer, 1974, 15, 49. Cornibert and Marchessault, Macromolecules, 1975,8,296. Lenz, R. W., Dror, M., Jorgensen, R., and Marchessault, R. Η., Polymer Engineering and Science, 1978, 18, 937. Sundet, S. Α., Macromolecules, 1978,11,146. Caywood, S. W., Rubber Chemistry and Technology, 1977, 50, 127. Thamm R. C., and Buck, W. Η., Polym. Prepr., Am. Chem. Soc., Div. Polym. Chem., 1976, 17(1), 205. Thamm, R. C., Buck, W. Η., Caywood, S. W., Meyer, J . M., and Anderson, B. C., Angew. Macromol. Chem., 1977, 58/59, 345. Calhoun G. J . , and Hewett, W. Α., U. S. Patent 3,052,657 (1960) (to Shell O i l Company). F o s s , R. P., Jacobson, D.K., Cripps, H.N., and Sharkey, W. H., Macromolecules, 1976, 9, 373. Foss, R. P., Jacobson, H. W., Cripps, Μ. Ν., and Sharkey, W. H., Macromolecules, 1979, 12, 1210. Foss, R. P., Jacobson, H. W., and Sharkey, W. H., Macro­ molecules, 1977, 10, 287. Harris, J . F. J r . , and Sharkey, W. H., Macromolecules, 1977, 10, 503. Foss, R. P., Harris, J . F. J r . , and Sharkey, W. H., Polymer Science and Technology, 1977, 10, 159.

RECEIVED April 18, 1985

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

Author Index Aida, Takuzo, 137 Aikins, James Α., 335 A r d i l l , Harriet E., 275 Bailey, William J . , 47 Bero, M., 205 Bioul, J . P., 97 Boileau, Sylvie Bouquet, G. Conde, P., C r i v e l l o , J . V., 195 Druet, J . , 97 Eckhaut, G., 219 Franta, Ε., 183 Goethals, E. J . , 219 Greene, Ruth M. E., 275 H a l l , H. K., J r . , 313 Hamilton, James G., 275 Harwood, H. James, 67 Heusehen, J . , 97 Ho, H. Thoi, 275 Hseih, H. L., 161 Hvilsted, S^ren, 105 Inoue, Shohei, 137 Ivin, Kenneth J . , 275 J e d l i i i s k i , Z. J . , 205 Jerome, R., 97 Johns, Douglas Β., 105 Kasperczyk, J . , 205 Kawakami, Yuhsuke, 245 Kobayashi, Shiro, 293 Kowalczuk, Μ., 205 Kubisa, Przemyslaw, 117

Lapienie, Grzegorz, 275 Lenz, Robert W., 105 L i t t , M. H., 231. Matyjaezeweki, Krzysztof, 117 McCann, G. Malachy, 275 McGrath, James E., 1,147

Okamoto, Yoshihisa, 361 Ouhadi, T., 97 Padias, Anne Buyle, 313 Penczek, Stanislaw, 117 Quirk, Roderic P., 37 Reibel, L., 183 Richards, D. H., 87 Robins, J . , 263 Rooney, John J . , 275 Seung, Norman S., 37 Sharkey, William H., 373 Sïomkowski, Stanislaw, 117 Sormani, P. Μ., 147 Swamikannu, X., 231 Szymanski, Ryszard, 313 Teyssie, P., 97 Van de Velde, Μ., 219 Wang, I. W., 161 Warin, R., 97 Williams, Ffrançon, 335 Wu, Meiyan, 175 Yamashita, Yuya, 245 Young, C , 263

Subject Index

A Activated monomer mechanism analogy with anionic polymerization of lactam mechanism, 76-77 contradictory evidence, 71-78,81-82 description, 71 i n i t i a t i o n step, 71,74 monomer consumption, 75 polymer chain generation, 75,81-82 propagation step, 72-75

rate of i n i t i a t i o n , 74 r a t i o of rate of monomer consumption to rate of polymer chain generation, 75,76t r a t i o of rate of monomer consumption to rate of polymer chain generation vs. conversion plot, 78,79f,80f,81 role of self-condensation reactions, 78,81

389 In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

Author Index Aida, Takuzo, 137 Aikins, James Α., 335 A r d i l l , Harriet E., 275 Bailey, William J . , 47 Bero, M., 205 Bioul, J . P., 97 Boileau, Sylvie Bouquet, G. Conde, P., C r i v e l l o , J . V., 195 Druet, J . , 97 Eckhaut, G., 219 Franta, Ε., 183 Goethals, E. J . , 219 Greene, Ruth M. E., 275 H a l l , H. K., J r . , 313 Hamilton, James G., 275 Harwood, H. James, 67 Heusehen, J . , 97 Ho, H. Thoi, 275 Hseih, H. L., 161 Hvilsted, S^ren, 105 Inoue, Shohei, 137 Ivin, Kenneth J . , 275 J e d l i i i s k i , Z. J . , 205 Jerome, R., 97 Johns, Douglas Β., 105 Kasperczyk, J . , 205 Kawakami, Yuhsuke, 245 Kobayashi, Shiro, 293 Kowalczuk, Μ., 205 Kubisa, Przemyslaw, 117

Lapienie, Grzegorz, 275 Lenz, Robert W., 105 L i t t , M. H., 231. Matyjaezeweki, Krzysztof, 117 McCann, G. Malachy, 275 McGrath, James E., 1,147

Okamoto, Yoshihisa, 361 Ouhadi, T., 97 Padias, Anne Buyle, 313 Penczek, Stanislaw, 117 Quirk, Roderic P., 37 Reibel, L., 183 Richards, D. H., 87 Robins, J . , 263 Rooney, John J . , 275 Seung, Norman S., 37 Sharkey, William H., 373 Sïomkowski, Stanislaw, 117 Sormani, P. Μ., 147 Swamikannu, X., 231 Szymanski, Ryszard, 313 Teyssie, P., 97 Van de Velde, Μ., 219 Wang, I. W., 161 Warin, R., 97 Williams, Ffrançon, 335 Wu, Meiyan, 175 Yamashita, Yuya, 245 Young, C , 263

Subject Index

A Activated monomer mechanism analogy with anionic polymerization of lactam mechanism, 76-77 contradictory evidence, 71-78,81-82 description, 71 i n i t i a t i o n step, 71,74 monomer consumption, 75 polymer chain generation, 75,81-82 propagation step, 72-75

rate of i n i t i a t i o n , 74 r a t i o of rate of monomer consumption to rate of polymer chain generation, 75,76t r a t i o of rate of monomer consumption to rate of polymer chain generation vs. conversion plot, 78,79f,80f,81 role of self-condensation reactions, 78,81

389 In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

390

RING-OPENING POLYMERIZATION

A c t i v a t e d monomer mechanism arguments a c i d - b a s e c o n s i d e r a t i o n s , 73-74 k i n e t i c c o n s i d e r a t i o n s , 74-76 A c t i v e s p e c i e s , t y p e s , 123 A c t i v e s p e c i e s - h e t e r o c y c l i c monomer addition r a t e c o n s t a n t s , 131,132t r e a c t i o n mechanism, 131 N - A l k y l a z i r i d i n e copolymerization alternating

Anionic polymerization a c t i v e s p e c i e s , 121-22 chemical s t r u c t u r e s o f growing s p e c i e s , 118,119t d i s s o c i a t i o n constants f o r macroion p a i r s , 124,125t,126 i s o m e r i c s p e c i e s , 121-22 p r o p a g a t i o n r a t e c o n s t a n t s , 127t s o l v e n t e f f e c t s , 128,129t Anionic polymerization of cyclosiloxanes c o p o l y m e r i z a t i o n , 225,2271,228f ,229 c r y p t a n d usage, 24 GC a n a l y s i s , 227-29 GPC a n a l y s i s , 224-25,226f,227,228f k i n e t i c s , 23-24 3 - p r o p i o l a c t o n e a d d i t i o n , 225 mechanism, 23 r e a c t i v i t y , 224-25 Anionic polymerization of s e q u e n t i a l monomer hexamethylcyclotrisiloxane a c t i v e s p e c i e s , 26 a d d i t i o n s , 224-25 conversion o f hexamethyl­ s t r u c t u r e and r e l a t i v e abundance cyclotrisiloxan t cycli o f c y c l i c o l i g o m e r s , 227t N-Alkylaziridine polymerizatio c h a r a c t e r i s t i c s , 219 r e a c t i o n s , 24,26,27f c l a s s i f i c a t i o n of aziridine p o l y m e r i z a t i o n d a t a , 24,25t monomers, 220t,221 p r e p a r a t i o n , 24 c o p o l y m e r i z a t i o n , 224 H-NMR spectrum o f c a r b o n - s u b s t i t u t e d p r o p a g a t i o n r a t e s , 26 A n i o n i c p o l y m e r i z a t i o n of lactam a z i r i d i n e , 221,223f mechanism i n f l u e n c e o f carbon a n a l o g y w i t h a c t i v a t e d monomer s u b s t i t u t i o n , 219-22,224 mechanism, 76-77 structure-reactivity r e l a t i o n s h i p , 219-22,224 i n i t i a t i o n s t e p , 76-77 N-Alkylaziridines p r o p a g a t i o n s t e p , 76-77 c o p o l y m e r i z a t i o n , 224 Anionic polymerization of p o l y m e r i z a t i o n , 224 octamethylcyclotetrasiloxane A l t e r n a t i n g epoxide c o p o l y m e r i z a t i o n comparison o f r e a c t i v i t y o f GPC p r o f i l e , 144,145f c y c l o s i l o x a n e s toward s i l a n o l a t e s , 31,32t H-NMR s p e c t r u m , 142,144,145f mechanism, 144 conversion o f octamethyl­ m o l e c u l a r w e i g h t and cyclotetrasiloxane to c y c l i c c o n v e r s i o n , 142,143f ,144t o l i g o m e r s , 29,30f,31 r e a c t i o n r a t e , 142,143f e f f e c t of cryptands, 2 Aluminum o x i d e c a t a l y z e d s t y r e n e o x i d e r a t e c o n s t a n t s o f f o r m a t i o n and polymerization propagation of c y c l i c a c t i v e c e n t e r s , 208f,209,211 o l i g o m e r s , 29,31,32t alcohol addition reaction r a t e o f p o l y m e r i z a t i o n , 29 p r o d u c t s , 209,210t r e a c t i o n , 29 13, ^C-NMR s p e c t r a o f a l c o h o l a d d i t i o n r e a c t i o n s , 208f,209 mechanism, 208f,209,211 s t e r e o c h e m i s t r y o f the ring-opening Β r e a c t i o n , 209 B a s e c a t a l y z e d p o l y merization, Aluminum p o r p h y r i n s , r e a c t i v i t y k i n e t i c s , 150 enhancement, 142 Base-catalyzed polymerization k i n e t i c s Anion t o c a t i o n t r a n s f o r m a t i o n , r a t e , 150 d e s c r i p t i o n , 89-90 s o l v e n t e f f e c t , 150 A n i o n i c epoxide p o l y m e r i z a t i o n Basic c a t a l y s t s c h a r a c t e r i z a t i o n o f molecular weights examples f o r c y c l i c s i l o x a n e p o l y m e r i z a t i o n , 149 and f u n c t i o n a l i t i e s , 10-11 p o l y m e r i z a t i o n mechanism, 149 r e a c t i o n scheme, 10 t y p e s , 149 s i d e r e a c t i o n s , 11-12

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

391

INDEX B i c y c l i c acetals acid c a t a l y s i s , 315 acid hydrolysis, 315t polymerization, 316 r e a c t i v i t y , 315t synthesis, 314-15 B i c y c l i c acetal polymerization mechanism, 317-18 polymer structure, 316-17 r e a c t i v i t y , 316 s t e r e o s p e c i f i c i t y , 317-18 B i c y c l i c ortho esters hydrolysis, 320-21 hydrolysis rates, 320t,321 polymerization, 321 structures, 319 synthesis, 318-19 B i c y c l i c ortho ester mechanism studies experimental, 329-30 hydride transfer reactions orthoformate exchange studies, 331,332t polymerization k i n e t i c studies, 330 vacuum l i n e technique, 330 B i c y c l i c ortho ester polymerization k i n e t i c control of polymer structure, 321-22 mechanism, 323-28 r e a c t i v i t y , 321 thermodynamic control of polymer structure, 323 water-soluble polymers, 322-23 Bicyclo[l.1.0]butane free r a d i c a l ring-opening polymerization, mechanism, 48 Biçycloalkene ring-opened polymers C-NMR spectrum of cis-trans polymer, 284,285f,286 cis-trans d i s t r i b u t i o n , 280-84 head-tail bias, 284 mechanism of biased systems, 287 mechanism of unbiased systems, 286-87 systems, 286-87 propagation parameters, 280-81,282-83t,284 propagation steps, 280-81 structure, 275-76 t a c t i c i t y , 287 Biçycloalkene ring-opening polymerization norbornene polymerization data, 283t,285f propagation by metal carbene complexes, 275,276 Bimetallic oxoalkoxide c a t a l y s t , structure, 163 Biodegradable addition polymers, synthesis, 60 Block copolymers, synthesis, 87,88

Block copolymers of polypivalolactone i n i t i a t o r s , 381 properties, 380-81 synthesis, 379-81 Block graft polymers of polypivalolac tone properties, 382-84 stress of decay, 383f,384 s t r e s s - s t r a i n relationship, 382,383f synthesis, 381-82,384 Block polymers, formation, 161 Block polymer synthesis ionic l i n k i n g groups, 93-94 reactions of l i v i n g anionic polymers with l i v i n g poly(tetrahydrofuran), 92-93 Block polymerization, experimental d e t a i l s , 163

C

e-Caprolactone block copolymerization comparison between o r i g i n a l and improved process, 164,167f GPC, 164,165f improved process experimental d e t a i l s , 164,166t scheme of improved process, 164,165f €-Caprolactone block terpolymers a n a l y t i c a l data, 170,172t glass and melt temperatures, 168t ,170,172t GPC, 170,171f synthesis, 170 t r a n s i t i o n behavior, 170,17lf €-Caprolactone diblock copolymers characterization, 164,168t glass and melt temperatures, 168t,170,172t LALLS/GPC data, 164,169t Mark-Houwink equations, 164 molecular weight c o r r e l a t i o n with i n t r i n s i c v i s c o s i t y , 164,167t 6-Caprolactone organolithium polymerization change i n molecular weight with conversion, 178,179-80f effect of terminating agent, 178,181f,182 experimental d e t a i l s , 176 mechanism, 178 reaction rates, 178t,180f stoichiometry and molecular weight d i s t r i b u t i o n , 176,177t Carbamate ion mechanism discussion, 82-83

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392

RING-OPENING POLYMERIZATION

Carbamate ion mechanism—Continued objections, 82 N-Carboxy anhydrides, polymerization, 67 N-Carboxy anhydride polymerization characteristics, 68 mechanisms, 67-68 Cation to anion transformation, description, 90-91 Cation to free radical transformation, description, 91,92 Cationic heterocyclic polymerization, initiation mechanism, 184 Cationic polymerization active species, 121,122 catalytic vs. radiation induced, 352,354 chemical structures of growing species, 119t,120 covalent active species, dissociation constants o pairs, 124,125t effective monomer concentration, 123-24 initiators, 195 isomeric species, 120 solvent effects, 128,1291 structure-reactivity relationship, 130-31,133 Cationic polymerization initiators properties, 195 structure, 195 Cationic ring-opening polymerization discussion, 293-311 epichlorohydrin, 362-63,366-70 Chemical structure determination of growing species anionic polymerization, 118,119t cationic polymerization, 120t,121 Compromise mechanism, description, 73 Covalent active species, reactivities, 124 Cryptâtes definition, 24 effect on anionic polymerization, 24 nomenclature, 24 structure, 24 Cryptoionic polymerization—See Pseudoionic polymerization Cumulene polymerization, examples, 102 Cyclic acetal copolymerization, hydrolysis of copolymers, 59 Cyclic acecal polymerization carbenium-oxonium equilibria, 121 characteristics, 189 gel permeation chromatography, 191,192f initiation, 189

Cyclic acetal polymerization initiation active sites, 191 initiators, 189 reaction, 189,191 Cyclic acetal sites, grafting experiments, 191t,193 Cyclic ketene acetal copolymerization, reaction mechanism, 59 Cyclic ketene acetals copolymerization, 59 free radical ring opening, 49-52 nitrogen and sulfur analogues, 52 Cyclic ketene acetal nitrogen analogue, synthesis and polymerization, 52-53 Cyclic ketene acetal sulfur analogue, synthesis and polymerization, 53 cationic ring-opening polymerization, 293,294 structures, 294 Cyclic vinyl ethers extent of ring opening, 53,57 ring-opening polymerization, 53-57 Cyclosiloxanes, anionic polymerization, 23

D Diallyldimethy1ammonium bromide polymerization, mechanism, 49 Diaryliodonium salt photolysis electron-transfer photoeensitlzation, 197 quantum yield, 196 rate, 196 reaction, 196 Diaryliodonium salts concentration vs. conversion rate, 198,200f nucleophilic anions, 196 photolysis, 196 Diethylzinc-water catalyzed styrene . oxide polymerization H-NMR spectra, 212,216f reaction mechanism, 211,212 3,9-Dimethylene-l,5,7,li­ te traoxaspiro[5.5]undecane double ring-opening mechanism, 58 synthesis, 57-58 Dioxacarbenium ion mechanism A 2 mechanism, 327-28 dioxacarbenium ion attack on monomer, 326-27 c

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

393

INDEX

Dioxacarbenium ion mechanism—Continued Epoxide copolymerization k i n e t i c studies, 325 alternating oxonium ion-carbenium ion copolymerization, I42,143f equilibrium, 325-26 aluminum porphyrin r e a c t i v i t y , 142 propagation rate constant, 325,327 reaction, 140,142 rate-determining step, 324-25 Epoxide homopolymerization reaction sequence, 324 acid dissociation ring s t r a i n , 326 equilibrium, 267,270f 1,3-Dioxolane, ring-opening reaction, 50 catalyst a c t i v i t y with different α,α-Disubstituted /3-propiolactones, epoxides, 267,269f anionic polymerization effect of solvent polarity and reactions, 106 catalyst on oxide α,α-Disubstituted β-propiolactone r e a c t i v i t y , 267,271f,272 anionic polymerization epoxlde-catalyet e q u i l i b r i a as a experimental d e t a i l s , 115 function of ion propagation rate constants and s t a b i l i t y , 267,270f activation mechanism for disulfone catalyst energies, 109,110t,113 deactivation, 272-73 propagation reaction mechanism 106 solvent effects on propagatio rates, 106 substituent effects on propagation oxide r e a c t i v i t y , 264,266f,268f rates, 106 oxide r e a c t i v i t y i n the presence of Disulfone disulfone, 264,267,268f reaction path for acid-catalyzed properties, 263 epoxy systems, 267,269f structures and a c i d i t y of types of c a t a l y t i c derivatives, 263,265t a c t i v i t y , 264,265f synthesis of derivatives, 263-64 Epoxide polymerization r e a c t i v i t y of porphinatoaluminum alkoxlde, 138 structure of porphinatoaluminum Ε alkoxide, 138 Epoxy aldehyde polymerization H-NMR spectra, 215,216f E l e c t r o p h i l i c ring-opening reaction mechanism, 215-16 polymerization—See Cationic ringreaction routes, 213-14 opening polymerization, 293 s e l e c t i v i t y , 214,215 Epichlorohydrin cationic Epoxy aldehydes, polymerization, 213 polymerization Ethyl-Of-alkyl /3-propiolactones, effect of temperature on anionic polymerization, 107 conversion, 363,366f Ethyl-Qf-alkyl 0-propiolactone experimental procedures, 370-71 anionic polymerization mechanism, 366-69 effect of monomers and i n i t i a t o r molecular weight, 363 concentration on molecular weight-conversion gelation, 109,112t relationship, 363,364f elemental analyses of molecular weight modifier polymers, 107,108t disappearance, 362-63,364f gelation, 109 nonfunctional c y c l i c oligomer molecular weight d i s t r i b u t i o n s formation, 363,365f before and after polymerization r a t e - i n i t i a t o r gelation, 109,112f,113 concentration molecular weight vs. relationship, 363,365f Epichlorohydrin cationic polymeriza­ time, 113,114t tion mechanism monomer conversion vs. c y c l i c oligomers, 368-69 time, 1 0 9 , l l l f discussion, 366 polymer melting points, 107,108t,109 i n i t i a t i o n , 366-67 polymer molecular weight, 107,108t termination and r e i n i t i a t i o n , 367-68 propagation rate transfer, 367-68 constants, 107,110t,113,114f

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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RING-OPENING POLYMERIZATION

Ethyl-û?-alkyl 0-propiolactone anionic polymerization—Continued s o l u b i l i t y , 107,108t Ethylene oxide enthalpy of polymerization, 37 lithium-based i n i t i a t o r s , 37-38

F Free radical polymerization double ring opening, 57-58 ring-opening vs. ring-closing reactions, 49,50 Free r a d i c a l ring-opening polymerization, examples, 47-49 Functional polysiloxanes e q u i l i b r a t i o n reaction catalysts, 149 synthesis, 148,149 Functional polysiloxane synthesis catalyst preparation, 152 end blockers, 148t experimental d e t a i l s , 153-54

H Heterocyclics, rate constants and b a s i c i c i e s , 130,131,132t,133

I Idelson-Blout mechanism contradictory evidence, 70 decarboxylation, 70-71 description, 69 reaction mechanism, 69-70 Ionic polymerization e l e c t r o p h i l i c polymerization, 307 nucleophilic polymerization, 308 Ionization reaction, reaction pathways, 123 2-Isobutyloxazoline, synthesis, 232

Ketene acetals chain transfer agents, 61-62 free radical addition-elimination mechanism, 61-62 Ketene dimer, ring-opening polymerization, 55-56

L

β-Lactone, ring-opening polymerization, 138 ^-Lactone polymerization, block copolymerization methods, 102 /3-Lactone ring-opening polymerization anionic ring-opening mechanism, 162 back-biting phenomenon, 162 H-NMR spectrum of equimolar reaction products, 140,14lf intermolecular t r a n e s t e r i f i c a t i o n , 162 IR spectrum of equimolar reaction products, 138,141f modes of cleavage, 138 140

H-NMR spectrum, 345 structure, 347 Limonene oxide C-NMR studies, 348,349f conversion-dose data and molecular weights, 337,338t,339 DSC measurements, 352,355f H-NMR studies, 341,343f IR spectra, 352,353f kinetic c h a r a c t e r i s t i c s , 337-39 structure, 338 Lithium-catalyzed polymerization of ethylene oxide degree of association of a l k a l i metal alkoxides, 39t experimental d e t a i l s , 38-39 H-NMR spectrum of poly( styrene-br-ethylene oxide), 40,43f promotion of lithium alkoxide dissociation, 39-40 size exclusion chromatogram of poly(styrene-b-ethylene oxide), 40,41f size exclusion chromatogram of polystyrene, 40,41f unreactivity of lithium alkoxides, 39

Macroion pairs and macroions aggregation, 126 dissociation constants, 124,125t,126 effect of solvent p o l a r i t y , 126 propagation rate constants, 127t,128

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

395

INDEX Metal carbene complex propagation mechanism, 276 r e a c t i v i t y , 277 structure, 277 Methacrylate-type oligosiloxane monomers, synthetic routes, 246,248 Methyl tosylate i n i t i a t e d polymerization degree of polymerization, 239,241 estimation of k /k , 239,241-42 GPC trace, 239,Î40f k i n e t i c parameters for 2-alkyloxazolinee, 2411,242 2-Methylene-3,4-benzotetrahydrofuran, polymerization, 56,57 2-Methylene-l,3-dioxepane, ring-opening polymerization mechanism, 51-52 2-Methylene-l,3-dioxolane, ring-opening polymerizatio mechanism, 50-51 2-Methyleneoxetane, ring-opening polymerization, 55 Molecular weight d i s t r i b u t i o n theory application to GPC trace, 237-39 bifunctional i n i t i a t o r , 236-37 Molecular weight modifier disappearance, 362-63

Ν

Oxirane polymerization—Continued chain propagation, 100-101 c o r r e l a t i o n with the aggregate structures, 101-2 i n i t i a t i o n period, 100 type of mechanism, 100 Oxirane polymerization i n i t i a t o r s , μ-οχο-bimetallic trinuclear alkoxides, 97-98 μ-Οχο-bimetallic alkoxide synthesis, thermal condensation process, 98 μ-Οχο-bimetallic alkoxides c h a r a c t e r i s t i c structural features, 98,99 synthesis, 98

l-Phenyl-3H-2,1-benzoxaphosphole ionic polymerization, 307-8 polymerization data, 300,301t ring-opening polymerization, 300 synthesis, 300 1- Phenyl-3H-2,l-benzoxaphosphole ring-opening polymerization i n i t i a t o r s , 301 k i n e t i c s , 302,303t,304-5 mechanism of propagation, 302-5 mechanismβ of thermal « polymerization, 301 P-NMR spectra, 302f pro-active species, 305 propagation rate constants, 304,305t time-conversion curves, 303f 2- Phenyl-l,3,2-dioxaphosphepane, ringopening polymerization, 310 2-Phenyl-l,3,2-dioxaphoephepane polymerization k i n e t i c s , 310-11 mechanism, 310 2-Phenyl-l,3,2-dioxaphosphorinane, polymerization, 311 4-Phenyl-2-methylene-l,3-dioxepane, ring-opening polymerization, 52 4-Phenyl-2-me thylene te trahyd ro furan, ring-opening polymerization, 54-55 2-Phenyl-l,2-oxaphospholane cationic polymerization a l k y l halide i n i t i a t e d systems, 298,299f,300 cationic polymerization, 295 i n i t i a t i o n , 295 k i n e t i c s , 296-97,298t,299-300 mechanisms, 300 1

New e l e c t r o p h i l i c ring-opening polymerization general scheme, 306 k i n e t i c analyses, 306,307t rate-determining step, 307 Nontransient catalysts d e f i n i t i o n , 150 example, 150

0

O l e f i n polymerization, 103 Open-chain ketene acetals, free r a d i c a l addition-elimination, 61 2-Oxazolinee, ring-opening polymerization, 231 Oxiranes, polymerization, 99 Oxirane polymerization active groups, 100 active s i t e s , 100-101 c a t a l y s t , 99-100

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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RING-OPENING POLYMERIZATION

2-Phenyl-l,2-oxaphospholane cationic polymerization—Continued MeOTf-inltiated system, 296f,297 P-NMR spectra with d i f f e r e n t catalysts, 296f,299f reduction, 295 2-Phenyl-l,2-oxaphosphorinane, r i n g opening polymerization, 308 2-Phenyl-l,2-thiaphospholane mechanism of e l e c t r o p h i l i c polymerization, 309 ring-opening polymerization, 308,309t,310 2-Phenyl-l,2-thlaphosphorlnane, r i n g opening polymerization, 308,309t,310 2-Phenyl-l,3,6,2-trioxaphosphocane k i n e t i c analyses, 311 ring-opening polymerization, 311 Photodegradable copolymers synthesis, 60,61 Photoinitlated cationic polymerization Broneted acid i n i t i a t i o n , 196 i n i t i a t i o n by diaryliodonium s a l t s , 196 i n i t i a t i o n by direct e l e c t r o p h i l i c attack on the monomer, 196 nucleophilic anions, 196 number of i n i t i a t i n g species, 196 reaction with nucleophiles, 197-98 Pinene oxides C-NMR studies, 348,350f,352t,352 conversion-dose data and molecular weights, 339,340t,341,342t DSC measurementβ, 352 H-NMR stud­ i e s , 341,344f,345-46,347f,348-49 IR spectra, 352,353f k i n e t i c c h a r a c t e r i s t i c s , 339,341 polymer structure, 345,347 structure, 338 Pivalolactone block copolymers, 379-84 block graft copolymers, 381-84 c h a r a c t e r i s t i c s , 378-79 molten polymer, 378-79 Pivalolactone polymerization i n i t i a t i o n , 373-74 mechanism, 375,377-78 propagation, 373-74 Pivalolactone polymerization mechanism chain transfer, 377-78 i n i t i a t i o n , 375 propagation, 375 rate constants, 375,376-77t Poly(dimethyl8iloxane)e molecular weight d i s t r i b u t i o n s , 33 synthesis, 147

Poly(ethylene glycol) d i t o s y l a t e , synthesis, 232 Polyepichlorohydrin g l y c o l effects on hydroxyl groups, 362-63t synthesis, 362 types of hydroxyl groups, 362,364f Polyepichlorohydrin polyols H-NMR spectrum, 370,371f properties, 369t,370 Poly(ethylene glycol) and poly(N-ieovaleryl ethylenimine) copolymerization conditions, 232t copolymer composition, 233,236 GPC traces, 232-33,234f,235 molecular weight d i s t r i b u t i o n theory 236

synthesis of copolymer and homopolymer, 232-33 unreacted i n i t i a t o r , 236 Polymers, s t r u c t u r a l c h a r a c t e r i s t i c s , 341,345-46,348,352 Polymerization k i n e t i c c h a r a c t e r i s t i c s , 337,339,341 pivalolactone, 373-75,377-84 Poly(organosiloxanes) properties, 147,245 s e l e c t i v i t y toward d i f f e r e n t gases, 245 Polysiloxane e q u i l i b r a t i o n reactions c a p i l l a r y GC c a l i b r a t i o n curve, 153,154,155f concentration vs. time, 154,156f disappearance rate, 157,158f HPLC c a l i b r a t i o n curve, 153,155f k vs. 1/T, 154,156f temperature effect on reaction rate, 157,158t Polysiloxane graft copolymers c h a r a c t e r i s t i c s , 246,249 contact angle measurement, 249,251,254f ESCA r e l a t i v e i n t e n s i t y , 255,257f f i l m forming, 260 film forming and surface active properties, 251,254f FTATR-IR and ESCA measurement, 249,251,255 FTATR-IR r e l a t i v e absorbance, 251,2561 FTATR-IR spectra, 255,257f gas permeation, 249 selective oxygen permeation, 258,259f,260 surface modification d u r a b i l i t y , 255,258,259f,260

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

397

INDEX Polysiloxane graft copolymers—Continued synthesis, 2456 Polysiloxane macromers characterization, 249,251 copolymer synthesis, 251,252t,253t monomer r e a c t i v i t y i n copolymerization, 251,254t synthesis, 249,250t,251 Propagation mechanism, transformation reactions, 88 Pseudoionic polymerization c a t a l y t i c systems, 122 description, 122

S

Selective bond cleavage mechanism, 323-24 Silanol oligomers, synthesis, 147 Siloxane equilibration a n a l y t i c a l techniques, 150-52 redistribution reactions, 148-51 Sodium alkoxlde catalyzed styrene oxide anionic polymerization alcohol addition reaction products, 207,210t C-NMR spectra of alcohol addition reactions, 207,208f i n i t i a t i o n and propagation mechanism, 207-8 structure of low molecular mass 1 3

R

Radiation-induced cationic polymerization chain transfer, 356 experimental, 336-37 features, 335 i n i t i a t i o n , 354-55 propagation, 354 rearrangement mechanism, 354-56 Ring-opening polymerizations anionic polymerization of epoxides, 8,10 anionic polymerization of organosiloxanes, 14-16 cationic or onlum ion i n i t i a t e d polymerization, 13-14 c e i l i n g temperature and propagation-depropagation behavior, 6 classes, 4 commercially important materials, 2-3 enthalpy and entropy values, 5-6 e q u i l i b r a t i o n reactions, 148 examples, 117 free energy vs. structure, 4-5 hydrolytic polymerization of €-caprolactam, 7-8 lactone polymerizations, 16-18 polymerization of 2-oxazolines, 18-19 propagation step, 2 structure-reactivity relationships, 117 thermodynamic considerations, 4-6 Ring-opening polymerization catalysts, aluminum porphyrins, 137 Ring-opening process, conditions, 206

anionic solvation, 128,129t,130 cationic polymerization, 128-30 dependence on ratio of r e a c t i v i t y of macroions and macroion pairs, 130 equilibrium, 129t monomer, 130 Styrene oxide, polymerization, 205 Styrene oxide polymerization effects of phenyl substituent, 206 epoxy ring-opening routes, 206 mechanism for stereoregular polymer formation, 212-13 Styrene-butadiene-caprolactone triblock terpolymer, c h a r a c t e r i s t i c s , 161 Styrene-ethylene oxide block polymers molecular weight characterization, 42t size exclusion chromatograms of poly(styrene-b-ethylene oxide-b­ et yrene) and poly(styrene-b-ethylene oxide), 42,43f solution c h a r a c t e r i s t i c s , 42,43t solution properties, 40,42 Styrene-type oligosiloxane monomers, synthetic routes, 246-47

Τ

Tacticity C-NMR spectrum of a l l - t r a n s atactic polymer, 287,288f dyad t a c c i c i t i e s , 287,289t

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.

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RING-OPENING POLYMERIZATION

Tacticity—Continued effects of catalyst i n i t i a t i o n , 290-91 t a c t i c i t y - c i s content c o r r e l a t i o n , 298-99 Tetrahydrofuran, ring-opening polymerization, 88 Tetrahydrofuran polymerization, i n i t i a t i o n , 183 poly(vinyl c h l o r i d e ) - s i l v e r salt metathetic reaction, 188 Tetrahydrofuran polymerization initiation addition, 184 e f f i c i e n c y of secondary halides, I86,187f,188 hydride abstraction, 185 influence of the leaving halide, 185-86 influence of the organic group, 186-87 k i n e t i c s , 188,190f proportion of active s i t e s vs. time, 186,187f proton elimination, 184 UV spectra of PVC, 188,190f Thermally Initiated cationic polymerization copper compound catalysts, 198,201 I n i t i a t i o n by a r y l a t i o n , 198,201-2 i n i t i a t o r s activated by elevated temperatures, 197 i n i t i a t o r s active at room temperature, 197 mechanism by diaryliodonium salts with copper catalysts, 201-2 mechanism by diaryliodonium salts with free r a d i c a l s , 203

Thermally i n i t i a t e d cationic polymerization—Continued reaction time vs. conversion rate, 198,199f tin(II) carboxylate reduction, 202 Transformation reactions anion to cation, 89-90 cation to anion, 90-91 cation to free r a d i c a l , 91-92 steps, 88 Transient catalysts d e f i n i t i o n , 149 example, 149

V

W

Wieland mechanism description, 68-69 reaction mechanism, 68-69

X

^-Xylylene dimer free radical ring-opening polymerization, mechanism, 48

Production by Hilary Kanter Indexing by Deborah H. Steiner Jacket design by Pamela Lewis Elements typeset by Hot Type Ltd., Washington, D.C. Printed and bound by Maple Press Co., York, Pa.

In Ring-Opening Polymerization; McGrath, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1985.