The Effects of Hostile Environments on Coatings and Plastics 9780841207981, 9780841210578, 0-8412-0798-4

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 Raymond Β. Seymour: Coming of Age with Polymers......Page 9
2 Degradation of Polymers in Hostile Environments......Page 17
Discussion......Page 18
Summary......Page 21
3 Effects of Radiation Environments on Plastics......Page 22
Major Chemical Effects......Page 23
Effects of Radiation on Physical Properties......Page 25
Resistance of Polymers to Radiation......Page 27
Literature Cited......Page 28
4 Thermal Analysis of Metal-Containing Polymers: Generalizations......Page 30
Generalizations......Page 31
Degradation Pathways......Page 33
Attempts to Enhance Thermal Stabilities......Page 38
Differentiation of Depolymerization Mechanisms......Page 42
Coupled Instrumentation Employing MS......Page 45
Summary......Page 47
Recommendations......Page 48
Literature Cited......Page 49
5 New Styrene-Maleic Anhydride Terpolymer Blends......Page 51
Results and Discussion......Page 52
Acknowledgment......Page 65
Literature Cited......Page 66
6 Polyphenylene Sulfide (PPS) in Harsh Environments......Page 67
Chemical Resistance......Page 68
Resistance To Automotive Fluids......Page 73
Thermal Stability......Page 77
Weatherability......Page 82
Flammability......Page 83
Radiation Resistance......Page 84
Applications......Page 85
Literature Cited......Page 86
7 Advances in High-Performance Polymers......Page 88
Polyacetals (POM)......Page 89
Polyamides......Page 90
Polycarbonates......Page 92
Polyphenylene oxide......Page 93
Polyphenylene sulfide......Page 94
Polyaryl esters......Page 95
Polyether ether ketone......Page 96
Polyimides......Page 97
Literature Cited......Page 98
Summary......Page 100
Introduction......Page 101
Monomer Preparation......Page 104
Acrylate and Extended-Chain Acrylate Synthesis12,14-16......Page 108
Known Biological Activity of the Monomers......Page 109
Polymerizations12,14,16......Page 111
Latex Syntheses14......Page 119
Derivatization of Preformed Polymers with Fungicidal Moieties......Page 123
Minimum Inhibitory Concentration Tests......Page 124
Agar Dish Accelerated Growth Tests......Page 128
Effect of UV Exposure......Page 133
"Zabel" Accelerated Growth Tests......Page 136
Conclusions......Page 137
Literature Cited......Page 138
9 Typical Uses and Durability of Various Plastics in Hostile Environments......Page 140
Design Criteria......Page 141
Fabrication......Page 143
B. Insert for Existing Carbon Steel Tube Pickling Tank(Figure 2)......Page 145
Summary......Page 147
10 Water Permeation Through Elastomers......Page 151
Discussion......Page 152
Effects of Elevated Temperature......Page 155
Effect of Mechanical Stress on Permeability......Page 159
Conclusions......Page 167
Literature Cited......Page 169
11 Polyurethane Aging in Water and Methanol Environments......Page 170
Experimental......Page 171
Chemical Analysis......Page 172
Chemical Analysis......Page 173
Conclusions......Page 187
Literature Cited......Page 188
12 Hostile Effects of Oxygenated Solvent Interaction with Type II Rigid Poly(vinyl Chloride)......Page 189
EXPERIMENTAL......Page 191
Results and Discussion......Page 193
Literature Cited......Page 199
13 Chemical and Solvent Resistance of Selected Styrene-Maleic Anhydride Copolymers......Page 200
Experimental......Page 201
Results and Discussion......Page 206
Literature Cited......Page 217
14 Effects of Ethanol/Gasoline and Methyl t-Butyl Ether/Gasoline Mixtures on Elastomers......Page 220
Experimental......Page 221
Results and Discussion......Page 223
Literature Cited......Page 255
Experimental......Page 256
Tensile Stress-Strain......Page 257
Results and Discussion......Page 259
Summary......Page 264
Literature Cited......Page 270
16 x-Ray Photoemission Spectroscopic Study of the Effect of Ozone on Various Styrene/Butadiene Copolymers......Page 272
Contact Angle Measurement and Critical Surface Energy......Page 274
XPS Study......Page 276
Literature Cited......Page 282
17 Environmental Corrosion of Polymers Causes and Main Reactions......Page 284
Mechanical corrosion of polymers by particulate matter......Page 286
Corrosion of polymers by sulfur oxides......Page 288
Corrosion of polymers by nitrogen oxides......Page 290
Photochemical smog......Page 291
Photosensitized reaction by hydrocarbons......Page 293
Free radical oxidation processes......Page 294
Oxidation processes with atomic oxygen, ozone and singlet oxygen......Page 295
Service Life of Polymeric Materials in Polluted Atmosphere......Page 296
Conclusions......Page 297
Literature Cited......Page 298
Corrosion Protection......Page 301
Comparison of SO2 Permeability with Permeabilities of Other Gases......Page 303
Literature Cited......Page 306
19 Photochemical Degradation and Biological Defacement of Polymers......Page 308
3. Multiple Internal Reflectance (MIR) Infrared Spectroscopy.......Page 312
RESULTS......Page 313
DISCUSSION......Page 317
CONCLUSION......Page 320
Literature Cited......Page 321
C......Page 322
D......Page 323
G......Page 324
K......Page 325
Ο......Page 326
Ρ......Page 327
S......Page 328
T......Page 329
Ζ......Page 330

Citation preview

Th Effect f Hostile Environments on Coatings and Plastics

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

The Effects of Hostile Environments on Coatings and Plastics David P. Garner, E D I T O R General Motors Research Laboratories

G. Allan Stahl

EDITOR

Phillips

Based on a symposium sponsored by the ACS Division of Organic Coatings and Plastics Chemistry at the 184th Meeting of the American Chemical Society, Kansas City, Missouri, September 12-17, 1982

229

ACS SYMPOSIUM SERIES

AMERICAN CHEMICAL SOCIETY WASHINGTON, D.C.

1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Library of Congress Cataloging in Publication Data

The Effects of hostile environments on coatings and plastics. (ACS symposium series, ISSN 0097-6156; 229) "Based on a symposium sponsored by the ACS Division of Organic Coatings and Plastics Chemistry at the 184th Meeting of the American Chemical Society, Kansas City, Missouri, September 12-17, 1982. Bibliography: p. Includes index. I. Plastics—Effect of environment on—Congresses. 2. Protective coatings—Effect of environment on—Congresses. I. Garner, David P., 1950. II. Stahl, G. Allan. III. American Chemical Society. Division of Organic Coatings and Plastics Chemistry. IV. Series. TA455.P5E38 1983 620.1'9232 83-9230 ISBN 0-8412-0798-4

Copyright © 1983 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each article in this volume indicates the copyright owner's consent that reprographic copies of the article 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. 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 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. PRINTED IN THE UNITED STATES OF AMERICA

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

ACS Symposium Series M. Joan Comstock, Series Editor

Advisory Board

David L . Allara

Robert Ory

Robert Baker

Geoffrey D . Parfitt

Donald D . Dollberg

Theodore Provder

Brian M . Harney

Charles N . Satterfield

W. Jeffrey Howe

Dennis Schuetzle

Herbert D. Kaesz

Davis L . Temple, Jr.

Marvin Margoshes

Charles S. Tuesday

Donald E . Moreland

C. Grant Willson

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

FOREWORD The ACS SYMPOSIU

a medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing ADVANCES IN CHEMISTRY SERIES except that in order to save time the papers are not typeset but are reproduced as they are submitted by the authors in camera-ready form. Papers are reviewed under the supervision of the Editors with the assistance of the Series Advisory Board and are selected to maintain the integrity of the symposia; however, verbatim reproductions of previously published papers are not accepted. Both reviews and reports of research are acceptable since symposia may embrace both types of presentation.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

PREFACE THE

QUESTION ARISES: " W H A T CONSTITUTES A HOSTILE ENVIRONMENT

FOR PLASTICS?" The word corrosive has long been associated with metals, and by inference, the effects of corrosives on plastics would suggest environments corrosive to metals However corrosiv environmen fo li not necessarily a harmful environmen ditions that might corrode a metal, a polymer may not be affected or may only be nominally affected. Conversely, environments that have no effect on metals can quickly destroy a plastic or deface a coating. The hostility of an environment is a function of the material. This volume is composed primarily of the expanded papers from the symposium, "The Effects of Hostile Environments on Plastics: A Symposium Held in Honor of Plastics Pioneer Raymond B. Seymour." Additional papers were included for better coverage of the overall topic. Each session of the symposium had a special theme: introduction and background, bulk properties, and surface characteristics. Our goal is to describe some degenerative conditions, to detail the way polymers fail, and to give alternative types of materials that are successful in hostile environments. We have avoided the temptation to divide the papers into convenient classes of physical (mechanical, thermal, and electrical), chemical (moisture, acids and bases, solvents, salts, and gases), atmospheric (weathering, radiation, and vacuum), and biological resistance. Although helpful, the use of these classes discourages emphasis on the basic behavior of specific materials. In this volume, the chapters have been divided into four sections. The first serves as an overview of and introduction to the effects of hostile environments on the micro- and macrostructure of polymers. The three chapters included in this section examine heat and radiation effects, and to a lesser extent, shear and solvent effects. Two chapters in the second section contain descriptions of specific commercially available polymers that perform under demanding conditions. Another chapter describes several "high-performance" plastics and gives general characteristics for each. The final chapter in this section is a comprehensive review of attempts to make polymers that "fight back" against attack by bioorganisms. ix

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

The seven chapters of the third section examine the effects of hostile envi­ ronments on bulk properties. The environments range from acids or pickling baths to water. The materials range from polyolefins to specialty block copolymers. The final chapter in this section contains recent findings about the effect of ozone on bulk properties. The final section on surface characteristics opens with a continuation of the effects of ozone. Two chapters report the consequences of atmospheric pollutants on surfaces. The final chapter discusses biological degradation on surfaces. D A V I D P. G A R N E R

General Motors Research Laboratories Warren, MI 48090 G. A L L A N S T A H L

Phillips Petroleum Company Bartlesville, OK 74004 May 13, 1983

χ

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1 Raymond Β. Seymour: Coming of Age with Polymers W. N. TINNERMAN University of St. Thomas, Houston, TX 77006

This Symposium on "The Effects of Hostile Environments on Plastics" is to honor The co-chairmen David Garner and G. A. Stahl as well as this speaker are former graduate students of Dr. Seymour. I first met Professor Seymour in the Spring of 1972, when I was discharged from the U.S. Army. I chose to study and work under the guidance of this man. He convinced me that Polymer Chemistry was a highly rewarding discipline which took in the many areas of chemistry, physics and math. He repeatedly told me and his other students, including graduate students of other faculty members (sometimes to their displeasure), of the ad­ vantages of a background in polymer chemistry. Even the sta­ tistics indicating that more than 50% of all chemists work in a polymer related area did little to attract large numbers of students to pursue research in the area of polymer chemistry at the University of Houston. This was most unfortunate, as these non-believers missed an opportunity to study and work with a vigorous, dedicated, industrious man who has experienced success in both academic and industrial careers. He has been involved in production, research, management, achieving the top rung of the ladder as President of a chemical firm. I would l i k e i n the b r i e f time a l l o t t e d to me to give you a thumbnail s k e t c h o f the person we are honoring. I t would be im­ p o s s i b l e to go i n t o d e t a i l , p a r t i c u l a r l y as I am only p e r s o n a l l y f a m i l i a r with Dr. Seymour's achievements i n the l a s t 10 y e a r s . Therefore, I have taken the l i b e r t y to e x t r a c t i n f o r m a t i o n from l e t t e r s of nomination as w e l l as seconding l e t t e r s f o r the v a r i o u s r e g i o n a l and n a t i o n a l awards Dr. Seymour has r e c e i v e d along with h i s p e r s o n a l v i t a e . P r o f e s s o r Seymour was born on 26 J u l y 1912 a t New England B a p t i s t H o s p i t a l i n Boston, Massachusetts. He was the second of four c h i l d r e n . He attended grade schools i n Lexington, 0097-6156/83/0229-0001 $06.00/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

2

Figure 1. Ray Seymour ing his first college years NH.

Massachusetts; New F i e l d s , New Hampshire and Dover, New Hampshire. He graduated from Dover High School i n the S p r i n g of 1929. He was s e l e c t e d as an Edison s c h o l l a r i n 1929, and was p e r s o n a l l y examined by Thomas Edison. He entered the U n i v e r s i t y of New Hampshire i n the F a l l of 1929, where he majored i n Chemical Engineering. At the time, he d i d n t r e a l i z e the a b b r e v i a t i o n f o r Chemical Engineering was Ch.E. r a t h e r than C E . and he ended up with a c l a s s of c i v i l engineers i n h i s f i r s t q u a r t e r , which was c o r r e c t e d i n the second q u a r t e r . He r e c e i v e d an education i n both chemistry and chemical engineering and has lead a dual l i f e as both a chemist and chemical engineer. While at the U n i v e r s i t y of New Hampshire, Raymond Seymour was under the guidance of Dr. Harold A. I d d l e s , which Dr. Seymour s t a t e s was an outstanding teacher whose q u a l i t i e s he has t r i e d to emulate. Dr. Seymour must have succeeded, because i n 1976 he was awarded the E x c e l l e n c e i n Teaching Award by the Chemical Manufacturers A s s o c i a t i o n . T h i s p r e s t i g e o u s award had a l s o been presented p r e v i o u s l y to Dr. I d d l e s . f

He r e c e i v e d h i s B.S. i n Chemical Engineering w i t h high honor i n June 1933, whereupon he was accepted as a graduate a s s i s t a n t at the Graduate School of U n i v e r s i t y of New Hampshire. He completed h i s Master of Science i n Chemistry from the U n i v e r s i t y of New Hampshire i n 1935. He entered the U n i v e r s i t y of Iowa i n the F a l l of 1935. As a member of Alpha C h i Sigma, which he j o i n e d at U n i v e r s i t y of New Hampshire, he was able to l i v e i n the Alpha Theta F r a t e r n i t y House at Iowa C i t y which was next to a dormitory f o r g i r l students. Here he met F r a n c i s Horan who he married i n September 1936. F r a n c i s and he w i l l be

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1. TINNERMAN

Raymond Β. Seymour

3

c e l e b r a t i n g t h e i r 46th anniversary t h i s month. The f i r s t o f t h e i r f o u r c h i l d r e n was born 1 month before Dr. Seymour r e c e i v e d h i s Ph.D. degree i n Chemistry i n the l a t e summer o f 1937. The i n d u s t r i a l career o f Dr. Seymour was now underway, as he had already interviewed f o r and accepted a job i n A p r i l 1937 with U n i v e r s a l O i l Products, paying $250 a month. He, F r a n c i s and t h e i r 1-month o l d son, David, drove from Iowa C i t y , Iowa t o R i v e r s i d e , I l l i n o i s i n a Model A where he was to begin h i s j o b at the U.O.P. l a b o r a t o r y . He was met by Dr. Gus E g g l o f f and t o l d there wasn't any job because the chem­ i c a l engineers and a r c h i t e c t s were on s t r i k e . As a p r o f e s s i o n a l chemist and President o f the American I n s t i t u t e o f Chemists, Dr. E g g l o f f suggested that Dr. Seymour look i n the want ads o f the Chemical Engineerin drove t o Akron, Ohio wher at Goodyear T i r e & Rubber Co. on Monday morning and was a t work i n the l a b o r a t o r y that afternoon. But because o f the depression, h i s s a l a r y was only $210 per month.

Figure 2. The Seymours—Frances, David and Ray—in 1940 on an outing in AIlent own, PA.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4

EFFECTS OF HOSTILE ENVIRONMENTS

At Goodyear, he was a research chemist, working i n the area of rubber a c c e l e r a t o r s , but he turned h i s a t t e n t i o n to the pro­ duction of copolymers of v i n y l c h l o r i d e and s y n t h e t i c rubber. A f t e r one year, he and a l l the other employees were informed that t h e i r s a l a r i e s had been reduced by 10%. A f t e r v o i c i n g h i s complaint, Dr. Seymour resigned and took a p o s i t i o n as Chief Chemist f o r A t l a s M i n e r a l Products i n Mertztown, Pennsylvania at the s a l a r y of $225 per month. He was t h e i r only chemist, de­ v e l o p i n g a product l i n e of p r o t e c t i v e coatings based on PVC, and pioneered the development of polymer concrete. One year at A t l a s M i n e r a l Products, and h i s s a l a r y was increased to $250 per month. (Thus, i t had taken him 4 years to overcome the e f f e c t of the s t r i k e at U.O.P.) But along with the r a i s e came the request to spend l e s s time on product development and more time i n management Research Group Leader a At Monsanto, Dr. Seymour worked with Dr. George Ham, Dr. Harry Szmant (Chairman o f Chemistry of U n i v e r s i t y of D e t r o i t ) , Dr. Ray Meyers (Professor of Kent State U n i v e r s i t y ) among o t h e r s .

Figure 3. Ray Seymour on the lecture circuit in 1945 in Chattanooga, TN— and he is still talking.

Figure 4. The young executive in 1948 in New Brunswick, Ν J.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1. TINNERMAN

Raymond Β. Seymour

5

While at Monsanto, he was confronted with the philosophy (which l a t e r changed) that chemists at Monsanto were not per­ mitted to p u b l i s h papers. He resigned i n 1945 to accept the p o s i t i o n as D i r e c t o r of Research at the U n i v e r s i t y of Chattanooga, at Chattanooga, Tennessee. In January 1949, he returned to A t l a s M i n e r a l Products, t h i s time as P r e s i d e n t . 1

He found that A t l a s products were those he had developed i n 1939, but the sons of the founder d i d not know the formulas or how to manufacture the m a t e r i a l . During h i s 5 years at A t l a s , Dr. Seymour was i n v o l v e d i n the development of p l a s t i c p i p e , formed and welded PVC s t r u c t u r e s , polyurethane coatings and many new concepts i n c o r r o s i o n r e s i s t a n t equipment. He l e f t A t l a s i n 1955 to become P r e s i d e n t of Loven Chemical near Los Angeles, C a l i f o r n i a . While i n C a l i f o r n i a , he was an Adjunct P r o f e s s o r at Los Angeles Trade Tech President of two chemica resigned and once again entered h i s r e a l l o v e , the f i e l d of academia. He accepted the p o s i t i o n of Chairman of the Department of Chemistry at Sul Ross U n i v e r s i t y i n A l p i n e , Texas i n 1960. He was a one man department. He taught 40 semester hours a week. C l a s s began at 6 a.m. and some ended at 10 p.m. His enthusiasm f o r s c i e n c e and education was contagious. The students seemed to enjoy i t , as they were very much above average. The Raymond B. Seymour Award i s given annually to S u l Ross outstanding chemistry student. In 1964 he accepted a p o s i t i o n as A s s o c i a t e Chairman of the Department of Chemistry and A s s o c i a t e Chairman of U n i v e r s i t y Research at the U n i v e r s i t y of Houston i n Houston, Texas. 1

Two of h i s students at S u l Ross followed him to Houston and became h i s f i r s t graduate students. They are Dr. Peter Tsang, p r e s e n t l y at Bendix Corporation, and Dr. Jose Sosa of Vulcan Chemical Company of W i c h i t a , Kansas. In 1976 he was f o r c e d to r e t i r e from the U n i v e r s i t y of Houston because of h i s age. He was made a P r o f e s s o r Emeritus, but not w i l l i n g to q u i t , he accepted a p o s i t i o n as D i s t i n g u i s h e d P r o f e s s o r i n the Coatings and Polymer Science Department at the U n i v e r s i t y of Southern M i s s i s s i p p i . He and Mrs. Seymour now have a home adjacent to the g o l f course i n H a t t i e s b u r g . Dr. Seymour's personal q u a l i t i e s are not confined to the formal classroom, i t i s found i n the research l a b o r a t o r y , i n the i n d u s t r i a l l a b o r a t o r y , i n the c o n t i n u i n g education of p r o f e s ­ s i o n a l chemists and secondary chemistry teachers, i n p r e s e n t i n g chemical education through r a d i o and t e l e v i s i o n programs, and i n h i s p a r t i c i p a t i o n i n e d u c a t i o n a l a c t i v i t i e s of the ACS and other p r o f e s s i o n a l o r g a n i z a t i o n s (such as American I n s t i t u t e of Chemists, American I n s t i t u t e of Chemical Engineers s i n c e 1945,

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

6

Figure 5. Ray Seymour lege in 1970; this time in Alpine, TX.

Charter member of Society of P l a s t i c Engineers, L i f e t i m e member of American A s s o c i a t i o n f o r the Advancement of Science, Society of the P l a s t i c s I n d u s t r y ) . Just w i t h i n the ACS (a 50-year member), he has served i n a variety of capacities : Member s i n c e 1932 Secretary Dayton S e c t i o n 1943-45 Chairman e l e c t Dayton S e c t i o n 1945 C o u n c i l o r Chattanooga S e c t i o n 1945-48 Member P r o f e s s i o n a l T r a i n i n g Committee 1946-48 Member Executive Committee Organic Coating and P l a s t i c s Committee 1948, 1975-6 Chairman E l e c t Lehigh V a l l e y S e c t i o n 1955 Chairman Permian Basin Section 1964 Councilor Southeastern Texas S e c t i o n 1976 Member Executive Committee Polymer D i v i s i o n 1974 Member P u b l i c R e l a t i o n s Committee 1973-76 Tour Speaker 1945, 1948, 1968, 1972, 1981, 1982, 1983 A b s t r a c t o r Chemical Abstracts Radio Commentator f o r Men and Molecules P a r t i c i p a n t f o r ACS TV shows Chairman Symposium a t Mexico C i t y , 1975; San F r a n c i s c o , 1976; New Orleans, 1977; Anaheim, 1977 I n v i t e d speaker at most ACS meetings Chairman N a t i o n a l Awards Committee, 1977 Member ACS Advisory Committee, Advances i n Chemistry Series 1978

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

1.

TINNERMAN

Raymond Β. Seymour

7

Chairman ACS Polymer Chemistry Syllabus Committee 1980 Co-Chairman ACS Polymer Education Resources Committee 1981 Chairman Education Committee, D i v i s i o n of Polymer Science 1982 Member Alpha Chi Sigma s i n c e 1932 Dr. Seymour has been awarded 45 patents and i s the author or co-author of 24 books and two audio courses. He has authored more than 1000 research and t e c h n i c a l a r t i c l e s and was recog­ n i z e d by Polymer News i n 1980 as the "world's best known polymer chemist". He has served as a consultant f o r some 12 or more companies and has served as a v i s i t i n g p r o f e s s o r of polymer science i n Bangladesh, India, Taiwan, Y u g o s l a v i a , Czechoslovakia, T r i n i d a d , USSR and A u s t r a l i a . Dr. Seymour has r e c e i v e awards which i n c l u d e the f o l l o w i n g : Western P l a s t i c s Award 1960 U n i v e r s i t y of Houston Teaching E x c e l l e n c e Award 1975 P l a s t i c Pioneer Award 1975 Chemical Manufacturers A s s o c i a t i o n C a t a l y s t Award 1976 American I n s t i t u t e of Chemists Honor S c r o l l i n L o u i s i a n a 1980 Inducted i n t o the Western P l a s t i c s H a l l of Fame 1981 Southern Chemists Award 1981 Society of P l a s t i c s Engineers I n t e r n a t i o n a l Education Award 1982.

Figure 6. Frances and the Chief, fam­ iliarfaces at ACS meetings, in 1982 in Kansas City, MO.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

8

EFFECTS OF HOSTILE ENVIRONMENTS

Raymond B. Seymour i s known to many f r i e n d s and a s s o c i a t e s as Ray, a P l a s t i c s Pioneer, as Dad to h i s four c h i l d r e n and by a v a r i e t y o f grandfatherly terms by h i s 10 grandchildren, but to h i s former students; i n c l u d i n g , Peter Tsang, Jose Sosa, Don Owen, Clem LaSada, Hubert A. Wood, Murray C l a r k , G. A l l a n S t a h l , David P. Garner, E a r l Johnson and me, he i s "The C h i e f " . RECEIVED June 7, 1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2 Degradation of Polymers in Hostile Environments HERMAN F. MARK Polytechnic Institute of New York, Brooklyn, NY 11201

The influences o f "hostile environment" on polymers heat, irradiation, the action of aggressiv y generally c l a s s i f i e d in:, a) changes o f the chemical character and microstructure of the individual macromolecules, and b) changes in the supermolecular structure and texture of the system. a) These changes include: decrease o f the molecular weight by chain scission which causes a r e duction of tensile strength, modulus and toughness, introduction of reactive (polar) groups which cause changes in compatibility, electrical and optical behavior, introduction o f light-absorbing groups which cause discoloration, and internal cyclization of the chains which may r e sult in hardening and decrease in toughness. b) These changes include: crosslinking between hitherto independent macromolecules; a moderate extent may have favorable consequences but too much o f it causes reduced impact strength and brittleness, additional crystallization; here again a certain degree of this change may be advantageous whereas too much may cause opacity, haze and crack formation, and release of gaseous fragments causing bubble formation and reducing strength. A few examples for p a r t i c u l a r l y drastic influences of hostile environment on polymeric systems will be discussed. I t i s a p l e a s u r e a n d a n h o n o r f o r me t o b e c o n t r i b u t i n g t o t h e p r o c e e d i n g o f a s y m p o s i u m h e l d i n h o n o r o f my g o o d f r i e n d ,

0097-6156/ 83/0229-0011 $06.00/0 ® 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Ray S e y m o u r . We f i r s t met a t G i b s o n I s l a n d some f o r t y y e a r s ago at a Gordon Research Conference. S i n c e t h e n , Ray h a s had a n i l l u s t r i o u s a n d e v e n t f u l c a r e e r ; h e has b e e n a n u n d e r s t a n d i n g e x p e r i m e n t a l c h e m i s t , a v e r y s u c c e s s f u l m a n a g e r a n d a d v i s o r t o chemi s t s , a n d now a n e x c e l l e n t e d u c a t o r o f c h e m i s t s . I t h i n k t h a t a n y o n e who has f o l l o w e d h i s c a r e e r i s a w a r e o f h i s n u m e r o u s c o n t r i b u t i o n s t o c h e m i s t r y a n d we a l l h o p e t h a t i n h i s c u r r e n t p o s i t i o n a t the U n i v e r s i t y o f Southern M i s s i s s i p p i he w i l l c o n t i n u e t o p r o m o t e o u r s c i e n c e a s w e l l a s make t h e w o r l d a b e t t e r p l a c e t o l i v e . Ray i s a t r u e g e n t l e m a n a s w e l l a s a s h i n i n g e x a m p l e f o r a fine scientist. Discussion I have been asked t o g i v e an o v e r v i e w o f the e f f e c t s o f host i l e environment on p l a s t i c s d e s t r u c t i o n of the bulk r a t h e r what i s happening t o i n d i v i d u a l m a c r o m o l e c u l e s i n h o s t i l e e n v i r o n m e n t s , a n d a l s o t o l a r g e r a s s e m b l i e s o f t h e m . The h o s t i l e environments t o be d i s c u s s e d are heat, r a d i a t i o n , mechanical s t r e s s e s and t h e p r e s e n c e o f o x y g e n i n c o m b i n a t i o n w i t h h e a t and radiation. Heat D e g r a d a t i o n . Heat i s m o l e c u l a r motion and f o r s o l i d b o d i e s may b e r e p r e s e n t e d b y w a v e s w h i c h t r a v e r s e t h e s y s t e m i n d i r e c t i o n s . Waves c a n b e v e r y c o m p l e x a n d t h e r e c a n b e i n t e r f e r e n c e p h e n o m e n a a n d f l u c t u a t i o n s a s s o c i a t e d w i t h t h e m . A s i m p l e example i s the white caps on a l a k e . White caps are the c o n s t r u c t i v e i n t e r f e r e n c e o f water waves. Each i n d i v i d u a l wave would n o t have the e n e r g y t o form a w h i t e c a p , but a c o m b i n a t i o n o f waves does y i e l d them. Thus, i t i s the c o n c e n t r a t i o n o f energy a t a g i v e n p o i n t t h a t i s i m p o r t a n t . A s i t i s i n water, s o can i t be i n a macromolecule. I t i s n o t t h e m o t i o n due t o t h e a v e r a g e t e m p e r a t u r e o f the p o l y m e r i c m a t e r i a l , but the f l u c t u a t i o n s t h a t are c r i t i c a l . I f t h e f l u c t u a t i o n s a r e f r e q u e n t and t h e r e i s a c o n c e n t r a t i o n o f energy through c o n s t r u c t i v e i n t e r f e r e n c e , then there i s a c o n c e n t r a t i o n of energy at a point along the chain that i s higher than the s t r e n g t h o f the c h a i n can s u p p o r t . In a l o n g f l e x i b l e c h a i n m o l e c u l e t h e r e a r e v a r i o u s s e g m e n t a l motions. E v e n t u a l l y a t one p o i n t t h e r e w i l l be s u c h a c o n c e n t r a t i o n o f energy that the chain breaks. Inthe simplest case, that o f p o l y e t h y l e n e ( P E ) w i t h o n l y C-C a n d C-H b o n d s , t h e d i s a s s o c i a t i o n e n e r g y f o r t h e s e bonds i s a b o u t 80 and 9 0 kcal/mol, resp e c t i v e l y . S o when t h e e n e r g y e x c e e d s t h e a m o u n t , t h e c h a i n b r e a k s , t h e two s i g m a b o n d i n g e l e c t r o n s a r e s e p a r a t e d a n d two l o n e e l e c t r o n s ( f r e e r a d i c a l s ) are formed. A v e r y p r o b a b l e r e a c t i o n would be f o r the r a d i c a l s t o recomb i n e . They are a l r e a d y i n a bonding s i t u a t i o n . Since t h a t i s occ u r r i n g i n s o l i d system (or c o n c e n t r a t e d s o l u t i o n ) , there i s a p o s s i b i l i t y o f a cage e f f e c t . That i s , a f t e r s e p a r a t i o n , the f r e e r a d i c a l s a r e h e l d i n a r e l a t i v e l y c o n f i n e d a r e a and a s a r e s u l t

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2.

MARK

Degradation of Polymers

13

recombination i s l i k e l y . This i s p a r t i c u l a r l y true i f the chains a r e r i g i d and t y p i c a l l y r i g i d c h a i n s c o n t a i n i n g c y c l i c a r o m a t i c u n i t s i n the c h a i n have h i g h heat s t a b i l i t y . Another example o f chains being held i n very r i g i d p o s i t i o n i s i n diamond. A carbonc a r b o n b o n d i n d i a m o n d i s no s t r o n g e r t h a n one i n PE o r a n y o t h e r o r g a n i c compound. But i n a diamond w i t h i t s t h r e e d i m e n s i o n a l s t r u c t u r e , when a b o n d b r e a k s t h e r e i s l i t t l e t h a t t h e r a d i c a l s c a n do b u t r e c o m b i n e . S o , e v e n a v e r y w e a k , s e n s i t i v e b o n d may be p r o t e c t e d t o some d e g r e e by a c a g e e f f e c t i f i t i s i n a s u f f i c i e n t l y r i g i d environment. On t h e o t h e r h a n d , i f t h e c h a i n s a r e f l e x i b l e l i k e PE a n d t h e temperature i s high with the segments moving around q u i t e r a p i d l y , t h e n t h e two e l e c t r o n s on t h e c h a i n e n d may become s o s e p a r a t e d t h a t i t i s u n l i k e l y t h a t they would recombine. Two f r e e r a d i c a l s a r e t h e n d o r m a n t . A r a d i c a l may p i c k up a h y d r o g e n f r o m an a d j a c e n t c h a i n and t h e r a d i c a the chains are broken, th s a m e . T h a t i s , t h e r e i s a r e d u c t i o n o f m o l e c u l a r w e i g h t (MW) b u t n o t o f w e i g h t . The n u m b e r o f c h a i n s go up a n d t h e MW o f t h e c h a i n s goes down. T h e r e i s a r e d u c t i o n i n t h e p r o p e r t i e s o f t h e m a t e r i a l , b u t a g a i n t h e t o t a l w e i g h t o f t h e s a m p l e d o e s n o t go down. What h a p p e n s t o t h e f r e e r a d i c a l s ? I f t h e y a r e on a f l e x i b l e m o l e c u l e l i k e PE w h i c h i s m o v i n g a r o u n d q u i t e r a p i d l y , t h e n t h e r e i s a h i g h p r o b a b i l i t y t h a t i t may p i c k o f f a h y d r o g e n o f i t s own c h a i n f i v e t o s e v e n c a r b o n a t o m s b a c k a l o n g t h e c h a i n . So t h e n t h e r e i s a t r a n s f e r o f t h e r a d i c a l t o a p o s i t i o n away f r o m t h e c h a i n e n d a n d a t e r m i n a t i o n o f a c t i v i t y a t a c h a i n e n d . The f r e e r a d i c a l may t h e n p i c k up a monomer a n d t h e n c o n t i n u e g r o w i n g f r o m t h e new r e a c t i v e p o s i t i o n . The n e t e f f e c t i s t h a t a s h o r t b r a n c h has b e e n f o r m e d . In p r i n c i p a l , t h i s i s s i m i l a r t o t h e w e l l known s h o r t c h a i n b r a n c h i n g o f PE when p r o d u c e d by t h e h i g h t e m p e r a t u r e h i g h p r e s s u r e m e t h o d . In t h i s c a s e , many s h o r t b r a n c h e s a r e f o r m e d . T h e r e i s a l s o a p r o b a b i l i t y t h a t t h e f r e e r a d i c a l may a t t a c k an a t o m f a r t h e r r e m o v e d a l o n g t h e same c h a i n a n d t h e n c y c l i z a t i o n may o c c u r . S o , i n t h e s i m p l e s t c a s e we may e x p e c t d e g r a d a t i o n , MW l o s s , b r a n c h i n g and c y c l i z a t i o n . Now t h i n g s g e t m o r e c o m p l i c a t e d a s s o o n a s t h e r e a r e s u b s t i t u e n t s on t h e c h a i n . A g a i n , a b o n d may be b r o k e n t h i s t i m e b e t w e e n a CH2 u n i t a n d a CHR u n i t w h e r e R i s t h e s u b s t i t u e n t . Two d i f f e r ent types o f r a d i c a l s are then formed. The CH2 r a d i c a l e n d g r o u p i s a v e r y r e a c t i v e r a d i c a l a n d s o o n w i l l p i c k up a h y d r o g e n . The CHR r a d i c a l i s m o r e s t a b l e a n d may e v e n be v e r y s t a b l e d e p e n d i n g on t h e g r o u p R. I f i t i s r e l a t i v e l y s t a b l e , t h e n i t may d i s a s s o c i a t e i n t o a monomer a n d i n i t i a t e a s t e p w i s e c h a i n d e p o l y m e r i z a t i o n . There are s e v e r a l cases where t h i s i s v e r y pronounced, part i c u l a r l y i f R i s v e r y s t a b i l i z i n g as i n t h e c a s e o f a l p h a - m e t h y l s t y r e n e . The d e g r a d a t i o n i n t h i s c a s e i s o f a d i f f e r e n t n a t u r e . The monomer i s e l i m i n a t e d a n d t h e r e f o r e t h e w e i g h t o f t h e s a m p l e g o e s down w h i l e t h e MW o f t h e i n d i v i d u a l m o l e c u l e r e m a i n s a p p r o x i -

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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m a t e l y t h e same. T a k i n g two m e a s u r e m e n t s , n a m e l y t h e w e i g h t o f t h e m a t e r i a l a n d t h e MW o f t h e c h a i n s , a l l o w s u s t o d i s t i n g u i s h b e t w e e n t h e two d e g r a d a t i o n m e c h a n i s m s o f c h a i n s c i s s i o n a n d d e p o l y m e r i z a t i o n i n t e r m s o f r e l a t i v e f r e q u e n c y o f t h e two m e c h a nisms. F o r e x a m p l e , b a s e d o n t h i s a p p r o a c h , we know t h a t p o l y ( m e t h y l m e t h a c r y l a t e ) (PMMA) c a n b e d e g r a d e d a t h i g h t e m p e r a t u r e s t o g i v e a g o o d y i e l d o f MMA m o n o m e r . A t h i r d p o s s i b i l i t y i s that the s u b s t i t u e n t r e a c t s with a n e i g h b o r i n g h y d r o g e n a n d RH i s r e l e a s e d . W h e n e v e r t h e b o n d s t r e n g t h s o f RH a r e l a r g e r t h a n t h e b o n d s t r e n g t h s o f t h e c h a i n and t h e t e m p e r a t u r e i s h i g h enough, t h i s w i l l be a n a d d i t i o n a l means o f d e c o m p o s i t i o n . A l l three types of decomposition discussed t h u s f a r a p p l y t o a s i n g l e c h a i n , and under g i v e n c o n d i t i o n s , may o c c u r s i m u l t a n e o u s l y . I f we c o n s i d e r t h a t t h e c h a i n i s one o f m a n y , t h e n when a f r e e r a d i c a l i s formed becaus system a hydrogen i s a b s t r a c t e may b e t r a n s f e r r e d t o a n o t h e r c h a i n . I f a c h a i n has m o r e t h a n one f r e e r a d i c a l a n d i f t h e c h a i n s a r e i n r a p i d m o t i o n , t h e n t h e r a d i c a l s may be s h i f t e d a l o n g t h e c h a i n and can p o s s i b l y w i n d up n e x t t o one a n o t h e r . The r a d i c a l s may t h e n c o m b i n e t o f o r m a double bond. The m a i n f e a t u r e s o f d e g r a d a t i o n f o r i n d i v i d u a l c h a i n s due to high temperature then are: chain s c i s s i o n , d e p o l y m e r i z a t i o n , b r a n c h i n g , s e l f b r a n c h i n g , s e l f c y c l i z a t i o n , removal o f a s u b s t i t u e n t , and f o r m a t i o n o f d o u b l e b o n d s . R a d i a t i o n D e g r a d a t i o n . What i f i r r a d i a t i o n o f t h e m o l e c u l e o c c u r s , and what i s t h e d i f f e r e n c e between h e a t i n g a m a t e r i a l and i r r a d i a t i n g i t ? Heat e s s e n t i a l l y works o n the v i b r a t i o n s o f atoms; i t i s uniform throughout the system. R a d i a t i o n works on the e l e c t r o n s a n d o n l y a few s i t e s w i l l a b s o r b e n e r g y . The e n e r g y i n the form o f photons does not go d i r e c t l y i n t o the v i b r a t i o n a l modes o f t h e m o l e c u l e s , b u t i n s t e a d i n t o t h e e x c i t a t i o n o f c e r t a i n o f i t s e l e c t r o n s . A l l o t h e r s i t e s r e m a i n u n e f f e c t e d . From t h e t h e o r y o f e l e c t r o n i c e x c i t a t i o n we know t h a t i f s o m e w h e r e i n a molecule an e l e c t r o n i s put i n t o an e x c i t e d s t a t e , there are three w a y s t o g e t r i d o f t h e e x c e s s e n e r g y . One i s f l u o r e s c e n c e , one i s p h o s p h o r e s c e n c e , and t h e l a s t and most i m p o r t a n t f o r t h i s d i s c u s s i o n i s t h e c a s c a d i n g down o f t h e e l e c t r o n i c e n e r g y i n t o v i b r a t i o n a l and r o t a t i o n a l e n e r g y ; e n e r g y e m b o d i e s i n t h e s e modes o f atoms can cause the b r e a k i n g o f a bond. R a d i a t i o n covers a wide range o f f r e q u e n c i e s from r a d i o t o gamma r a y s . The f r e q u e n c i e s o f r a d i a t i o n t h a t a r e m o s t h a r m f u l to polymeric systems are those from the blue p a r t o f the v i s i b l e s p e c t r u m a n d t h e n e a r u l t r a v i o l e t . The l o n g e r w a v e l e n g t h s a r e n o t e n e r g e t i c enough t o harm m o l e c u l e s and most o f t h e o t h e r p o t e n t i a l l y harmful high frequency rays are screened out by our atmosphere. H o w e v e r , a t 300 nm a n d a b o v e i n t o much r a d i a t i o n p e n e t r a t e s t h e a t m o s p h e r e and can a c t o n t h e m a t e r i a l . Here groups such a s

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

2.

MARK

Degradation of Polymers

15

C=0, C=C, a n d N=C b e g i n t o a b s o r b a n d e l e c t r o n s a r e l i f t e d i n t o h i g h e r e n e r g y l e v e l s . When t h e s e e l e c t r o n s d e c a y t o l o w e r e n e r g y s t a t e s , e n e r g y i s r e l e a s e d i n t h e f o r m o f v i b r a t i o n a l modes w h i c h may c a u s e a b o n d t o b r e a k a n d c r e a t e f r e e r a d i c a l s . A f t e r t h e r a d i c a l s a r e formed t h e y w i l l a g a i n r e a c t a s has been p r e v i o u s l y d e s c r i b e d . The o n e a d d i t i o n a l d a n g e r i s t h a t t h e e x c i t e d s t a t e may b e l o n g l i v e d , w h i c h c a u s e s a d e g r a d a t i o n a f t e r a l o n g p e r i o d of time. Mechanical Degradation. A t h i r d danger i s mechanical d e g r a d a t i o n . Any k i n d o f m e c h a n i c a l a c t i o n w h i c h c h a n g e s s u b s t a n t i a l l y t h e s h a p e o r s i z e o f a p o l y m e r i c s a m p l e has t h e p o t e n t i a l t o b r e a k s i n g l e b o n d s . The q u e s t i o n i s how f a s t d o t h e y f o r m a n d how f a s t d o t h e y d i s a p p e a r by p i c k i n g up hydrogen o r b y c y c l i z a t i o n . A n y t h i n g t h a t c u t s , g r i n d s , o r s h e a r s has t h e c a p a b i l i t y o f g e n e r a t i n g f r e e radicals. The m a s t i c a t i o n o m a s t i c a t i o n i s c h a i n s c i s s i o n a n d t h e r e d u c t i o n o f t h e a v e r a g e MW of the rubber. A n o t h e r example i n a d i f f e r e n t s y s t e m would be t h e f o l l o w i n g : S u p p o s e we h a v e a s e m i c r y s t a l 1 i n e m a t e r i a l a n d t h e r e a r e c h a i n s which connect two c r y s t a l l i n e domains o f t h a t m a t e r i a l w i t h each o t h e r . T h e r e i s no r e a s o n why t h e l e n g t h s o f t h o s e c h a i n s w h i c h a r e i n t h e amorphous a r e a between t h e c r y s t a l l i n e s i t e s h o u l d be t h e same. T h e r e w i l l a l w a y s be a d i s t r i b u t i o n o f c h a i n l e n g t h s . Then i f one keeps one c r y s t a l c o n s t a n t and moves t h e o t h e r as soon as t h e s t r e s s i s g r e a t e r t h a n t h e bond s t r e n g t h o f t h e s h o r t e s t c h a i n , a r u p t u r e o f t h i s c h a i n w i l l o c c u r . A s t h e d i s t a n c e between t h e c r y s t a l s i n c r e a s e s , more and more c h a i n s w i l l b r e a k . E v e n t u a l l y , a c r a c k w i l l f o r m w h i c h may t h e n p r o p a g a t e b y a d d i tional processes. The R u l e o f O x y g e n i n P o l y m e r D e g r a d a t i o n . A l a s t p o i n t t o c o n s i d e r i s t h a t i n most c a s e s heat o r r a d i a t i o n does not a c t a l o n e , but a c t s i n c o n j u n c t i o n w i t h o x y g e n . The a d d i t i o n a l p r o b l e m i s t h a t oxygen i s a v e r y r e a c t i v e m o l e c u l e and i f a f r e e r a d i c a l forms i n i t s presence then i t can combine i m m e d i a t e l y w i t h i t t o f o r m a d i f f e r e n t r a d i c a l . T h i s r a d i c a l may t h e n a b s t r a c t a h y d r o gen a n d f o r m a h y d r o p e r o x i d e . The h y d r o p e r o x i d e c a n t h e n d e c o m pose i n t o two r a d i c a l s and s o from t h e i n i t i a l two r a d i c a l s a t o t a l o f s i x p o s s i b l e r a d i c a l s may f o r m . T h i s e x p l a i n s t h e d a n g e r in c h a i n s c i s s i o n i n the presence o f oxygen l e a d i n g t o a c h a i n reaction. Summary So, i n e s s e n c e , a l l f o u r t y p e s o f d e g r a d a t i o n p r o c e e d through f r e e r a d i c a l r e a c t i o n s . Depending on the c o n d i t i o n s , they c a n b e r e l a t i v e l y h a r m l e s s when a c a g e e f f e c t i s p o s s i b l e o r t h e r e can be a whole sequence o f s e c o n d a r y and t e r t i a r y r e a c t i o n s which lead t o polymer d e g r a d a t i o n . RECEIVED April 11, 1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3 Effects of Radiation Environments on Plastics MALCOLM DOLE Los Gatos Meadows-M 101, Los Gatos, CA 95030

The effects of radiation i th environment plastics are discusse (1) major chemical reactions produced by ionizing radiations, electron beams or cobalt-60 gamma rays; (2) effects of the radiation on the physical properties of plastics; (3) relative sensitivity of different plastics to the environment; and (4) additives that can be incorporated into plastics to increase their resistance to radiations. R a d i a t i o n treatment of p l a s t i c s as i n the use of r a d i a t i o n f o r s t e r i l i z a t i o n of medical s u p p l i e s , may be more p r o t e c t i v e of the environment than s t e r i l i z a t i o n by heat. For example, i n the c u r i n g of rubber sheet ten times as many B t u s / k g of steam a r e r e quired than by using e l e c t r o n beams. The p o l l u t i o n of the atmosphere from burning c o a l or petroleum may be more s e r i o u s than p o l l u t i o n a r i s i n g from the production of e l e c t r o n beams (1). However, one u s u a l l y thinks of the dangers of r a d i a t i o n from nuclear reactors. In f a c t , i t was the d i s c u s s i o n of problems a r i s i n g from the e f f e c t of intense r a d i a t i o n on the w i r i n g i n s u l a t i o n w i t h i n the containment v e s s e l s of nuclear r e a c t o r s i n c l a s s i f i e d documents i n 1944 and 1945 that l e d the author during the academic year 1947-8 to begin h i s s t u d i e s of the e f f e c t of r a d i a t i o n s on the p l a s t i c polyethylene (PE). In t h i s very e a r l y work we found that when PE was exposed to the r a d i a t i o n of the heavy water p i l e of the Argonne N a t i o n a l Laboratory, the PE was o x i d i z e d to the extent of production of carbonyl groups i f the i r r a d i a t i o n s occurred i n a i r (2). We a l s o showed that u n s a t u r a t i o n was produced due to hydrogen e v o l u t i o n by observing the increase i n weight of the i r r a d i a t e d PE f i l m s when exposed to bromine vapor and a l s o the i n crease i n concentration of the t r a n s - v i n y l e n e i n f r a r e d absorption band a t 966 cm- . Most s u r p r i s i n g to us was the c r e a t i o n by the i r r a d i a t i o n of co-valent C-C bonds ( c r o s s l i n k s ) between the long - C H 2 - chains i n the s o l i d s t a t e a t room temperature. The extens i v e work done by Charlesby and co-workers has been e x c e l l e n t l y 1

1

0097-6156/83/0229-0017$06.00/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

18

described i n Charlesby's t r e a t i s e published i n 1960 C 3 ) . Although high energy r a d i a t i o n s can produce many d e l e t e r i o u s e f f e c t s , there are some b e n e f i c i a l aspects r e s u l t i n g c h i e f l y from produc­ t i o n of c r o s s l i n k s that have l e d to i n d u s t r i a l a p p l i c a t i o n s of great importance. The r a d i a t i o n environments with which we s h a l l be concerned are the intense r a d i a t i o n f i e l d s w i t h i n n u c l e a r r e a c t o r c o n t a i n ­ ment v e s s e l s , the r a d i a t i o n produced by ° C o gamma r a y s , the en­ vironment i n the neighborhood of h i g h energy e l e c t r o n beams which may c o n t a i n ozone and cosmic rays although we s h a l l not d i s c u s s the l a t t e r because the r a d i a t i o n i n t e n s i t i e s r e s u l t i n g from cos­ mic rays are very weak, e s p e c i a l l y at low a l t i t u d e s and w i t h i n b u i l d i n g s . Even commercial a i r l i n e personnel f l y i n g many hours at h i g h a l t i t u d e s do not seem to be a f f e c t e d by cosmic r a y s . 6

Major Chemical E f f e c t s We begin a l i s t i n g of chemical e f f e c t s w i t h a summary of the gases produced by i r r a d i a t i n g p l a s t i c s . Because most p l a s t i c s c o n t a i n hydrogen, we f i n d that hydrogen i s evolved on exposing the p l a s t i c s to h i g h energy r a d i a t i o n s . Table I compares the hydrogen y i e l d s f o r a number of p l a s t i c s i r r a d i a t e d i n a vacuum at room temperature; the y i e l d s expressed i n u n i t s of G-values, i . e . , G(H2) equals the molecules of hydrogen evolved per 100 e.v. of energy absorbed (4). Table I .

G-values f o r Gases Produced by

G(H )

3.9 2.7 0.022 - 0.026 1.7 0.64

G(HC£)

G(H )

2

LDPE PP PS POM PVAc

γ-Irradiation.

2

PPOx PMMA Nylon PET

6-6

1.12 0.1 0.36 0.02

PVC

13

From Table I i t i s c l e a r that p o l y s t y r e n e (PS) and p o l y e t h y l e n e t e r e p h t h a l a t e (PET) are much more r e s i s t a n t to γ-rays than p o l y ­ propylene (PP), low d e n s i t y PE (LDPE), poly(oxymethylene) (POM), p o l y ( v i n y l acetate) (PVAc), poly(propylene oxide) (PPOx), and somewhat more r e s i s t a n t than poly(methyl methacrylate) (PMMA) or 6-6 n y l o n . A very commonly used p l a s t i c , p o l y ( v i n y l c h l o r i d e ) (PVC), i s perhaps the l e a s t r e s i s t a n t of a l l the p l a s t i c s g i v i n g o f f hydrogen c h l o r i d e w i t h q u i t e a h i g h G-value when i r r a d i a t e d . To produce hydrogen from PE by i r r a d i a t i o n , i t i s necessary that the C-H bond be broken. Inasmuch as the chemical bond energy

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Effects of Radiation Environments

19

of the C-C covalent bond i s l e s s than that of the C-H bond, a t f i r s t s i g h t i t might be expected that the C-C bond i n PE would undergo s c i s s i o n more f r e q u e n t l y than the C-H bond. T h i s i s not the case, however, as the G-value f o r s c i s s i o n s G(S) i s q u i t e low, about 0.1 to 0.2 i n l i n e a r low d e n s i t y p o l y e t h y l e n e , LLDPE, as we have found r e c e n t l y (5). A l s o i n polybutadiene no c h a i n s c i s s i o n on i r r a d i a t i o n can be detected (6, 7). When the polymer chain contains carbon atoms connected t o four carbon atoms as i n p o l y ( i s o b u t y l e n e ) (PIB), o r t o three as i n PP, then c o n s i d e r a b l e chain s c i s s i o n s a r e produced by the i r r a d i a t i o n , G(S) equal t o -0.3 f o r PP (8) and -3 f o r PIB (4). As i n d i c a t e d by the data of Table I , i t could be expected that G(S) f o r PS would be q u i t e low and t h i s turns out t o be the case; G(S) equal t o 0.01 t o 0.02 (4) d e s p i t e the f a c t that i n PS every other carbon atom along the chain i s connected t o three carbon atoms. PMMA undergoes c o n s i d e r a b l e chain s c i s s i o n , G(S at room temperature. A i s t r y of PMMA i s that the i s o t a c t i c and s y n d i o t a c t i c forms of PMMA are a l s o converted t o the h e t e r o t a c t i c s t r u c t u r e (8) on i r r a d i ation. On breaking the C-H bond i n PE an a l k y l f r e e r a d i c a l of the s t r u c t u r e -CH2CHCH2- r e s u l t s . When two f r e e r a d i c a l s on n e i g h b o r i n g chains combine a C-C covalent bond c r o s s l i n k i n g the two chains i s formed. The G-value f o r c r o s s l i n k s , G(X), i s o f the order of magnitude o f 2.5 i n quenched LLDPE of d e n s i t y equal t o 0.9175 a t 25° (5). The evidence i s that the c r o s s l i n k s occur p r i m a r i l y i n the amorphous phase of the PE as w e l l as i n the amorphous s u r f a c e l a y e r s of s i n g l e c r y s t a l s o f PE. I n HDPE G(X) i s about 1.5 depending on the dose (9). The g r e a t e r the concentrat i o n of double bonds i n the polymer, the higher G(X) i s . F o r example, i n poly(butadiene) (PB) G(X) i s 5.7 f o r i r r a d i a t i o n s a t 25° i n vacuo (6). The l i b e r a t i o n of hydrogen from PE, GOH2) about 3.7 ( 9 ) , a l s o produces t r a n s - v i n y l e n e u n s a t u r a t i o n . In a d d i t i o n t o the format i o n of t h i s u n s a t u r a t i o n the r a d i a t i o n a l s o causes i t s d i s a p pearance and that of other unsaturated groups. In f a c t i n LHDPE of the Marlex type the G-value f o r the decay of the v i n y l end groups, G(-Vi) i s equal t o 9.6 (10) a t zero dose f o r i r r a d i a t i o n i n vacuo a t 35°. As the c o n c e n t r a t i o n of the v i n y l groups i s about 1000 times l e s s than that of the CH2 groups, one would have expected a f a r smaller G(-Vi) than G ( H 2 ) . But because G(-Vi) and G(H2) a r e the same order o f magnitude there must be c o n s i d e r a b l e energy t r a n s f e r along the PE chains to the v i n y l groups d u r i n g i t s irradiation. From the standpoint of the e f f e c t of r a d i a t i o n i n the e n v i r o n ment on p l a s t i c s , perhaps the most important r e a c t i o n i s that of o x i d a t i o n . By measuring the i n c r e a s e i n the i n f r a r e d a b s o r p t i o n band of the ^C=0 group a t 1725 cm" , Dole and h i s co-worker, Rose, discovered i n the very e a r l i e s t s t u d i e s (2) on PE that c o n s i d e r able o x i d a t i o n occurred f o r i r r a d i a t i o n s of t h e i r t h i n PE f i l m s 1

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

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i n a i r . Matsuo and Dole (11) measured the G-value f o r earbonyl formation, G( C=0), and found 5.0 f o r LHDPE. Dole (12) e s t i mated a value of 6.3 from s t u d i e s of Giberson (13) on a LDPE f i l m . Not only does the o x i d a t i o n occur during the i r r a d i a t i o n , but i t may continue f o r weeks a f t e r the i r r a d i a t i o n i f the a l l y l f r e e r a d i c a l s of s t r u c t u r e -CH - CHCH=CH or -CH CHCH=CHCH are not annealed out by h e a t i n g to 100° or h i g h e r a f t e r the i r r a d i a t i o n . Thus Williams working i n the author's l a b o r a t o r y (14) showed that even a f t e r s i x t y days of exposure to a i r at room temperature the o p t i c a l d e n s i t y of the earbonyl band at 1725 cm"" was s t i l l i n c r e a s i n g . O h n i s h i , et a l . , (15) have suggested mechanisms f o r two chain r e a c t i o n s by which the o x i d a t i o n can occur. One of the mechanisms leads to chain s c i s s i o n with the f i n a l products, -CH CH0 and -CH CHCH0. The l a t t e r f r e e r a d i c a l then adds oxygen and the process can continue. The other mechanism i n v o l v e s a hydrogen-ato group, which then rearrange 2

2

2

2

1

2

2

-CH -CH-C-CHCH I II HO 0 2

2

which can a l s o add oxygen and continue the process as a chain r e a c t i o n . Zhdanov, et a l . , (33) quote a G-value of 0.9 f o r the formation of peroxide m a c r o r a d i c a l s i n the i r r a d i a t i o n of p o l y (methyl methacrylate) a t 273K. I t should be emphasized that oxygen gas d i s s o l v e s only i n the amorphous regions of polymers, and can, t h e r e f o r e , o x i d i z e the m a t e r i a l only w i t h i n the amorphous phase or on the s u r f a c e . A l s o the extent of o x i d a t i o n per u n i t of r a d i a t i o n dose i s very dependent on the dose r a t e . The lower the dose r a t e the more time the oxygen has to d i f f u s e i n t o the p l a s t i c per u n i t of dose so that the net amount of o x i d a t i o n f o r the same dose i s much greater a t low r a t e s . In t h i s connection i t i s i n t e r e s t i n g to note that Dvornik and co-workers (17) have r e c e n t l y proposed a l o w - l e v e l chemical dosimeter made of 10 v o l . % chlorobenzene, 10 v o l . % ethanol i n 2,2,4-trimethylpentane u s i n g a spectrophotometrie method f o r C£ determination. T h i s should be of c o n s i d e r a b l e use i n measuring the i n t e n s i t y of i o n i z i n g r a d i a t i o n when of a l o w - l e v e l . E f f e c t s of R a d i a t i o n on P h y s i c a l P r o p e r t i e s As can be imagined the r a d i a t i o n produced c r o s s l i n k s and chain s c i s s i o n s act i n opposite d i r e c t i o n s with respect to changing the p h y s i c a l p r o p e r t i e s of p l a s t i c s . C r o s s l i n k s transform molten polyethylene from a l i q u i d i n t o an elastomer. The e l a s t o meric p r o p e r t i e s thus produced make p o s s i b l e the s o - c a l l e d "memory e f f e c t " i n which the i r r a d i a t e d PE, f o r example, when s t r e t c h e d at temperatures above i t s m e l t i n g p o i n t and then cooled

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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21

Effects of Radiation Environments

back t o room temperature while s t i l l s t r e t c h e d w i l l subsequently "remember" i t s o r i g i n a l unstretched dimensions when heated above i t s m e l t i n g p o i n t . I t w i l l then spontaneously s h r i n k back t o i t s o r i g i n a l dimensions and shape. The b e a u t i f u l t h i n g about t h i s process i s that the c r o s s l i n k s can be formed i n the s o l i d s t a t e at room temperature a f t e r the p l a s t i c has been molded i n t o any d e s i r e d shape. The r a d i a t i o n c r o s s l i n k i n g does not a f f e c t the shape of the o b j e c t being i r r a d i a t e d . In our f i r s t s t u d i e s on PE (2) i t was found that the i r r a d i a t i o n s of the heavy water p i l e completely removed the a b i l i t y of s t r i p s of PE f i l m to be c o l d drawn. In other words, the s t r e s s s t r a i n curves were s t r a i g h t up t o break. The marked change i n t h i s p h y s i c a l property was i n t e r p r e t e d i n terms of the formation of c r o s s l i n k s . T h i s explanation was confirmed by Charlesby (16) who showed that the i r r a d i a t i o n of PE made p a r t of the m a t e r i a l i n s o l u b l e because of th s t r u c t u r e s . The r a d i a t i o the p r a c t i c a l e f f e c t of i n c r e a s i n g the s t a b i l i t y of e l e c t r i c a l i n s u l a t i o n a t higher temperatures and the r a d i a t i o n treatment of such m a t e r i a l s i s of c o n s i d e r a b l e i n d u s t r i a l importance. As an example, Campbell (18) s t a t e s that aging a t h i g h temperatures i n gamma-ray r a d i a t i o n produced a c o n s i d e r a b l y longer l i f e t i m e i n a polyimide, a p o l y ( v i n y l formal) and a p o l y s i l o x a n e than thermal aging alone when compared a t the same temperature. W i l s k i and co-workers (19) have r e c e n t l y measured the u l t i m a t e t e n s i l e strength of h i g h impact p o l y s t y r e n e as a f u n c t i o n of the C O gamma ray dose i n the absence of oxygen and found i t to i n c r e a s e l i n e a r l y with dose up to 3 MGy (300 Mrad). During the i r r a d i a t i o n c r o s s l i n k s produced i n the polybutadiene phase reduced the elongat i o n a t break t o h a l f of i t s i n i t i a l value a f t e r a dose of 1.9 MGy and the impact s t r e n g t h to h a l f of i t s i n i t i a l value a f t e r a dose of 2.3 MGy. A very long ten year exposure i n a i r of the h i g h impact PS to a low gamma ray dose r a t e of 3.72 mGy/s (0.00134 Mrad/ hr) reduced the u l t i m a t e t e n s i l e strength i n s t e a d of i n c r e a s i n g i t to h a l f of i t s i n i t i a l value a f t e r a t o t a l dose of 0.9 MGy (90 Mrad). The r e d u c t i o n i n s t e a d of an i n c r e a s e i n the t e n s i l e strength r e s u l t e d , of course, from the o x i d a t i o n that occurred. Storage of the h i g h impact PS i n the dark f o r fourteen years d i d not change i t s mechanical p r o p e r t i e s . 60

Although r a d i a t i o n may r a i s e the s o f t e n i n g temperature because of the c r o s s l i n k s produced, the thermodynamic melting p o i n t i s h a r d l y changed i n PE as demonstrated by Dole and Howard (20) by means of accurate s p e c i f i c heat measurements. U l t r a h i g h mol e c u l a r weight polyethylene, UHMWPE, i s used as implantable prost h e t i c devices such as t o t a l j o i n t replacements because of i t s mechanical p r o p e r t i e s , r e s i s t a n c e to chemicals and to a b r a s i o n . I r r a d i a t i o n enhances i t s creep r e s i s t a n c e (21).

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

22 Resistance of Polymers

to R a d i a t i o n

Poly ( v i n y l c h l o r i d e ) , PVC, i s q u i t e s e n s i t i v e to r a d i a t i o n s ; the G-value f o r e v o l u t i o n of hydrogen c h l o r i d e has been d e t e r ­ mined to be 13 at 30° and 23 a t 70° (22). Shin and Paik (23) found that PVC p l a s t i c i z e d w i t h d i o c t y l p h t h a l a t e was more r e ­ s i s t a n t to r a d i a t i o n than r i g i d PVC. Campbell (18) i n h i s t a b l e comparing the r a d i a t i o n s t a b i l i t y of f i f t y - f i v e p l a s t i c s and elastomers l i s t s p o l y t e t r a f l u o r o e t h y l e n e (PTFE) as the l e a s t r e ­ sistant. In 1969 Hedvig (24) showed that f i l m s of PTFE of 0.04 mm t h i c k n e s s had t h e i r mechanical s t r e n g t h reduced from 269 to 136 kg c m and t h e i r e l o n g a t i o n a t break reduced from 129 per­ cent to 10 percent by an i r r a d i a t i o n to a dose of 10.4 Mrad i n air. W a l l and F l o r i n (25) compared the embrittlement of PTFE on i r r a d i a t i o n i n a i r with that on i r r a d i a t i o n i n a vacuum or an i n e r t atmosphere and foun absorbed dose to f a i l u r present. El-Sayed, et a l . , i n studying the r a d i a t i o n g r a f t i n g of a c r y l i c a c i d onto PTFE (26) and onto the copolymer p o l y t e t r a f l u o r e t h y l e n e - h e x a f l u o r o p r o p y l e n e (FEP) (27) found that more g r a f t i n g was obtained on FEP than on PTFE, that the FEP f i l m had a c o n s i d e r a b l y h i g h e r r a d i a t i o n r e s i s t a n c e than PTFE f i l m s and that FEP can be i r r a d i a t e d without extensive degradation. The H i t a c h i Cable Co., of Japan has a patent (28) on a mixture of 100 p a r t s PE and 5 p a r t s of an ethylene-1, 4-hexadienepropylene copo­ lymer i r r a d i a t e d with e l e c t r o n beams to 15 Mrad dose a f t e r which i t had an i n s o l u b l e g e l f r a c t i o n of 0.75 and 19 percent heat d i s ­ t o r t i o n compared to a g e l f r a c t i o n of 0.60 and a 28 percent heat d i s t o r t i o n a f t e r an e l e c t r o n beam dose of 20 Mrad i n the case of a pure PE sample (28). The method of measuring the heat d i s ­ t o r t i o n was not d e s c r i b e d i n the a b s t r a c t . -2

Inorganic f i l l e r s can sometimes improve the r a d i a t i o n r e ­ s i s t a n c e of polymers. Kuznetsov and co-workers (29) i n v e s t i ­ gated 30 PE-rubber compositions f i l l e d with carbon b l a c k and found that the g a s o l i n e r e s i s t a n c e i n c r e a s e d 20 to 40 percent on i n c r e a s i n g the dose to 7 Mrad and that the thermal s t a b i l i t y i n ­ creased up to 21 Mrad. In the case of u l t r a - o r i e n t e d h i g h den­ s i t y PE, T i n c e r , et a l . , (30) found that drawing reduced the o x i ­ d a t i o n of the sample f o r i r r a d i a t i o n i n a i r a t 80° (probably be­ cause of a reduced oxygen s o l u b i l i t y i n the drawn sample). Ad­ ding carbon b l a c k i n c r e a s e d the modulus i n i t i a l l y , but a f t e r doses i n the range of 40 to 60 Mrad, the modulus decreased r a p i d l y with dose. Carbon b l a c k d i d not a f f e c t the g e l content, but acted a n t a g o n i s t i c a l l y to a n t i o x i d a n t s i n that o x i d a t i o n was h i g h e r i n samples c o n t a i n i n g both carbon b l a c k and the a n t i o x i d a n t . Clough and G i l l e n (31, 32) s t u d i e d s e v e r a l types of polymeric i n s u l a t i o n m a t e r i a l s w i t h respect to t h e i r degradation at low dose r a t e s of Co-60 γ-rays. The experiments were performed on PE i n s u l a t i o n and carbon b l a c k f i l l e d PVC j a c k e t i n g s i m i l a r to that used i n n u c l e a r a p p l i c a t i o n s . They p o i n t out that from t e s t s of i n s u l a t i o n

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3. DOLE

Effects of Radiation Environments

23

s t a b i l i t y a t h i g h dose r a t e s c o n c l u s i o n s regarding the long term s t a b i l i t y of the i n s u l a t i o n a t low dose r a t e s should not be drawn because of the g r e a t e r degradation p e r u n i t of dose a t the low dose r a t e s as mentioned above. Conclusions I t i s evident from the above that the e f f e c t of high energy r a d i a t i o n s such as Co-60 gamma rays o r h i g h speed e l e c t r o n s on p l a s t i c s i s a very complicated subject with the p r e d i c t e d e f f e c t s depending g r e a t l y on the composition of the p l a s t i c . Neverthe­ l e s s , i t i s c l e a r that l i n e a r chains c o n t a i n i n g phenyl group s i d e chains a r e the most r e s i s t a n t p l a s t i c s t o i o n i z i n g r a d i a t i o n . P o l y t e t r a f l u o r e t h y l e n e and polymers w i t h a l i p h a t i c s i d e chains such as polypropylene and p o l y i s o b u t y l e n e a r e the l e a s t r e s i s t a n t to r a d i a t i o n . Campbel polymers most s u s c e p t i b l t e r e p h t h a l a t e as q u i t e s t a b l e , although i t does undergo e m b r i t t l e ment. The r e l a t i v e l y h i g h s t a b i l i t y o f the l a t t e r no doubt a r i s e s from the benzene r i n g i n the main c h a i n . We conclude t h a t with many options a v a i l a b l e regarding the composition of p l a s t i c s , i t i s p o s s i b l e t o design the environment of n u c l e a r r e a c t o r s so that a r a t h e r long l i f e o f the component p a r t s can be r e a l i z e d . The goal i s to have equipment that w i l l l a s t over the l i f e t i m e o f the p l a n t , p r o j e c t e d to be f o r t y y e a r s , and that w i l l withstand an estimated i n t e g r a t e d dose of 2x10 Gy (20 Mrad) (18). 5

Literature Cited

1. Mainati, R.L.; Schmidt, C.K.; Peters, R.J. Int. Conf. on Radiation Processing for Plastics and Rubber. Brighton, U.K. 1981, 14.1. 2. Dole, M. Report of Symposium IV. "Chemistry and Physics of Radiation Dosimetry." Technical Commend, Army Chemical Center, Maryland, 1950, p. 120. 3. Charlesby, A. "Atomic Radiation and Polymers"; Pergamon Press, New York, 1960. 4. Dole, Μ., Ed. "The Radiation Chemistry of Macromolecules" Academic: New York, 1973 Vol. II. 5. Basheer, R.; Dole, M. Submitted for publication. 6. Basheer, R.; Dole, M. Macromol. Chem. 1982, 183, 2141. 7. Batsberg, W.; Kramer, O. J. Chem. Phys. 1981, 74, 6507. 8. Thompson, E.V. Polym. Lett. 1965, 3, 675. 9. Kang, H.Y.; Saito, O.; Dole, M.: J. Am. Chem. Soc. 1967, 89, 1980. 10. Dole, M.; Milner, D.C.; Williams, T.F.; J. Am. Chem. Soc. 1958, 60, 1580. 11. Matsuo, H.; Dole, M. J. Phys. Chem. 1959, 63, 837.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

24

EFFECTS OF HOSTILE ENVIRONMENTS

12. Dole, M. "Advances in Radiation Chemistry"; Burton, M.; Magee, J.L., Eds. John Wiley, New York, 1974, Vol. 4, p. 307. 13. Giberson, R.C. J. Phys. Chem. 1962, 66, 463. 14. Ref. (12) p. 379. 15. Ohnishi, S.-I; Sagimoto, S.-I.; Nitta, I. J. Polymer Sci. A. 1963, 1, 605. 16. Charlesby, A. Proc. Roy Soc. (London) 1952, A215, 187. 17. Vekic, B.; Razem, D; Dvornik, I. Abstracts 5th Tihany Symposium on Radiation Chemistry 1982, p. 178. 18. Campbell, F.J. Proc. 3rd Int. Meeting on Radiation Processing 1980, 103. 19. Wilski, H.; Gaube, E.; Rosinger, S. Colloid & Polymer Sci. 1982, 260, 559. 20. Dole, M.; Howard, W.H. J. Phys. Chem. 1957, 61, 137. 21. Nusbaum, H.J.; Rose, R.M. J. Biomed. Materials Res. 1979, 13, 557. 22. Salovey, R. "The Radiatio Dole, Μ., Ed. Academic: New York 1973, Vol. II, p. 38. 23. Shin, C.S.; Paik, Y.H. Chungi Hakhoe Chi 1981, 30, 639. 24. Hedvig, P. J. Polym. Sci. PartA-1,1969, 7, 1145. 25. Wall, L.A.; Florin, R.E. J. Appl. Polym. Sci. 1959, 2, 251. 26. El-Sayed; Hegazy, Α.; Ishigaki, I.; Okamoto, J. J. Appl. Polym. Sci. 1981, 26, 3117. 27. El-Sayed; Hegazy, Α.; Ishigaki, I.; Dessouri, A.M.; Rabie, Α.; Okamoto, J. J. Appl. Polym. Sci. 1982, 27, 535. 28. Japanese patent 81 159 237, 1981; Chem. Abstr. 1982, 96, 40. 29. Belyakova, A.M.; Gusev, V.I.; Pavlii, V.G.; Kuznetsov, E.V. Komoz. Polim. Mater. 1981, 9, 44. 30. Tincer, T.; Cimen, F.; Cimen, I.; Akay, C. Abstracts Int. Conf. on Radiation Processing for Plastics and Rubber, Brighton, U.K. 1981, 33, 1. 31. Clough, R.L.; Gillen, K.T. Radiat. Phys. Chem. 1981, 18, 661. 32. Gillen, K.T.; Clough, R.L., ibid. 1981, 18, 679. 33. Zhdanov, G.S.; Millinchuk, V.K.; Khamidova, L.G. Abstracts 5th Tihany Symposium on Radiation Chemistry 1982, p. 195. RECEIVED February 4, 1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4 Thermal Analysis of Metal-Containing Polymers: Generalizations CHARLES E. CARRAHER, JR. Wright State University, Department of Chemistry, Dayton, OH 45435

The topic of thermal characterizations of inor ganic and organometalli reviewed by the author in a comprehensive review (1). The review emphasized particular findings and included a review of phosphorus-containing polymers and catenation polymers. The current chapter will emphasize general trends with respect to both instrumentation and results for metal-containing polymers with the realization that exceptions exist for most generalizations. The u s u a l thermal techniques o f thermal g r a v i m e t r i c analys i s (TG), d i f f e r e n t i a l thermal a n a l y s i s (DT), d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC), thermal mechanical a n a l y s i s (TM), t o r s i o n a l b r a i d a n a l y s i s (TB) and p y r o l y s i s gas chromatography (PGC) have been u t i l i z e d i n d e s c r i b i n g the thermal p r o p e r t i e s o f i n o r g a n i c and o r g a n o m e t a l l i c polymers. Because o f the v a r i e t y o f bonding energies present i n many m e t a l - c o n t a i n i n g polymers, " s t a b i l i t y plateaus" occur where degradation followed by TG occurs through s e v e r a l somewhat d i s t i n c t steps being seen as temperature ranges where l i t t l e or no l o s s o f weight occurs compared with s i m i l a r temperature ranges where weight l o s s i s more r a p i d . We have u t i l i z e d t h i s to advantage i n e v a l u a t i n g thermal techniques s i n c e degradation pathways may be more c l e a r l y d e f i n e d . Counter, the presence o f l o w - l y i n g f i l l e d and u n f i l l e d d - o r b i t a l s , present f o r most metals, permits a myriad o f o p t i o n a l pathways f o r thermal a c t i v a t i o n followed by e v o l u t i o n , c r o s s l i n k i n g and/or rearrangement t o occur. Elements such as phosphorus, s i l i c o n , t i n , germanium and s u l f u r form catenated polymers s i m i l a r t o carbon, but such c a t e n a t i o n does not u s u a l l y l e a d to (homo) chains g r e a t e r than t f

f f

0097-6156/ 83/0229-0025S06.00/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

26

10. F u r t h e r , such products might be expected to (and i n f a c t do) o f f e r poorer thermal s t a b i l i t i e s than carbon-based polymers s i n c e t h e i r bond energies are g e n e r a l l y s i g n i f i c a n t l y l e s s ( f o r i n s t a n c e the C-C bond energy f o r t y p i c a l hydrocarbons i s about 82 kcal/mol; S-S bond energy i s about 58, S i - S i i s 53 kcal/mol, P-P i s 48, and Sn-Sn i s 39 k c a l / m o l ) . The a l t e r n a ­ t i v e o f u t i l i z i n g heteroatom back-bones i s a t t r a c t i v e s i n c e the r e s u l t a n t bonds can e x h i b i t g r e a t e r bond energies than the C-C bond ( f o r i n s t a n c e , P-N has a bond energy o f 138 k c a l / mol; Be-0 i s 124, B-0 i s 113, S i - 0 i s 108, Si-N i s 104, B-C i s 89, and P-S i s 82, e x h i b i t i n g $ - i o n i c bond characters o f ~6 f o r B-C to 55 f o r Sn-0; many o f these bonds have π-bond c o n t r i b u t i o n s ) . The o f t e n r e l a t i v e l y high i o n i c bond character can s t r o n g l y i n f l u e n c e polymer behavior through chain and atom i n t e r a c t i o n s such as π-bond o v e r l a p s , chain s t i f f n e s s , ease o f undergoing rearrangemen associative reactions involvin In t h i s chapter macromolecules whose backbone or connective bridge c o n t a i n m e t a l - c o n t a i n i n g moieties which e x h i b i t s u f f i c i e n t covalent character so as t o possess d i r e c t i o n a l bonding w i l l be c o n s i d e r e d . Thus polymers such as polysodium a c r y l a t e w i l l be omitted s i n c e the metal i s bound through l a r g e l y i o n i c f o r c e s .

Generalizations G e n e r a l i z a t i o n s are appearing as the number o f thermally r e l a t e d s t u d i e s are i n c r e a s i n g . F o l l o w i n g i s a l i s t i n g o f these g e n e r a l trends along with a b r i e f d i s c u s s i o n . The term " c l a s s i c a l polymers" r e f e r to polymers as p o l y s t y r e n e and p o l y ­ ethylene. 1. Thermal p r o p e r t i e s are approximately independent o f molecular weight a f t e r a DP o f about t h r e e . T h i s i s unusually low i n comparison with many more c l a s s i c a l polymers where such thermal p r o p e r t i e s as Τ , Τ and thermal degradation may vary through DP»s o f 100. 2. Most thermograms show s t a b i l i t y plateaus - the r e s u l t of the presence o f s i g n i f i c a n t l y d i f f e r e n t bond energies w i t h i n the polymer backbone or s i d e c h a i n . More c l a s s i c a l polymers g e n e r a l l y do not e x h i b i t such plateaus with "complete" v o l a t i l i z ­ a t i o n o c c u r r i n g w i t h i n a few degrees a f t e r i n t i a l weight l o s s o c c u r s . Such s t a b i l i t y plateaus may be roughly d i v i d e d i n t o two c a t e g o r i e s - k i n e t i c a l l y independent plateaus which are independent o f h e a t i n g r a t e and time and k i n e t i c a l l y dependent plateaus which are dependent on both heating r a t e and time. As a crude r u l e -those plateaus which are p a r a l l e l t o the temper­ ature or time a x i s are k i n e t i c a l l y independent whereas those which slope downward are k i n e t i c a l l y dependent. In more c l a s s i ­ c a l polymers the k i n e t i c a l l y dependent behavior has been u t i l i z e d to determine such f a c t o r s as s p e c i f i c r a t e constants and r a t e s δ

m

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

CARRAHER

27

Thermal Analysis

of v o l a t i l i z a t i o n , order o f degradation and energy o f a c t i v a t i o n , but because o f seemingly g r e a t e r complexity o f organometallic polymer t h i s has thus f a r not been undertaken. 3. Organometallic polymers g e n e r a l l y undergo a darkening of c o l o r (often to a brown to black to gray) i n the 300 to 600°C range, becoming l i g h t e r (often white) about 900 to 1200°C. The c o l o r a t i o n may r e s u l t from formation o f aromatic intermedi­ a t e s . The subsequent l i g h t c o l o r corresponds to the c o l o r of the metal oxide ( i n a i r ) , normally white. 4. I n f r a r e d s p e c t r a l bands broaden f o r the residues as degradation proceeds. Some new bands form—some which are sharp i n d i c a t i n g formation of p r e f e r r e d intermediate r e s i d u e s . 5. I n i t i a l degradation i s o f t e n s i m i l a r i n a i r and under i n e r t c o n d i t i o n s c o n s i s t e n t with i n i t i a l degradation being nonoxidative. Subsequent degradation i s d i s s i m i l a r and c o n s i s ­ tent with o x i d a t i v e l y degradatio DSC appears to be a comparing degradation r o u t e s . Thus many TG thermograms appear s i m i l a r i n a i r and under an i n e r t atmosphere yet the DSC thermo­ grams are markedly d i f f e r e n t . 6. A number o f organometallic polymers undergo i n i t i a l degradation (with or without a s s o c i a t e d weight l o s s ) at r e l a ­ t i v e l y low temperatures (50 to 200°C range) but with r e t e n t i o n of major p o r t i o n s o f the organic p o r t i o n to g r e a t e r than 400°C. T h i s i s g e n e r a l l y described as the product's having poor to moderate low temperature s t a b i l i t i e s and moderate to good high temperature s t a b i l i t i e s . 7. The i n i t i a l thermally induced t r a n s i t i o n s o f t e n a f f e c t m a t e r i a l processing p r o p e r t i e s as Τ , Τ and s o l u b i l i t y and o f t e n i n v o l v e s rearrangement about fhe metal atom. T h i s i s d i s a p p o i n t i n g and p o i n t s to the o f t e n f r u i t l e s s attempts to o b t a i n o x i d a t i v e l y s t a b l e m a t e r i a l s through s h i e l d i n g the metal from o x i d a t i o n . A l t e r n a t e attempts might emphasize procedures for f i x i n g the geometry about the metal atom. Such " f i x i n g " , though, t y p i c a l l y r e s u l t s i n chain s t i f f e n i n g and subsequent poorer processing p r o p e r t i e s . The a f o r e i s a consequence o f a) o f t e n high i o n i c - c h a r a c t e r of the metal-associated bonds and b) presence o f l o w - l y i n g , a v a i l a b l e d - o r b i t a l s or other h y b r i d i z e d o r b i t a l s both p e r m i t t i n g ready arrangement about the metal atom. 8. Metal-containing moieties t y p i c a l l y a c t as chain s t i f f e n ­ ing agents i n c r e a s i n g Τ and T but decreasing s o l u b i l i t y . F l e x i b i l i t y i s imparted by the hydrocarbon p o r t i o n s . 9. There does not appear to be a d i r e c t c o r r e l a t i o n between thermal, o x i d a t i v e and h y d r o l y t i c s t a b i l i t i e s , thus products must be designed to emphasize the separate d e s i r e d property. H y d r o l y t i c s t a b i l i t y i s o f t e n inherent i n many organo­ m e t a l l i c polymers due to the hydrophobic nature o f the organic portions as long as the chains are not "wetted". For instance 11

1 1

ffl

g

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

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t i n p o l y e s t e r s are s t a b l e t o b o i l i n g water f o r a week, yet r a p i d l y degrade when d i p o l a r a p r o t i e l i q u i d s as DMSO are added. 10. Many o r g a n o m e t a l l i c polymers undergo i n i t i a l thermal degradation through s o l i d t r a n s i t i o n s without m e l t i n g . 11. While some o r g a n o m e t a l l i c polymers e x h i b i t t r u l y outstanding weight r e t e n t i o n , i t must be remembered that some­ times most o f the remaining residue i s i n o r g a n i c ( s p e c i f i c a l l y i n a i r -the metal oxide) thus care should be e x e r c i s e d when e v a l u a t i n g weight r e t e n t i o n data t o note how much i s t r u l y o r g a n i c . Thus one should be c o n t i n u a l l y aware o f the meaning o f weight r e t e n t i o n s , p a r t i c u l a r l y with metal-containing products which can o x i d i z e at lower temperatures l e a v i n g not a d e s i r e d moldable and/or f l e x i b l e product but r a t h e r a powdery metal o x i d e . Even i n an i n e r t atmosphere the m e t a l - c o n t a i n i n g moiety g e n e r a l l y i s one o f the l a s t t o v o l a t i l i z e . For i n s t a n c e , the S c h i f f base c o o r d i n a t i o (methylidynenitrilo)di-8-quinolino r e t e n t i o n t o 400 t o 500°C with only about 15-35$ weight l o s s e s , but on c o n s i d e r i n g the metal content t h i s represents 50 t o 75$ l o s s o f the organic p o r t i o n o f the polymer (2.). In f a c t , we have found that f o r the m a j o r i t y o f condensation polymers made by our group, the metal remains and i n many cases thermal degradation can be u t i l i z e d i n determining the amount o f metal present i n the o r i g i n a l polymer Q ) . 12. Most o r g a n o m e t a l l i c polymers e x h i b i t equal to b e t t e r weight r e t e n t i o n under i n e r t c o n d i t i o n s compared t o a i r . Degradation Pathways A number o f degradation mechanisms have been i d e n t i f i e d . Some o f these mechanisms are b r i e f l y d e s c r i b e d i n t h i s s e c t i o n . Rearrangement r e a c t i o n s a r e one l a r g e c l a s s o f degradation mechanisms i n c l u d i n g r e o r g a n i z a t i o n o f groups about the metal atom and r i n g formation. Inorganic monomers tend t o form s m a l l , unstrained r i n g s as i n the case o f s i l o x a n e s which t y p i c a l l y undergo extensive rearrangements a t temperatures i n excess o f 350°C, o f t e n forming c y c l i c products which may i n v o l v e an e q u i l i b r i u m between the c y c l i c product and the polymer. Gee (_3) has t r e a t e d such e q u i l i b r i u m as f o l l o w s f o r an e q u i l i b r i u m between a short c h a i n o r c y c l i c product R, a s h o r t e r chain C and a longer chain composed o f C + R, CR. C + R Ζ CR At e q u i l i b r i u m AG = 0. For spontaneous processes AG must be negative and at constant temperature TAS > ΔΗ. The e q u i l i b ­ rium constant i s Κ =

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

[1]

4.

CARRAHER

29

Thermal Analysis

and where the mixture i s mainly polymer Κ = 1/[R]

[CR] = [C]

and [2]

The e q u i l i b r i u m constant i s r e l a t e d to the standard f r e e energy change AG

0

= -RT In Κ = RT In [R]

[3]

I f [R] i s the c o n c e n t r a t i o n o f c y c l i c ringed products i n pure c y c l i c product, then AG = AG

0

- RT In [ R ]

AG = RT In [R]

the

q

ο

and

[4] [5]

In the absence o f weight f r a c t i o n o f chain polymer i n an e q u i l i b r i u m mixture. The r e l a t i o n s h i p AG = AH - TAS reduces to -R In (1-Φ) = AS - ΔΗ/Τ

[6]

Three s i t u a t i o n s are derived from t h i s e q u a t i o n . F i r s t , i f AH i s negative (exothermic r e a c t i o n ) , the polymer concentra­ t i o n , [CR], decreases as temperature i n c r e a s e s . I f AS i s a l s o negative, no polymer can e x i s t above a c e i l i n g temperature. I f AS i s p o s i t i v e or zero, polymer can e x i s t at any temperature (below which other a l t e r n a t i v e r e a c t i o n s o c c u r ) . I f AH = 0, the [CR] i s independent o f temperature and i s given by -R In (1 - Φ) = AS. I f AS i s n e g a t i v e , the polymer w i l l be unstable with respect to formation o f R. I f AH i s p o s i t i v e (endothermic), [CR] w i l l i n c r e a s e as temperature i n c r e a s e s . I f AS i s p o s i t i v e , polymer w i l l not e x i s t below a lower temperature g i v e n by Τ = ΔΗ/AS. I f S i s negative, no polymer can e x i s t r e g a r d l e s s o f temperature. Thus p r e d i c t i o n s can be made with regard t o the e f f e c t of temperature on such e q u i l i b r i u m r e a c t i o n s given determined AH and AS v a l u e s . Polyphosphazenes t y p i c a l l y are o f the f i r s t type w h i l e s u l f u r and selenium are o f the l a s t type (regarding AH v a l u e s ) . The r e a c t i o n o f Be^OiOCOCH^),. with d i a c i d c h l o r i d e s (4) g i v e s low molecular weight polymers. On heating, interchange o c c u r r e d and Be^OiOCCH^)^ could be sublimed at 110-140°C at 10" t o r r pressure f o r tne product derived from a d i p y l c h l o r i d e . The use o f t e r e p h t h a l y l c h l o r i d e appears to i n c r e a s e the s t a b i ­ l i t y o f the product such that a temperature o f 340°C was r e q u i r e d to o b t a i n sublimed b e r y l l i u m a c e t a t e . Interchange a l s o slowly occurs at room temperature. E l i m i n a t i o n can occur l e a d i n g t o the formation o f s t a b l e residues or may s i g n a l the onset o f continued, f u r t h e r dégrada-

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

30

11

11

t i o n . For uranyl p o l y e s t e r s O ) e l i m i n a t i o n o f i n n e r - c o r e waters at about 150°C t y p i c a l l y leads to the formation o f (2) accompanied by a change i n geometry about uranium from an o c t a ­ hedral bipyramide to an octahedral s t r u c t u r e ( 5 ) . Residue 2 i s s t a b l e to about 450°C ( 6 ) . P y r o l y s i s o f manganese p o l y amines (3) begins with e l i m i n a t i o n o f the p y r i d i n e moiety about 250°C. T h i s i s followed by a massive breakup o f the diamine moiety and e l i m i n a t i o n o f water (6_) without generation o f a stable, i d e n t i f i a b l e , isolatable residue.

H

H'

70-250°C

11 ο

ϋ

H

v/

H

Ν'

Μη

3°8

Η Η 1 ! • N-R-N4

Λ Η

Η

E l i m i n a t i o n r e a c t i o n s l e a d i n g to f u r t h e r degradation i s by f a r the more common type o f e l i m i n a t i o n degradation pathway. Many organometallic monomeric compounds undergo thermally induced d i s p r o p o r t i o n a t i o n . D i s p r o p o r t i o n a t i o n a l s o occurs i n metal-containing polymers. Aryloxy polyaluminum oxides(4) d i s p r o p o r t i o n a t e on heating, forming aluminum oxides ( 7 ) . OAr 1 4A1

0·)

4

unzipping pathways have been c i t e d as a p o s s i b l e i n i t i a l degradation pathway (J_). Oxidation o f the metal atom t y p i c a l l y occurs at some point during degradation processes o c c u r r i n g i n a i r (J_). Thus f o r

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

CARRAHER

Thermal Analysis

t i n polyamines, entrance o f oxygen t o the t i n atom through an a s s o c i a t i v e pathway with subsequent degradation i n v o l v i n g e v o l u t i o n o f both fragments d e r i v e d from the o r g a n i c backbone and organic groups bonded t o the t i n i s b e l i e v e d t o occur i n air O ) . R H H i l I 4Sn-N-R -N-) I R 1

R

n

°2

0 \/ • 4Sn-N-R ' / I I R H H o 2

» Sn0

o

[7 ]

2

I t i s i n t e r e s t i n g to note that there i s evidence t h a t f o r some s i t u a t i o n s o x i d a t i o n occurs away from the metal where the metal i s connected through ether" oxygens. For instance f o r a l k y l s i l i c o n e s , th about 250-350°C ( 8 ) . Thu s i t e o f o r i g i n a l o x i d a t i o n i s complex and not s e t t l e d . O x i d a t i o n o f t e n r e s u l t s i n the formation o f c r o s s l i n k i n g through oxygen b r i d g e s . Such products can be f a i r l y s t a b l e . Thus p o l y p h e n y l s i l o x a n e l o s e s 8$ o f i t s weight t o 400°, an a d d i t i o n a l 40$ t o 450°C and an a d d i t i o n 8$ t o 550°C (9). Polyv i n y l s i l o x a n e l o s e s 5$ a t 250°, an a d d i t i o n a l 12$ t o 350° and an a d d i t i o n a l 5$ t o 550°C. Such s i l a n e s a r e b e l i e v e d t o undergo o x i d a t i v e degradation i n i t i a l l y through cleavage o f the organic groups with c r o s s l i n k s formed through s i l o x a n e bonds, w i t h the new s t r u c t u r e r e s i s t i n g f u r t h e r o x i d a t i o n . When the metal i s bonded through nonoxygen bonds the r e s u l t s i n a i r a r e such that i n i t i a l degradation may i n v o l v e any number o f pathways and s i t e s and i s dependent on the p a r t i c u l a r polymer. Formation o f c r o s s l i n k s , t y p i c a l l y accompanied by e l i m i n a t i o n o f a s s o c i a t e d m o i e t i e s , i s a common occurrence and serves as the b a s i s f o r the formation o f g r a p h i t e , carbon and boronc o n t a i n i n g f i b e r s . T h i s i s p a r t i c u l a r l y true when nonaromatic double and t r i p l e bonds are present such as 7 o r where aromatic i t y can be gained through bond r e l o c a t i o n . 11

CH=C=NN=CH4

Fe

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

32

Borazole (8) undergoes a complex polycondensation above 500° y i e l d i n g H I B

H X

N

Ν 1

I

Η

ι

Η

Η a BNH h i g h l y c r o s s l i n k e d s t r u c t u r e (11) and p o l y b u t y l t i t a n a t e a l s o decomposes t o a complex, h i g h l y c r o s s l i n k e d t i t a n i a network. These networks a r e o f t e n then heated t o s e v e r a l thousand degrees f u r t h e r developing the c r o s s - l i n k e d network d leadin t m a t e r i a l s which e x h i b i and s t r e n g t h s . Degradation through attack o f the organometallic polymer by i m p u r i t i e s i s probably one o f the most prevalent modes o f polymer degradation, y e t a mode where l i t t l e has been r e p o r t e d . Extensive s t u d i e s c a r r i e d out on p o l y s i l o x a n e s show that the thermal p r o p e r t i e s are a l s o dependent on such items as chain l e n g t h , endgroup, and source ( i . e . , nature o f s y n t h e s i s ) . The l a t t e r i s r e l a t e d t o i n c l u s i o n o f i m p u r i t i e s , amount and d i s t r i b u t i o n o f c r y s t a l l i n i t y , e t c . The presence o f minute amounts o f i m p u r i t i e s can give misleading r e s u l t s with respect to most p h y s i c a l and chemical p r o p e r t i e s i n c l u d i n g thermal stability. The chemical and p h y s i c a l , i n c l u d i n g thermal, r e s i s t a n c e to degradation o f p o l y s i l o x a n e s i s a consequence o f both the high Si-0 bond energy (106 kcal/mol) and the r e l a t i v e l y l a r g e amount o f i o n i c character w i t h i n the Si-0 moiety. The i o n i c character o f the Si-0 bond a l s o f a c i l i t a t e s acid-and base-cata­ l y z e d rearrangement and/or degradation r e a c t i o n s . Thus h i g h l y p u r i f i e d polymethyl s i l o x a n e s a r e s t a b l e t o 350-400°C where s i l o x a n e bond interchange t o form c y c l i c products occurs ( 1 2 ) . Yet i n the presence o f s u l f u r i c acd, s i l i c o n e rubber degrades at room temperature ( 13) « Thus the presence o f t r a c e amounts o f n u c l e o p h i l i c or e l e c t r o p h i l i c agents can lead t o a dramatic decrease i n the thermal s t a b i l i t y o f organometallic polymers. T h i s becomes i n c r e a s i n g l y important when i t i s remembered that many polymeri­ zations employ such reagents as c a t a l y s t i c agents and even l e s s recognized i s the presence o f such i m p u r i t i e s i n the mono­ mers themselves. One o f the most s e r i o u s problems f a c i n g polymer s c i e n t i s t s i s the e l i m i n a t i o n o f t r a c e amounts o f water. T h i s i s p a r t i c u ­ l a r l y true with metal c o n t a i n i n g polymers which a r e p a r t i c u l a r l y s u s c e p t i b l e to h y d r o l y s i s . F o r many organometallic polymers, s t a b i l i t y t o water r e s u l t s from the hydrophobic nature o f the

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4. CARRAHER

33

Thermal Analysis

organic p o r t i o n s . As p r e v i o u s l y noted, r a p i d h y d r o l y s i s occurs when the polymers are wetted by a d d i t i o n o f l i q u i d s which are compatible with the e l e c t r o n i c nature o f the polymer c h a i n . The a c t i v a t i o n energy f o r p e n e t r a t i o n o f the "organic s h i e l d " by water i s not l a r g e and t y p i c a l l y achieved below 200°C f o r most organometallic polymers and such degradation may be respons i b l e f o r the small amount o f degradation o c c u r r i n g below 200°C observed f o r many organometallic polymers. Counter t o t h i s , we have observed that the thermal s t a b i l i t i e s o f many condensat i o n organometallic polymers i s independent o f the mode o f s y n t h e s i s ( i . e . employing aqueous present and f r e e r e a c t i o n s y n t h e t i c systems). Even so, we have not r i g o r o u s l y kept the polymer from the a i r so that water may be a t t r a c t e d t o the s u r f a c e o f the polymers. T h i s area should be studied f u r t h e r . Thus there e x i s t s a v a r i e t y o f i n i t i a l degradation pathways. Further, i t i s possibl simultaneously. More in-depth s t u d i e s should be h e l p f u l i n i d e n t i f y i n g the l e a s t s t a b l e s i t e ( s ) a l l o w i n g m o d i f i c a t i o n o f these polymers at that s i t e . Thus metal p o l y e s t e r s derived from 1,1'-diearboxyferrocene g e n e r a l l y degrade i n a i r at about 250°C. The degradat i o n begins with a s p l i t t i n g out o f C 0 and the ferrocene moiety. The degradation i s r a p i d , p o s s i b l y e x p l o s i v e , with as great as 70$ weight l o s s o c c u r r i n g over a 10°C range (14). The analogous polyethers t y p i c a l l y are s t a b l e t o about 300°C where a more g e n t l e degradation o c c u r s . Thus replacement o f the e s t e r group, which r e a d i l y forms COp, f o r an ether grouping allowed f o r the s y n t h e s i s o f more thermally s t a b l e polymers. 2

Attempts t o Enhance Thermal S t a b i l i t i e s As p r e v i o u s l y noted, s i l o x a n e s undergo extensive rearrangements a t temperatures i n excess o f 350°C, o f t e n forming c y c l i c products. Because o f the s i g n i f i c a n t mechanical, chemical, and e l e c t r i c a l p r o p e r t i e s o f f e r e d by s i l o x a n e s and modified s i l o x a n e s , great e f f o r t i s s t i l l d i r e c t e d towards i n c r e a s i n g the use temperature o f such products. T h i s work i s c l o s e l y a s s o c i a t e d with s o p h i s t i c a t e d thermal a n a l y s i s systems and i s o f t e n aimed at preventing the depolymerization (reversion) reaction. One approach often employed f o r preventing r e v e r s i o n i s m o d i f i c a t i o n o f the s i l o x a n e . Several recent attempts are described below.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

34

EFFECTS OF HOSTILE ENVIRONMENTS

Reversion and r i n g formation have been p a r t i a l l y overcome through placement o f c h a i n - s t i f f e n i n g u n i t s i n the s i l i c o n e backbone. Thus l i n e a r D^-m-carborane-siloxanes (11-14) with one t o three t r i f l u o r o p r o p y l moieties per repeating u n i t ) e x h i b i t b e t t e r thermal and o x i d a t i v e s t a b i l i t y than s i l i c o n e s and f l u o r o s i l i c o n e s ( 15). I n i t i a l degradation occurs i n a i r about 300 to 350°C, almost 100° above that t y p i c a l l y experienced f o r s i l o x a n e s and f l u o r o s i l i c o n e s . The carborane-siloxanes e x h i b i t Τ 's from -50 t o 0°C (15). The carborane moiety a l s o acts t§ i n h i b i t formation o f six-membered r i n g s because o f i t s s i z e .

CH CH I

0

0 2

CH CH ι 3 1 3 4SI—CB C S i—O-Si— 10 I I I CH. CH. CH. 0

0

CH.

3

Ucarsil F

U c a r s i l Me,

11

F

12

?3

3

F

? 3

H

Si—CB H I CH. 1 Q

1 Q

j CH.

l

CH

? 3 CSi—O-Si—04-

CH, Ï 2 CSi^Si-O4 H

-fSi—CB

i

0

H

i

0

I

CH.

u c a r s i l F, 13

?3

CH.

CH

CH.

3

CH.

U c a r s i l F. 14

Thermal a n a l y s i s o f a number o f l i n e a r polycarboranesiloxane copolymers and block polymers (such as 15-17) i n c l u d i n g TG, DT, TB, and TM was made by R o l l e r and G i l l h a m (J_6). A number of p h y s i c a l t r a n s i t i o n s were reported i n c l u d i n g c r y s t a l l i z a t i o n temperature (10 to 230°C), g l a s s t r a n s i t i o n temperature (-108 to 25°C), g l a s s y - s t a t e t r a n s i t i o n temperature (-145 t o -90°C), and m e l t i n g temperature (40 t o 260°C). T h i s i s one o f the most complete s i n g l e papers on the thermal a n a l y s i s o f i n o r g a n i c polymers regarding the types o f thermal p r o p e r t i e s c i t e d . A number o f r e s u l t s were found t h a t may have otherwise gone unnoticed i n b r i e f e r s t u d i e s (16). The c y c l i z a t i o n mechanism o f degradation which occurs f o r polydimethylsiloxane i s

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

CARRAHER

Thermal Analysis

35

not o p e r a t i v e f o r polyearboranesiloxanes. At high temperatures the polyearboranesiloxanes s t i f f e n , p o s s i b l y due to c r o s s l i n k i n g . In argon the polyearboranesiloxanes g e n e r a l l y showed an i n c r e a s e i n thermal s t a b i l i t y o f about 50°C over that o f polydimethyls i l o x a n e with many being s t a b l e at 500 to 550°C. CH. CH. I 3 ι 3 - f S i — C - B H, C - S i - 0 - 4 I 10 10 J Λn

CH

CH CH. CH CH. CHL ι 3 ι 3 | 3 t 3 | 3 -{O-Si-0-Si-C-B H, - C - S i — 0 — S i — 0 — S i - 4 1 I 10 10 ι j j 0

n

3

C H

0

Λn

^

CH

3

CH

n

CH

3

CH

3

J5

CH

3

16

CH. I 3

-fÇi—0-4 CH

3

Jl Another u t i l i z e d approach f o r preventing r e v e r s i o n i n v o l v e s c r o s s l i n k i n g o f the s i l o x a n e s . For i n s t a n c e , a number o f methyl s i l i c o n e rubbers were c r o s s l i n k e d , (about 1 c r o s s l i n k per 3,000 to 20,000 u n i t s (10-21) f o r c r o s s l i n k e d products mainly composed of dimethylsiloxane; R e f s . 17 and 1J3). DSC and TM was u t i l i z e d to evaluate the thermal p r o p e r t i e s o f the products. TM was u t i l i z e d to determine c r o s s l i n k d e n s i t y along with t y p i c a l modulus p r o p e r t i e s . Both enhancement and decrease i n thermal p r o p e r t i e s were observed depending on the mode and c o n d i t i o n s of c r o s s l i n k i n g . CH. ι 3 -fSi—0-4

H

Λ 18

0

H j and -(-Si—0-4

0

i I HLC-Si—CH —CH —Si—CH 0

2

0

2

4-

2

+

3

Η

CH

' 3 2

19

20

C H

3 -4Si-CB CH

3

C H

l 0

H

1 0

3 C>4Si-^^ CH

3

21 Another approach to combat r e v e r s i o n i s the placement of the s i l o x a n e or modified s i l o x a n e on an " i n e r t " support

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

3

EFFECTS OF HOSTILE ENVIRONMENTS

36

which can a s s i s t i n maintaining the o r i g i n a l nonreverted s t r u c ­ t u r e . Thus F i n c h (19) reported the formation o f a new chromato­ graphic phase s t a b l e t o 500°C based on a polycarboranesiloxane s t a t i o n a r y phase. The system was capable o f e f f i c i e n t separa­ t i o n s from 50 to 500°C. In f a c t , TG's o f the polycarborane­ s i l o x a n e phase showed complete weight r e t e n t i o n t o about 700°C. The meta-carborane was u t i l i z e d i n t h i s study. S i l o x a n e - l a d d e r polymers have been known f o r some time. A polymer derived from p h e n y l t r i c h l o r o s i l a n e (2), w h i l e i n f u ­ s i b l e , i s s o l u b l e i n s o l v e n t s such as tetrahydrofuran and benzene from which f i l m s can be cast (20,2_p. TG thermograms i n a i r show no weight l o s s t o 525° C but an upper l i m i t f o r u s e f u l a p p l i c a t i o n i s probably near 300° C (21).

\

\

Several researchers have s u c c e s s f u l l y employed the a d d i t i o n of a n t i o x i d a n t s t o improve thermal s t a b i l i t y . Thus N a n n e l l i , Gillman and Black (22) found that the degradation o f 23 proceeds i n a i r through o x i d a t i o n and cleavage o f the organic s i d e groups with a degradation i n c e p t i o n temperature around 200°C. The gas chromatograms o f the v o l a t i l e decomposition products o f Cr[0P(CH" )(C H )0] 0P(C H ) 0 showed a t l e a s t 14 products of which 2-octane, a c e t i c a c i d , and η-butyric a c i d are among the most abundant. Decomposition does occur at 200°C f o r long exposure times with a 13$ weight l o s s f o r an 18-hour exposure time. A d d i t i o n o f a n t i o x i d a n t s such as d i s t e a r y l t h i o d i p r o p i o nate i n c r e a s e s the l o n g e v i t y o f the polymer f i l m s f l e x i b i l i t y at 200°C. 3

6

5

2

6

ο

ρ

23

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

CARRAHER

Thermal Analysis

37

D i f f e r e n t i a t i o n o f Depolymerization

Mechanisms

MacCallum (25) r e l a t e d the change i n number average mole­ c u l a r weight, DP, with depolymerization mechanism d i v i d i n g the pathways i n t o the groups c h a r a c t e r i z e d by the nature o f the i n i t i a t i o n reaction-random s c i s s i o n or end group. These groups can be f u r t h e r d i v i d e d i n t o i n i t i a l degradation followed by a) p a r t i a l unzipping and b) complete u n z i p p i n g . Polymer degradation can be described i n terms o f the weight of polymer, W, at time t , number o f molecules, N, at time t , and DP as f o l l o w s where m i s the molecular weight o f each mer unit. W = N m DP

[8]

D i f f e r e n t i a t i o n wit

m

-1 dW dt =

dDP

N

St

— +

D

P

dN dt

Γ η Ί [ 9 ]

For random i n i t i a t i o n followed by incomplete unzipping and assuming that depolymerization i s f i r s t - o r d e r with respect to sample weight g i v e s dN/dt = kW/m

and

[10]

-dW/dt = kWZ

[11]

where Ζ i s the average unzipping l e n g t h , i . e . number o f mers separated from the c h a i n . Combination o f [8]-[11] followed by i n t e g r a t i o n g i v e s s

DP/DP 0

DP

ο

( J f \C DP

C

ο

)= f (1-C)/(C+f) + Z/

[12]

where f = Z/DP"

and C, the f r a c t i o n a l conversion, i s (W -W)/W . ο ο ο For random i n i t i a l depolymerization followed by complete unzipping, Ζ can be r e l a t e d to DP through a parameter, B, t h a t i s r e l a t e d to the p o l y d i s p e r s i t y o f the polymer sample. Ζ = DP Β Combining [10], [11] and DP/DP = ( 1 - C ) Q

[13] [13] i n t o [9] with i n t e g r a t i o n g i v e s ( B

"

1 ) / B

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

[14]

38

EFFECTS OF HOSTILE ENVIRONMENTS

For chain-end

i n i t i a t i o n followed by p a r t i a l unzipping

-DN/dt = 0

[15]

and from [ 9 ] , [11] and [15] with i n t e g r a t i o n DP/DP = 1-C ο

[16]

For i n i t i a l end-group depolymerization followed by complete unzipping -dN/dt = kN

[17]

and combining [ 8 ] , [ 9 ] , [11] and [17] followed by i n t e g r a t i o n yields DP/DP

ο

=1

In a s i t u a t i o n where i n t r a m o l e c u l a r "loops" o f constant s i z e a r e formed and r a p i d l y removed (as v o l a t i l e s under reduced or ambient pressure) equations [11] and [15] apply and can be incoporated i n t o [9] g i v i n g [16] a f t e r i n t e g r a t i o n . Thus f o r end-group depolymerization, DP i s a l i n e a r f u n c t i o n of time f o r p a r t i a l unzipping and independent o f time f o r complete unzipping. F o r random bond breakage p a r t i a l unzipping i s a complicated l o g a r i t h m i c f u n c t i o n o f DP r e l a t e d t o r e a c t i o n extent whereas complete unzipping i s r e l a t e d t o a l i n e a r f u n c t i o n o f 1/DP with time. The a f o r e s i t u a t i o n can be p i c t u r e d as shown i n F i g u r e 1. L i n e A, corresponding t o i n i t i a l end-group depolymerization followed by complete unzipping shows no change i n molecular weight s i n c e the i n i t i a t i o n o f depolymerization i s the r a t e determining s t e p ; i . e . chain lengths o f remaining chains remain unchanged. Counter, i f end-group depolymerization i s followed by incomplete unzipping, C, average chain length w i l l decrease slowly, the change i n average chain l e n g t h r e l a t e d t o the s i z e of segment removed, i n c l u d i n g l o o p s . A curve such as Β r e s u l t s where random s i s s i o n i s followed by complete unzipping s i n c e there i s a r e l a t i v e l y slow decrease i n molecular weight with conversion. Random depolymerization followed by incomplete unzipping r e s u l t s i n a r a p i d decrease i n molecular weight with conversion and i s p i c t o r i a l i z e d as D. Both Β and D a r e members of a number o f s i m i l a r curves, the exact shape being dependent on the exact depolymerization parameters. These curves can be computer-generated f o r v a r y i n g s i t u a t i o n s . Degradation may i n v o l v e more than one pathway. The a f o r e approach can be extended t o consider these cases and o t h e r s . Thus f o r degradation o c c u r r i n g through formation o f v o l a t i l e loops as w e l l as through an i n t e r n a l , i n t e r m o l e c u l a r process,

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

CARRAHER

Thermal Analysis

0

F r a c t i o n o f Depolymerization

1

Figure 1. Idealized plots relating molecular weight ratio to depolymerization mechanisms. Key: A, end-group depolymerizationfollowed by complete unzipping; B, random scission followed by complete unzipping; C, end-group depolymerization followed by incomplete unzipping; and D, random depolymerization followed by incomplete unzipping. equations [8] and i s given by -dW/dt

[9] s t i l l h o l d . s kmZW =

f

kW

The r a t e o f weight l o s s [19]

The r a t e o f change o f molecular p o p u l a t i o n i n the condensed phase depends on the r e l a t i v e magnitudes o f the r a t e o f loop formation forming v o l a t i l e and n o n v o l a t i l e oligomers, e t c . These changes can be assumed to be a weak f u n c t i o n o f time as f o l l o w s where A ( t ) d e s c r i b e s the time dependence o f the p a r t i c u l a r systems. dN/dt = A ( t )

[20]

T h i s f u n c t i o n can be parametized i n a number o f ways i n c l u d i n g i n v o l v i n g i n i t i a l population, polymer l i f e t i m e and other s e a l i n g parameters. Models combining growth and decay through v a r i o u s routes can be made and computer p l o t s made with ensuing curve f i t t i n g . Thus there e x i s t s s e v e r a l ways to determine the mode o f depolymerization with most r e q u i r i n g the products to be s o l u b l e p e r m i t t i n g molecular weight to be determined. Further these approaches are best s u i t e d to s i t u a t i o n s where depolymerization occurs through a s i n g l e mechanistic pathway. Thus f o r polymers as s i l o x a n e s the a f o r e techniques should be r e a d i l y a p p l i c a b l e but f o r many metal-containing polymers degradation proceeds through the formation o f i n s o l u b l e r e s i d u e s .

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

40 Coupled Instrumentation Employing MS

PY-GC-MS and GC-MS have been e x t e n s i v e l y u t i l i z e d i n both t r a d i t i o n a l product i d e n t i f i c a t i o n and i n s e l e c t s t u d i e s t o a s s i s t i n the d e s c r i p t i o n o f the thermal degradation o f the m a t e r i a l s . These techniques t y p i c a l l y do not a l l o w a ready, s t r a i g h t f o r w a r d i n t e r p r e t a t i o n o f degradation sequences due to c o n s i d e r a b l e combination o f evolved fragments on the GC columns. In an e f f o r t t o overcome problems o f combination, we f i r s t constructed a TG-MS assembly where the evolved s p e c i e s from thermodegradation were swept, by a helium purge gas, i n a s t r a i g h t l i n e where the d i s t a n c e between the TG sample compartment (boat) and the MS i o n i z a t i o n source was about three f e e t (23). While numerous i o n fragments were found, i t was s u r p r i s i n g that c e r t a i n species s t i l l underwen groups d e r i v e d from a numbe o f biphenyl formed was i n great excess with that c a l c u l a t e d u s i n g simple gas c o l l i s i o n theory. Presumably combination i s o c c u r r i n g w i t h i n the s o l i d sample p r i o r t o e v o l u t i o n o f that fragment. Formation o f biphenyl occurred even when the samples were ground t o a f i n e powder. The TG-MS assembly c o n s i s t e d o f a double-focusing DuPont 21-491 Mass spectrometer coupled through a s i n g l e - s t a g e g l a s s j e t separator t o a DuPont 951 Thermal G r a v i m e t r i c Analyzer which was attached t o a DuPont 990 Thermal Analyzer Console. The MS was equipped with a Hewlitt-Packard, HP-2216C computer having 24K core memory and a d i s c - o r i e n t e d data system s p e c i a l l y developed f o r the DuPont 21-491 Mass Spectrometer. The MS system can be c o n t r o l l e d by the computer system, which i n c l u d e s a dual 2.5M byte d i s c d r i v e , a Hewlett-Packard Cathode Ray Tube t e r m i n a l , a T e k t r o n i x storage scope ( f o r d i s p l a y ) d r i v e n by a dual 12 b i t d i g i t a l - t o - a n a l o g (D/A) converter, and Versatec p r i n t e r / p i o t t e r . Data was acquired u s i n g a 14 b i t analog-tod i g i t a l (A/D) converter (13 plus s i g n ) . T h i s system can operate and process data a t r a t e s up t o 8 KHz. A thermocouple, i n t e r f a c e d with the Hewlett-Packard 2116C computer, was employed t o sense the temperature during the course o f the thermogravimetric a n a l y s i s . T h i s probe was attached to the TG i n order t o monitor the a c t u a l temperature o f the sample during each r u n . During sample a n a l y s i s , the TG-jet separator connection was wrapped with heating tape and maintained at a temperature o f 125°C while the j e t separator oven was maintained a t 135°C. The MS-jet separator t r a n s f e r l i n e was a l s o wrapped with heat tape and maintained a t 165°C while t h e source temperature was h e l d a t 230°C. The assembly and c a l i b r a t i o n procedures are d e s c r i b e d i n d e t a i l i n reference 23. Depending on the h e a t i n g r a t e , up t o s e v e r a l hundred complete s p e c t r a are obtained as a f u n c t i o n

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

CARRAHER

Thermal Analysis

41

o f temperature with the data a v a i l a b l e as a f u n c t i o n o f absolute i o n abundance and normalized i o n abundance f o r each i o n such that p l o t s o f i o n i n t e n s i t y as a f u n c t i o n o f temperature can be made f o r a l l mass numbers. A number o f m e t a l - c o n t a i n i n g polymers were evaluated employ­ i n g the TG-MS assembly. Organometallic polymers were chosen f o r s e v e r a l reasons. F i r s t , s i n c e degradation o f these compounds t y p i c a l l y occur by d i f f e r e n t routes i n a i r and i n i n e r t e n v i r o n ­ ments, the two environments can be c l e a r l y , e a s i l y d i f f e r e n t i a t e d . Second, some o f the organometallic polymers e x h i b i t good high temperature s t a b i l i t y , l o s i n g l e s s than 20% o f t h e i r i n i t i a l weight t o the 800-1200°C range. I d e n t i f i c a t i o n o f the degrada­ t i o n products from the polymer would be u s e f u l i n b e t t e r under­ standing t h e i r good s t a b i l i t y , and i n d e s i g n i n g and s y n t h e s i z i n g s t i l l more s t a b l e polymers. A t h i r d reason f o r using organo­ m e t a l l i c polymers i n a s s e s s i n o f these m a t e r i a l s occur temperature range ( o f t e n over a range i n excess o f 600 C°) with i n t e r s p e r s e d " s t a b i l i t y p l a t e a u s " . Continuous monitoring o f the evolved chemical products, as i s p o s s i b l e with the TGMS d e s c r i b e d , i s u s e f u l i n understanding these t r a n s i t i o n s i n the degradation sequence. F i n a l l y , the organometallic polymers are good candidates f o r study by TG-MS because they are d i f f i c u l t to c h a r a c t e r i z e by other techniques. Conventional C, Η, Ν elemental a n a l y s i s o f t e n y i e l d s poor r e s u l t s , and s i n c e many o f these polymers are only s p a r i n g l y s o l u b l e i n most s o l v e n t s , c h a r a c t e r i z a t i o n by NMR o r ESR i s not p r a c t i c a l . Methods such as those described h e r e i n are t h e r e f o r e needed f o r c h a r a c t e r i z i n g the s t r u c t u r e s o f such o r g a n o m e t a l l i c polymer m a t e r i a l s . A number o f t i t a n i u m p o l y e t h e r s d e r i v e d from hydroquinone d e r i v a t i v e s were evaluated employing the TG-MS assembly and i n f r a r e d spectroscopy (24). Two general trends were found. F i r s t , the i n i t i a l l y evolved degradation product was c y c l o p e n t a diene t y p i c a l l y appearing about 100°C. Second, t h i s was f o l l o w e d by e v o l u t i o n o f the hydroquinone moiety along with the a s s o c i a t e d oxygens. There was great v a r i a t i o n with respect t o the extent and r a t e o f degradation o f the hydroquinone-containing moiety from the s e v e r a l polymers s t u d i e d , and the q u a n t i t i e s o f organic components i n the f i n a l r e s i d u e s from degradation a l s o v a r i e d markedly.

24

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

42

EFFECTS OF HOSTILE ENVIRONMENTS

The afore suggests that the l i m i t i n g thermally s t a b l e moiety i s the cyelopentadiene m o i e t i e s and that c o n s t r u c t i o n of thermally s t a b l e t i t a n i u m - c o n t a i n i n g polymers should avoid the CppTi moiety. kz a heating r a t e o f 20 CVmin, the c y c l e time f o r sample i s i n excess o f one hour making such determinations commercially costly. More r e c e n t l y we have developed a s i m i l a r assembly except employing a programmable PY i n place o f the TG (JJO. Thus TG are obtained on samples to determine appropriate temperatures f o r MS to be o b t a i n e d . B r i e f l y , uranyl p o l y e s t e r s show three somewhat d i s t i n c t s t a b i l i t y p l a t e a u s . The PY was programmed to heat the samples to the i n c e p t i o n o f the s t a b i l i t y plateaus plus 50 to 100C°. The MS obtained at 250 to 300°C i n d i c a t e d e v o l u t i o n o f water accounting f o r a 5 to 10$ weight l o s s . At 450°C mass fragment mass fragments derived

H H I I -4C—c-4 H

I 25

H

H

The c y c l e can be accomplished w i t h i n 15 mins. making i t commercially more a c c e p t a b l e . Summary Few d e f i n i t i v e thermal s t u d i e s o f metal-containing polymers (with the exception o f s i l i c o n - c o n t a i n i n g polymers) e x i s t i n the l i t e r a t u r e . Thermal a n a l y s i s i s t y p i c a l l y done as a matter o f p r e l i m i n a r y t e s t i n g on new polymers. F u r t h e r , most o f the s t u d i e s were done p r i o r to the advent o f the automatic, programmed thermal a n a l y s i s instruments.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

CARRAHER

Thermal Analysis

43

The lack o f d e f i n i t i v e s t u d i e s i s due to a mixture o f reasons i n c l u d i n g 1) wide v a r i e t y of polymers; 2) newness o f i n t e r e s t i n the area; 3) wide v a r i e t y o f a p p l i c a t i o n s (both p o t e n t i a l and a c t u a l ) o f i n o r g a n i c and organometallic polymers not r e q u i r i n g thermal s t a b i l i t y or thermal a n a l y s i s (uses as anchored metal c a t a l y s i s , c o n t r o l r e l e a s e agents, e l e c t r i c a l and photochemical a p p l i c a t i o n s , s p e c i a l i t y adhesives); 4) i n s u f ­ f i c i e n t d e s c r i p t i o n , i d e n t i f i c a t i o n , o f the products; 5) wider v a r i e t y o f degradation routes and other thermal behavior i n comparison to organic polymers; and 6) many products were synthe­ s i z e d and b r i e f l y c h a r a c t e r i z e d before the advent o f modern thermal i n s t r u m e n t a t i o n . The thermal techniques that have already been u t i l i z e d on more c l a s s i c a l polymers are g e n e r a l l y d i r e c t l y a p p l i c a b l e to organometallic and i n o r g a n i c polymers. The thermal a n a l y s i s of i n o r g a n i c and organometalli d i f f i c u l t i n compariso On the negative s i d e there are 1) a much wider v a r i e t y o f products with many polymers showing a great dependence o f the thermal p r o p e r t i e s on the presence and nature o f i m p u r i t i e s ; 2) general l a c k o f d e f i n i t i v e thermal s t u d i e s and experience upon which to b u i l d ; and 3) added d i f f i c u l t y a s s o c i a t e d with d e f i n i n g thermal responses. On the p o s i t i v e s i d e the wider v a r i e t y o f bond energies present i n organometallic and i n o r g a n i c polymers can allow ( f o r c e r t a i n products) a c l e a r e r i s o l a t i o n and d e f i n i ­ t i o n o f p a r t i c u l a r thermal t r a n s i t i o n s , such as Τ »s and degrada­ t i o n pathways. F u r t h e r , the wider v a r i e t y o f thermal response permits i n c r e a s e d p o t e n t i a l u s e f u l n e s s o f such compounds showing unusual ( e i t h e r i n extent, range, or a c t u a l thermal response) thermal responses. Recommendations There i s a need both f o r s t u d i e s i n v o l v i n g a wide v a r i e t y of products and in-depth s t u d i e s o f s e v e r a l o f these systems. The "survey" s t u d i e s can i n d i c a t e p o t e n t i a l l y i n t e r e s t i n g p o l y ­ mers such as products showing unusual and/or p o t e n t i a l l y u s e f u l thermal responses. The c o r r e l a t i o n o f bonding group, metal atom, and f i n e and gross polymer s t r u c t u r e with such f a c t o r s as degradation pathway, bonding energies and inherent s t a b i l i t i e s should begin. There i s a need to evaluate, by newer thermal a n a l y s i s instrumentation and techniques, polymers p r e v i o u s l y only b r i e f l y c h a r a c t e r i z e d , emphasizing those products which show p o t e n t i a l i n d u s t r i a l a p p l i c a t i o n or other m e r i t o r i o u s p r o p e r t y . Such products should be w e l l c h a r a c t e r i z e d with regard to such f a c t o r s as c h a i n l e n g t h , molecular weight d i s t r i b u t i o n , endgroup, p u r i t y , nature and amount o f i m p u r i t i e s , and a c t u a l morphological s t r u c ­ ture o f the polymer.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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EFFECTS OF HOSTILE ENVIRONMENTS

The i n c r e a s e d a p p l i c a t i o n o f modern thermal techniques and companion techniques must occur i f the thermal c h a r a c t e r i z a t i o n o f o r g a n o m e t a l l i c and i n o r g a n i c polymers i s t o progress. A number o f companion techniques have been shown t o be u s e f u l and merit f u r t h e r use. These i n c l u d e NMR, IR, MS, GC-MS, AA, X-ray microscopy, and GPC. ESR has not been a p p r e c i a b l y u t i l i z e d as a companion technique but may be considered, p a r t i c u l a r l y with polymers c o n t a i n i n g E S R - s e n s i t i v e metals. G e l permeation chromatography (GPC) should be considered as a companion t o o l f o r thermal degradation e v a l u a t i o n s where depolymerization i s suspected. There i s a need f o r a number o f well-chosen thermal a n a l y s i s s t u d i e s o f both the v o l a t i l e products by TGMS, e t c . ( f o r both chemical and t o x i c o l o g i c a l purposes) and the r e s i d u e . Such s t u d i e s should occur throughout the s t u d i e d temperature range r a t h e r than j u s t a t the room and f i n a l temperatures . Acknowledgment The author thanks M a r t e l Z e l d i n f o r h i s help i n p r e p a r i n g the s e c t i o n on d i f f e r e n t i a t i o n o f depolymerization mechanisms.

Literature Cited

1.

C. Carraher, J. Macromol. Sci.-Chemistry, A17(8), 1293 (1982). 2. E. Horowitz, M. Tryon, R. Christensen and T.P. Perros, J. Appl. Polym. Sci., 9, 2321 (1915). 3. G. Gee, Chem. Soc. (London) Spec. Publ. No. 15, 65 (1961). 4. C.S. Marvel and M.M. Martin, J. Amer. Chem.Soc.,619 (1958). 5. C. Carraher and J. Schroeder, Polymer P.,19(2),619 (1978). 6. C. Carraher, V. Foster, H. Molloy, M. Taylor, T, Tiernan and J. Schroeder, J. Macromol. Sci.-Chem., A16(1), 231 (1981). 7. R. Brotherton, Conference on High Temperature Polymer & Fluid Research, A50-TDR-62-372 (August 1962), p. 389. 8. K. Andrianov, Soc. Chem. Ind. (London) Monograph No. 13, 75 (1961). 9. K. Andrianov, Metalorganic Polymers, Interscience, NY, 1965. 10. E. Neuse, H. Rosenberg and R. Carlen, Macromolecules, 1, 424 (1968). 11. A.W. Laubengayer, P.C. Moews and R.F. Porter, J. Amer. Chem.Soc.,83, 1337 (1961). 12. C.W. Lewis, J. Polymer Sci., 33, 153 (1958). 13· A.V. Tobolsky, Inorganic Polymers, Academic Press, N.Y., 1962, pp. 10-27.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

4.

14. 15.

16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

CARRAHER

Thermal Analysis

C. Carraher and J . Schroeder, Unpublished r e s u l t s . E. P e t e r s , D. Stewart, J . Bohan, R. M o f f i t t , C. Beard, G. Kwiatkowski and E. Hedayn, J . Polymer S c i . , 15, 973 (1977). M.B. R o l l e r and J.K. G i l l h a m , Polym. Eng. S c i . , 14, 567 (1974). E.M. Barrall, M. Flander and J.A. Logan, Thermochim. Actn, 5, 415 (1973). P.J. James, E.M. B a r r a l l , B. Dawson and J.A. Logan, J . Macromol. Sci.-Chem., A8, 135 (1974). R.W. F i n c h , Analabs Res. Notes, 1 0 ( 3 ) , 1 (1970). J.F. Brown, L. Vogt, A. Karchman, J . Eustance, K. K i s e r and K. Krantz, J . Amer. Chem. Soc., 82, 6194 (1960). J.F. Brown, J . Polymer S c i . , C1, 83 (1963). P. N a n n e l l i , H. G i l l m a r Sci., A-1, 9, 3027 (1971) C. Carraher, H. Molloy, T. T i e r n a n , M. T a y l o r and J . Schroeder, J . Macromol. Sci.-Chem., A16(1), 195 (1981). C. Carraher, H. Molloy, T. T i e r n a n , S. T s u j i , M. T a y l o r and S. C o l d i r o n , Unpublished r e s u l t s . J.R. MacCallum, European Polymer J . , 2, 413 (1966).

RECEIVED January 20, 1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

5 New Styrene-Maleic Anhydride Terpolymer Blends W. J. HALL, R. L. KRUSE, R. A. MENDELSON, and Q. A. TREMENTOZZI Monsanto Company, Indian Orchard, MA 01151

A group of new consisting of variou terpolymers blended with styrene-acrylonitrile copolymer and rubber-modified versions of these materials have been prepared and investigated. In particular the effects of chemical composition of the components on heat resistance and the miscibility behavior of the blends have been elucidated. Toughness and response to elevated temperature air aging are also examined. Appropriate combinations of the components may be melt blended to provide an enhanced balance of heat resistance, chemical resistance, and toughness. Engineering p l a s t i c s are g e n e r a l l y developed to provide appropriate property response to i n c r e a s i n g l y severe environmental c o n d i t i o n s ; e.g., heat, s t r e s s a t temperature extremes, and chemicals. A number o f such polymers have been introduced i n recent y e a r s , each with i t s own balance o f p r o p e r t y advantages and disadvantages. Simultaneously, research on polymer c o m p a t i b i l i t y has s i g n i f i c a n t l y increased the number o f known completely m i s c i b l e polymer p a i r s (I), which g e n e r a l l y show approximate a d d i t i v i t y o f many p r o p e r t i e s as a f u n c t i o n o f component r a t i o . This c h a r a c t e r i s t i c can, i n p r i n c i p l e , be used to create a f a m i l y o f m a t e r i a l s with optimized property combinations, among which are those p r o p e r t i e s which q u a l i f y such polymer blends as engineering p l a s t i c s . This paper d i s c u s s e s a group o f new f u l l y m i s c i b l e polymer p a i r s c o n s i s t i n g o f v a r i o u s styrene-maleic anhydride random terpolymers (S/MA/X) and s t y r e n e - a c r y l o n i t r i l e random copolymer (SAN) and rubber modified v e r s i o n s of these p a i r s . Appropriate combinations can provide an enhanced balance o f heat r e s i s t a n c e , chemical r e s i s t a n c e , and toughness. The termonomers i n S/MA/X to be d i s c u s s e d are a c r y l o n i t r i l e (S/MA/AN), e t h y l a c r y l a t e (S/MA/ETA), i s o b u t y l e n e (S/MA/IB), methyl a c r y l a t e (S/MA/MEA), and methyl methacrylate

0097-6156/ 83/0229-0049506.00/0 © 1983 American Chemical Society In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

50

(S/MA/MM). M i s c i b i l i t y behavior of t y p i c a l matrix p a i r s i s discussed as a f u n c t i o n of composition, and d i s c u s s i o n of m a t e r i a l behavior i n t h i s work emphasizes response to elevated temperatures and to s t r e s s at temperature extremes. Thus, g l a s s t r a n s i t i o n temperature (Tg), d i s t o r t i o n temperature under load (DTUL), and t e n s i l e deformation p r o p e r t i e s as a f u n c t i o n of temperature are reported f o r v a r i o u s t y p i c a l blend combinations. A l s o discussed are the r e s u l t s of elevated temperature a i r aging s t u d i e s on a t y p i c a l blend compared to ABS. Experimental The v a r i o u s copolymer and terpolymer samples, with or without g r a f t e d polybutadiene rubber, were produced by conventional f r e e r a d i c a l p o l y m e r i z a t i o n s . Blending was performed using one of mixing bowl, Brabender i n t e n s i v e mixer or l a r g e s c a l e extruder, depending on the s c a l e of the experiment d e s i r e d . In the work discussed here no e f f e c t of b l e n d i n g s c a l e was observed. Tg's reported here were measured by d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC), using a DuPont 990 Thermal A n a l y z e r , at 20°C/min. h e a t i n g rate and t a k i n g the onset value as Tg. DTUL measurements were performed according to ANSI/ASTM D648 with 1.82 MPa maximum f i b e r s t r e s s l o a d i n g on unannealed specimens with dimensions given a p p r o p r i a t e l y i n the R e s u l t s and D i s c u s s i o n s e c t i o n . T e n s i l e deformation measurements were performed at v a r i o u s temperatures according to ANSI/ASTM D638 on i n j e c t i o n molded Type I (12.7 χ 3.2 χ 57 mm gauge dimensions) specimens, using an I n s t r o n U n i v e r s a l T e s t e r and Instron constant temperature chamber (the l a t t e r f o r a l l temperatures other than room temperature (R.T. = 23°C)). T e n s i l e t e s t i n g speed was 5.08 mm/min. (0.2 in./min.) g r i p s e p a r a t i o n rate i n a l l cases. Izod impact t e s t i n g was performed according to ASTM D256 on 12.7 χ 3.2 χ 63 mm specimens, i n j e c t i o n molded i n the case of the aging study and compression molded i n the cases given i n Table I. Specimens were notched to a depth of 2.5 mm with a root radius of 0.25 mm. The elevated temperature aging study was performed on i n j e c t i o n molded t e n s i l e , Izod, and DTUL specimens (dimensions given above) which were maintained i n a c i r c u l a t i n g a i r oven at an a c c u r a t e l y c o n t r o l l e d 90°C f o r p e r i o d s of time up to two months. When removed from the a i r oven, these specimens were conditioned at 23°C and 50% R.H. f o r at l e a s t 24 hours before t e s t i n g . Notching of the Izod bars was performed on conditioned specimens. R e s u l t s and D i s c u s s i o n Of major importance i n the development of most engineering p l a s t i c s i s the r e t e n t i o n of r i g i d i t y to as high a use

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

5.

H A L L ET AL.

Styrene-Maleic Anhydride Terpolymer Blends

51

temperature as i s p o s s i b l e c o n s i s t e n t with the o p t i m i z a t i o n o f such other p r o p e r t i e s as toughness, r e s i s t a n c e t o chemical a t t a c k , appearance o f the f a b r i c a t e d a r t i c l e , e t c . Thus, temperature, o r heat, may be considered t o be a h o s t i l e environment t o which the engineering p l a s t i c i s submitted. A wide v a r i e t y o f S/MA/X terpolymers were i n v e s t i g a t e d t o create the optimum balance o f p r o p e r t i e s t a k i n g advantage o f the well-known enhancement o f Tg with i n c r e a s e o f MA i n S/MA. In t h i s paper we d i s c u s s the e f f e c t o f terpolymer composition on r i g i d i t y i n terms o f Tg and, i n p a r t i c u l a r , DTUL. F i g u r e 1 shows a p l o t o f DTUL ( i n t h i s case, 12.7 χ 12.7 χ 127 mm i n j e c t i o n molded specimens) vs. MA content f o r S/MA copolymers (from the data o f the l a t e Dr. Y. C. Lee (2)) and, as an example o f the terpolymer cases, o f Tg vs. MA content i n S/MA/MM terpolymer a t ca. 6% (wt.) methyl methacrylate. The rate o f i n c r e a s e o f Tg with MA content i s approximatel shows DTUL (12.7 χ 3.2 percent o f the t h i r d monomer f o r the cases o f S/MA/AN, S/MA/IB, and S/MA/MM, both g l a s s y polymer and rubber modified v e r s i o n s , where the data are taken from Lee (2) and Lee and Trementozzi (3, 4). The methyl a c r y l a t e and e t h y l a c r y l a t e cases are not shown i n order t o preserve c l a r i t y i n the f i g u r e , but both give somewhat lower DTUL s a t comparable (wt.) compositions. In a l l rubber-modified (R.M.) cases the percent o f a component given i s based on t o t a l m a t e r i a l , and i n the R.M.S/MA/AN case DTUL data f o r samples v a r y i n g from ca. 17 t o 23% MA are normalized t o a constant 20% MA content. S u r p r i s i n g l y , i n the methyl methacrylate case a broad maximum i n DTUL i s observed. This i s c o n s i s t e n t with Tg data, not shown here, f o r these m a t e r i a l s . Terpolymer composition a l s o a f f e c t s toughness. The p a r t i c u l a r case o f S/MA/AN i s i l l u s t r a t e d i n Table I , where three samples o f v a r y i n g AN content, but roughly comparable MA and rubber contents are d e s c r i b e d i n terms o f Izod impact. In t h i s case i t may be seen that i n c r e a s i n g AN l e v e l i n the terpolymer leads t o a general i n c r e a s e i n the Izod impact s t r e n g t h . The apparent equivalence o f the 0% and 5% AN cases may suggest that 5% AN i n the terpolymer i s too low a l e v e l to cause a s e n s i b l e e f f e c t on impact s t r e n g t h . A l s o shown are two blends o f the 5.1% AN S/MA/AN terpolymer with ABS (one blend c o n t a i n i n g Of-methyl styrene/AN copolymer f o r Tg improvement). Significant toughening i s observed i n these l a t t e r cases. Blending o f polymer with ABS o f f e r s c e r t a i n s i g n i f i c a n t property enhancement o p p o r t u n i t i e s such as r e s i s t a n c e t o chemical a t t a c k which increases with i n c r e a s i n g AN content, toughening, and m o d i f i c a t i o n o f p r o c e s s a b i l i t y c h a r a c t e r i s t i c s . However, such o p p o r t u n i t i e s can only be r e a l i z e d i f s u f f i c i e n t m i s c i b i l i t y of the g l a s s y (matrix) components i s achieved t o r e t a i n or enhance toughness; and p r e d i c t a b l e v a r i a t i o n o f p r o p e r t i e s with blend r a t i o i s t o be expected only f o r l a r g e l y or f u l l y m i s c i b l e matrix components. F o r t h i s reason, a study o f the m i s c i b i l i t y 1

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

52

EFFECTS OF HOSTILE ENVIRONMENTS

Table I.

Izod Impact Strength of S/MA/AN Terpolymers

Material

*% AN

R.M. S/MA R.M. S/MA/AN R.M. S/MA/AN —R.M. S/MA/AN//ABS//of-MS/AN (50/38/12 by wt.) —R.M. S/MA/AN//ABS (60/40 by wt.)

%

MA

and

% Rubber

Blends Izod Impact (J/m)

0 5.1 9.5 2.5

20.7 22.3 19.9 11.1

13.7 14.3 13.4 20.0

112 112 135 157

3.1

13.4

21.9

157

"Percentage based on t o t a l blend composition except % AN includes only terpolyme — B l e n d s with ABS mad

given

% MA IN S/MA/MM TERPOLYMER

% MA IN S/MA COPOLYMER Figure 1. Effect of maleic anhydride content on distortion temperature under load (DTUL) and on glass transition temperature (Tg). Key: o, S/MA copolymer; and Δ, S/MA/MM terpolymer (ca. 6% MM).

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

HALL ET AL.

Styrene-Maleic Anhydride Terpolymer Blends

-.180

Φ

1301

8

12

16

20

WT. PERCENT TERM0N0MER Figure 2. Effect of termonomer content on DTUL in glassy and rubber-modified terpolymers. Key.o, S/MA/AN(25%)MA);e, R.M. S/MA /AN(correctedto 20% MA; ca. 14ψ rubber); •, RM. S/MA/IB(29ψ MA; 18ψ rubber); Δ, S/MA/MM; ν, R.M. S/MA/MM (22.5% MA; ca. 14ψ rubber). 0

0

0

0

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

54

EFFECTS OF HOSTILE ENVIRONMENTS

of the terpolymers with SAN over a range o f compositions o f the components was undertaken. The p a r t i c u l a r case o f S/MA/MM and SAN i s d i s c u s s e d here as an example. Tg behavior and o p t i c a l c l a r i t y were used t o c h a r a c t e r i z e m i s c i b i l i t y . Thus the o b s e r v a t i o n o f a s i n g l e Tg i n a blend, combined with o p t i c a l c l a r i t y , i s taken t o i n d i c a t e t o t a l m i s c i b i l i t y , while two Tg's i d e n t i c a l with those o f the pure components i n d i c a t e i m m i s c i b i l i t y , and two Tg's a t temperatures between those o f the pure components i n d i c a t e p a r t i a l m i s c i b i l i t y (5). F i g u r e 3 i l l u s t r a t e s two immiscible blend composition cases, (a) and ( e ) , and three m i s c i b l e blend composition cases, ( b ) , (c) and ( d ) , where the compositions o f the components are given i n the f i g u r e ; and i n a l l but one case f i v e blend r a t i o s were i n v e s t i g a t e d . (The data i n F i g . 3(a) are f o r SAN//S/MA copolymer.) I t was noted f o r a l l systems s t u d i e d that a t any p a r t i c u l a r p a i r o f component compositions th i . e . , m i s c i b l e , immiscible with changing component p a i r r a t i o . Moreover, temperature dependent o p t i c a l t r a n s m i s s i o n experiments on a programmed hot stage gave no evidence o f a phase change, i . e . , lower c r i t i c a l s o l u t i o n temperature behavior, t o temperatures w e l l i n t o the p r o c e s s i n g range f o r any o f the ( g l a s s y s t a t e ) m i s c i b l e blends. Moreover, the presence of methyl methacrylate, a t l e a s t t o 13%, i n the terpolymer does not appear to a f f e c t m i s c i b i l i t y (see F i g u r e 3 ) . These observations allow a simple two-dimensional mapping o f the m i s c i b i l i t y composition r e g i o n i n terms o f percent AN i n the SAN vs. percent MA i n the S/MA/MM, as shown i n F i g u r e 4, where both S/MA copolymer and terpolymers o f v a r y i n g MM l e v e l s are represented. As may be seen i n F i g u r e 4, a r e l a t i v e l y wide r e g i o n o f m i s c i b l e component compositions i s a v a i l a b l e , p e r m i t t i n g a l l o y i n g o f the terpolymer with ABS. This r e s u l t i s q u a l i t a t i v e l y c o n s i s t e n t with the roughly s i m i l a r dependence o f s o l u b i l i t y parameter on copolymer composition i n the SAN and S/MA cases, as may be c a l c u l a t e d from molar a d d i t i v i t y r u l e s (see (6)). A l s o , the s o l u b i l i t y o f SAN with i t s e l f and with p o l y s t y r e n e has been reported by Molau (7) and i s c o n s i s t e n t with F i g u r e 4. S i m i l a r m i s c i b i l i t y behavior with SAN was observed i n the cases o f the other terpolymers. Blending o f the high heat r e s i s t a n t terpolymer with ABS t o form a m i s c i b l e matrix phase, as d e f i n e d i n F i g u r e 4, i s o f course, expected t o i n c r e a s e the heat r e s i s t a n c e o f the ABS. The data i n Table I I , taken from references (2-4), provide a systematic r e p r e s e n t a t i o n o f the v a r i a t i o n o f DTUL with terpolymer/ABS blend composition f o r the AN, IB, and MM-containing terpolymers (both g l a s s y and rubber-modified). In some o f these cases, as noted, a copolymer o f Of-methyl s t y r e n e / a c r y l o n i t r i l e was added to the f o r m u l a t i o n . From these data i t i s apparent t h a t DTUL does, indeed, i n c r e a s e with i n c r e a s i n g terpolymer c o n c e n t r a t i o n i n the blends. Moreover, the e f f e c t o f the terpolymer composition on DTUL o f the blends i s

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

50

100 0 θ A

100 0 θ A 50

100 0 θ A

50

WEIGHT PERCENT COMPONENT Β IN BLEND

50

100 0 Β A

50

190 100 θ

Figure 3. Glass transition temperature-composition plots for various SA N// S/ MA / MM blends to illustrate miscibility behavior.

9Q

EFFECTS OF HOSTILE ENVIRONMENTS

70

Γ

60h


260

2

>260

3 4

218 49

d

a. 20.7 MPa = 3000 psi; 69 MPa m 10,000 psi b. Glass/mineral filled c. 40% Glass fiber

d. 30% Glass fiber e. Glass/mineral filled PET f. 30% Glass fiber

Property Maintenance At Elevated Temperature A second aspect of thermal resistance involves retention of properties at elevated temperatures. Determination of properties of 40% glass-reinforced molding grade of PPS over temperatures ranging from room temperature to 205°C (400°F) shows classical deterioration above the glass transition temperature. Fortunately, because of crystallinity effects and good compatability with the glass reinforcement the loss in strength is gradual and even at temperatures of 205°C considerable strength integrity is retained. In general, with exception to impact strength which increases as temperature increases, 40% glass-reinforced moldings retain about 80% of their original strength at 100°C (212°F), 60% at 160°C (320°F) and 40% at205°C(9). Weatherability Outside exposure to the elements can certainly take its toll on plastic materials, particularly those not properly protected by stabilizers. Unstabilized tensile bars of 40% glass-filled PPS were aged in an Atlas Weatherometer for 10,000 hours. Moderate stability was observed as shown in Table IX. The loss in tensile strength was reduced from 37% to 9% by adding 1 % Tinuvin 327 stabilizer.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

6. VIVES ET AL.

81

Polyphenylene Sulfide

Table IX. Weather-ometer Tests On 40% Glass-reinforced PPS Hours Exposed

Tensile Strength, MPa No „Stabilizer 1%Tinuvin- 327 )

0 2,000 6,000 8,000 10,000

i

|

j

z

e

r

115 105 106 98.9 72.7

113 109 104 97.8 103

Flammability Although PPS, like most organic materials, will burn when exposed to an external flame, its aromatic chemical structure and its innate ability to char when expose flame resistance. In its unfilled form it exhibits a high oxygen index of 44. Addition of a glass and mineral filler raises the index to ca. 55. PPS provides a low radiant panel flame spread index (ASTM EP162) and according to standard UL (UL94) laboratory flammability tests is classifiecl as V-0/5V (i.e., self extinguishing, non-dripping). Unlike other aromatic polymers such as polystyrene and inherently flame resistant structures such as polyvinyl chloride, PPS does not produce large amounts of smoke in either the smoldering or flaming states (NBS Test Chamber). PPS has an auto-ignition temperature of 540°C (1004°F). Comparative oxygen indexes and smoke density data are provided in Tables X and XI (10,11). Table X. Oxygen Index Values For Plastics Plastic Polyolefin SAN ABS Nylon Polycarbonate PPO Polysulfone Polyimide PPS PVC PTFE

Oxygen Index 18 19 19 24 24 25 30 37 44-55 45 95

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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EFFECTS OF HOSTILE ENVIRONMENTS

Table XI. Smoke Density. National Bureau Of Standards Test Maximum Specific Optical Density, Dm Material, (thickness) A Red Oak (6.4 mm) 353 75 Polystyrene (6.4 mm) (6.4 mm)a 395 780 Polyvinyl Chloride (3.2 mm) 270 525 Nylon 6/6 (3.2 mm)b 487 41 Polysulfone (6.4 mm)c 111 370 Polycarbonate (3.2 mm) 21 324 Phenolic (3.2 mm)d 110 50 Polyphenylene Sulfide (6.4mm)e 25 232

Obscur. Time (D = 16)*, min. A Β s

47I

SO

4.0 24.0 3.6 12.6 27.0 5.0

0.63 0.50 9.20 1.90 2.00 5.80

15.5

3.20

A = Smolderin a. UCCSMD-3500 b. 40% glass filled c. P-1700

e. Ryton PPS R-4, 40% glass filled f. Time required for specific optical density(Ds) to reach value of 16.

Radiation Resistance Relatively high exposures of gamma radiation have no significant effect on the mechanical properties of glass-reinforced and glass- and mineral-containing PPS compounds. (Table XII) As shown in Table XIII, neutron radiation nas only a slight effect on these compounds. Table XII. Effect Of Gamma Radiation On Mechanical Properties Of PPS Compounds^

a. b. c. d.

Retained Strength Compared to No Exposure, % Compound Flex Str Ten Str Flex Mod 40% Glassreinforced^ 93 100 102 Glass-reinforced, mineral-filledc 94 101 102 Glass-reinforced, mineral-filledd 99 98 102 Radiation dose of 3x108 rad Initial values: FS, 184 MPa; TS, 148 MPa; FM, 1.27x10* MPa Ryton R-8. initial values: FS, 111 MPa; TS.83MPa; FM, 1.22x10* MPa. Ryton R-10 7006A, initial values: FS, 144 MPa; TS, 95 MPa; FM 1.49x10* MPa

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

6. VIVES ET AL.

83

Polyphenylene Sulfide

Table XIII. Effect Of Neutron Radiation On Mechanical Properties Of PPS Compoundsa Retained Strength Compared to No Exposure, % Compound Hex Str Ten Str Flex Mod 40% Glassreinforcedb

86

90

102

Glass-reinforced, mineral-filled*

88

90

100

Glass-reinforced, mineral-filledd

95

87

96

a b c d

Total thermal neutro Initial values as given in Table XII. Ryton R-8, initial values as given in Table XII. Ryton R-10 7006A, initial values as given in Table XII.

Applications The outstanding thermal stability and chemical resistance of PPS compounds have led to their use in applications ranging from food warmers to nuclear installations. Some of the harsh environments which these compounds are successfully withstanding are shown in the following applications: Integrated circuit device burn-in test sockets. These chip carriers must survive high continuous test oven temperatures. Oxygen sensor connector insulators. These parts must withstand the high temperatures of automotive engines. Oil well sucker rod guides. These components must not only tolerate the extreme temperatures of deep oil wells, but must remain unaffected by the hot oil and corrosive liquids. Chemical pumps. Pump housings and impellers of PPS compounds withstand corrosive liquids that would destroy metal components. Carburetors. A PPS compound has replaced aluminum in a carburetor for a small gas engine. ρ H meters. In one case, pH meters with PPS components have served over three years without failure in a corrosive chemical application where stainless steel meters typically failed in two months. Flue stack filter bags. Fabric made of PPS fiber has shown superior resistance to the hot sulfur dioxide gases of coal-fired boilers, thus providing environmental protection.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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EFFECTS OF HOSTILE ENVIRONMENTS

Electrical connectors. In some applications, electrical components of PPS compounds undergo assembly operations in which they are exposed for brief times to solder baths well above 300°C. Thermostat housing. These components must survive the heat and chemical attack of automotive coolants for prolonged service periods. Diesel engine piston cooling nozzles. Before acceptance, these components had to withstand several thousand hours of continuous exposure to the hot lubricating oil of heavy duty diesel engines. Lighting reflectors. In this application, a high temperature plastic that meets reflectance design requirements and that has long term resistance to ca 240°C is required. Examples include floodlamps and halogen lamps. Capacitor components. In some capacitor applications, long term resistance to polar organic solvents is required. Automotive. PPS is often the choice due to thermal stability and chemical resistance. Its compounds are used in emission control, fuel, ignition, cooling, brake an Industrial valves. A unique ball valve made from a PPS composition has gained wide recognition in the paper-making industry for its effectiveness in the containment of corrosive liquids. Coatings. The thermal and chemical resistance of polyphenylene sulfide has led to a wide variety of applications as a coating material. Examples are cookware with heat-resistant, easy-release coatings containing PPS, valves and fittings coated with PPS for protection against corrosive chemicals, and electrical coils coated with PPS as a temperature-resistant insulation. Electrical Bobbins. PPS compounds are used in these components of solenoids and transformers where resistance to temperatures of up to 180°C is required. Fuel Filters. PPS compounds because of their chemical resistance and temperature stability are suitable for use in this application where service temperatures can range from -40°C to 200°C. Microwave oven applications. A special grade of PPS compound is produced for use in microwave ovenware, where its chemical resistance and thermal stability combined with low absorption of the microwave energy make it attractive for this application. PPS compounds are also used in components of microwave ovens. Literature Cited

1. Edmonds, J. T., Jr.; Hill, H. W. Jr. U.S. Patent 3354129, 1967. 2. Brady, D. G.; Hill,H.W., Jr. Modern Plastics, 1974, 51, 60. 3. Plastics World 1977, 35, 30. 4. Plastics Technology 1982, Oct., 101. 5. Miller, J. R.; Dix,J.S.; Vives, V. C. Proc. Automotive Plastics Durability Conf. SAE 1981, 75-78. 6. Plastics Compounding 1982, July/August, 49. 7. Wake, W.C.in"Fillers for Plastics", Wake, W. C., Ed.; Butterworth: London, 1971, Chap. 1.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

6. VIVES ET AL. Polyphenylene Sulfide

85

8. Moska, J.C.Reg. Tech. Conf. Soc. Plast. Eng. 1980, 127-133. 9. Hill, H. W., Jr.; Brady, D. G. in "Kirk-Othmer Encyclopedia of Chemical Technology"; John Wiley: New York, 1982, Vol. XVIII, p. 793. 10. Hilado, C. S. "Oxygen Index of Materials", Fire and Flammability Series, Technomic: Westport, CT. 1973, Vol. IV. 11. Hilado, C. S. "Flammability Handbook for Plastics", Technomic: Westport, CT., 1974, p. 60. RECEIVED

February 22, 1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7 Advances in High-Performance Polymers RAYMOND B. SEYMOUR University of Southern Mississippi, Department of Polymer Science, Hattiesburg, MS 39406-0076

While polymers with moderately high performance qualities, such been known for years be extruded or injection molded. However, they were able to withstand the effects of moderately hostile environments. The classic reinforced thermosets could be compression molded and could also be classified as high performance plastics. In contrast, the general purpose thermoplastics, introduced in the 1930's, were readily extruded and injection molded but were not useful at boiling water temperatures. Fortunately, the deficiencies of both the classic thermosets and general purpose thermoplastics have been overcome by the commercialization of a series of engineering plastics including polyacetals, polyamides, polycarbonate, polyphenylene oxide, polyaryl esters, polyaryl sulfones, polyphenylene sulfide, polyether ether ketones and polyimides. Many improvements in performance and processing of these new polymers may be anticipated through copolymerization, blending and the use of reinforcements. Polymers w i t h moderately high performance q u a l i t i e s , such as c e l l u l o s e and cotton and wood have been known f o r c e n t u r i e s . These l i n e a r polymers could not be extruded or i n j e c t i o n molded but they d i d withstand the e f f e c t s of moderately high h o s t i l e environments. The c l a s s i c thermosets, such as e b o n i t e , p h e n o l i c s , ureas, melamines and p o l y e s t e r s as w e l l as the epoxies, when r e i n f o r c e d w i t h f i b e r g l a s s or g r a p h i t e f i b e r s could a l s o be c l a s s i f i e d as high performance thermosets. While these p l a s t i c s cannot be r e a d i l y extruded or i n j e c t i o n molded, they are r e s i s t a n t to the e f f e c t s of moderately high h o s t i l e environments. P h e n o l i c r e s i n mortars have been used f o r over a h a l f century f o r the c o n s t r u c t i o n of chemical r e s i s t a n t v e s s e l s and f o r j o i n i n g b r i c k and t i l e used as l i n i n g s i n hot a c i d environments. (jk) 0097-6156/83/0229-0087$06.00/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

88

The general purpose t h e r m o p l a s t i c s introduced i n the 1930 s and 1940 s were r e a d i l y f a b r i c a t e d by e x t r u s i o n and i n j e c t i o n molding techniques. T h e r m o p l a s t i c s , such as p o l y v i n y l c h l o r i d e , polystyrene and polyethylene were r e s i s t a n t to m i n e r a l a c i d s at temperatures up to 60°C but they could not be used at higher temperatures, such as that of b o i l i n g water. These l a r g e volume p l a s t i c s had other c h a r a c t e r i s t i c d e f i c i e n c i e s which were o v e r come by the use of a d d i t i v e s . The b r i t t l e n e s s of p o l y v i n y l c h l o r i d e and polystyrene was decreased by b l e n d i n g w i t h p l a s t i c i z e r s or impact modifying polymers. The f l a m m a b i l i t y of polystyrene and p o l y o l e f i n s was decreased by the a d d i t i o n of flame r e t a r d a n t s and the i n s t a b i l i t y of p o l y v i n y l c h l o r i d e and polypropylene was reduced by the a d d i t i o n of s t a b i l i z e r s The s t r e n g t h and heat r e s i s t a n c e of a l l of the general purpose p l a s t i c s were improved by r e i n f o r c i n g w i t h f i b e r g l a s s or g r a p h i t The heat r e s i s t a n c by post c h l o r i n a t i o n , the d u c t i l i t y of polyethylene was improved by i n c r e a s i n g the molecular weight and the u s e f u l n e s s of p o l y styrene was increased by c o p o l y m e r i z a t i o n w i t h a c r y l o n i t r i l e . N e v e r t h e l e s s , i n s p i t e of improvement i n performance, r e s u l t i n g from these m o d i f i c a t i o n s , most general purpose p l a s t i c s were under engineered f o r many a p p l i c a t i o n s . Blends of copolymers of styrene and a c r y l o n i t r i l e and butadiene and a c r y l o n i t r i l e c a l l e d ABS p l a s t i c s which are more d u c t i l e than p o l y s t y r e n e , are now used at an annual r a t e of almost 500 thousand t o n s . Terpolymers of s t y r e n e , a c r y l o n i t r i l e and m a l e i c anhydride (Cadon) have heat d e f l e c t i o n p o i n t s above 100°C.(_3)While the p h y s i c a l p r o p e r t i e s of both ABS and the m a l e i c anhydride terpolymers are s u p e r i o r to p o l y s t y r e n e , the improvements are not s u f f i c i e n t to c l a s s i f y them as high performance plastics. N e v e r t h e l e s s , these medium performance p l a s t i c s can be used i n many a p p l i c a t i o n s which are u n s u i t a b l e f o r general purpose p l a s t i c s . More important, these p l a s t i c s , which are a l s o moderately expensive, may be upgraded by changes i n f o r m u l a t i o n . For example, ABS which, w i t h an annual s a l e of 450 thousand t o n s , i s the l a r g e s t s e l l i n g engineering p l a s t i c s , can be upgraded by r e p l a c i n g the a c r y l o n i t r i l e - b u t a d i e n e copolymer elastomer (NBR) w i t h ethylene-propylene copolymer elastomer (EDPM). The h i s t o r y of e a r l y developments i n high performance polymers has been recorded by s e v e r a l pioneers i n polymer science.(4)These polymers are d i s c u s s e d i n t h i s a r t i c l e under s p e c i f i c headings. 1

1

P o l y a c e t a l s (POM) Polyoxymethylene, which p r e c i p i t a t e s spontaneously from u n i n h i b i t e d aqueous s o l u t i o n s of formaldehyde, was i s o l a t e d by

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7. SEYMOUR

89

High-Performance Polymers

B u t l e r o v i n 1859 and i n v e s t i g a t e d by Nobel l a u r e a t e Staudinger i n the 1 9 2 0 s . Polyoxymethylene s t a b i l i z e d by a e e t y l a t i o n of the hydroxyl end groups (capping) was introduced commercially by DuPont under the trade name of D e l r i n i n the l a t e 1950 s Λ — ' The s t r u c t u r e of the r e p e a t i n g u n i t i n POM i s f

1

fCH -0* 2

Stable a c e t a l copolymers of formaldehyde, c a l l e d Hostoform and Celcon were a l s o produced commercially by the c a t i o n i c c o p o l y m e r i z a t i o n of formaldehyde w i t h ethylene oxide/—' The s t r u c t u r e of the repeating u n i t i n the copolymer i s •rCH2-0-eH -CH -0-r 2

2

These h i g h performanc annual r a t e of 45 thousan annual production i n the l a t e 1980 s w i l l be 80 thousand t o n s . A t y p i c a l g l a s s f i l l e d (25%) a c e t a l polymer w i l l have the f o l l o w ­ ing p r o p e r t i e s : T

t e n s i l e strength (psi) 18,500 e l o n g a t i o n (%) 3 f l e x u r a l strength (psi) 28,000 f l e x u r a l modulus ( p s i ) 1,100,000 i z o d impact ( f t l b s / i n of notch) 1.8 Rockwell hardness M79 m e l t i n g point (°C) 175 d e f l e c t i o n temperature (°C) (§ 264 p s i 150 The s e l l i n g p r i c e of p o l y a c e t a l and other engineering p l a s t i c s i s about o n e - h a l f that of cast m e t a l s . P o l y a c e t a l s have been approved by the Food and Drug A d m i n i s t r a t i o n f o r contact w i t h foods. Some of the uses f o r molded p o l y a c e t a l s are as f o l l o w s : v a l v e s , f a u c e t s , b e a r i n g s , a p p l i a n c e p a r t s , s p r i n g s , automobile window b r a c k e t s , hose clamps, h i n g e s , gears, shower heads, pipe f i t t i n g s , video c a s s e t t e s , tea k e t t l e s , c h a i n s , f l u s h t o i l e t f l o a t arms, pasta machines, desk top s t a p l e r s and a i r gun p a r t s . These unique polymers are r e s i s t a n t to many s o l v e n t s , aqueous s a l t and a l k a l i n e s o l u t i o n s and weak a c i d s at a pH g r e a t e r than 4 . 5 . More complete data on p h y s i c a l p r o p e r t i e s and r e s i s t a n c e to h o s t i l e environments of these and other polymers are a v a i l a b l e ' Polyamides Nylon-66, which was the c l a s s i c h i g h performance thermo­ p l a s t i c was produced by Carothers i n the 1930 s by heating the p u r i f i e d s a l t produced by the r e a c t i o n of a d i p i c a c i d and hexamethylenediamine/—' Over 125 thousand tons of these polyamides 1

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

90

are used annually as h i g h performance p l a s t i c s i n the U.S. It i s a n t i c i p a t e d that t h i s use w i l l exceed 180 thousand tons annually i n the l a t e 1 9 8 0 s . Glass f i l l e d Nylon-66 w i t h a heat d e f l e c t i o n temperature of 250°c(iand a transparent n y l o n - 6 6 ( M k r e a v a i l a b l e commerciall y . Molded nylon-66 i s being used f o r lawn mower b l a d e s , b i c y c l e wheels, t r a c t o r hood e x t e n s i o n s , s k i s f o r snowmobiles, skate wheels, motorcycle crank cases, bearings and e l e c t r i c a l c o n n e c t i o n s . The r a d i a t o r i n the 1982 model Ford Escort i s molded from n y l o n - 6 6 . The s t r u c t u r e of d y d a c t i c nylons, such as nylon-ab i s f

H

HO

I

T

0

I II

II

N-(CH ) -N-C-(CH ) _ -C^ 2

a

2

b

2

where a and b are equal to the number of carbon atoms i n the repeating u n i t s of the diamine and d i c a r b o x y l i c a c i d . Mono and b i a x i a l l y o r i e n t e d nylon f i l m i s a v a i l a b l e . ( I D Nylon-610 and nylon-612 produced by the condensation of hexamethylenediamine and s e b a c i c or dodecanoic a c i d , r e s p e c t i v e l y , are more r e s i s t a n t to moisture and more d u c t i l e than nylon-66. The p r o p e r t i e s of these polyamides may be improved by the formation of polyether b l o c k s (NBC) and by b l e n d i n g w i t h t h e r m o p l a s t i c s , such as EPDM, PET, PBT and TPE. NBC (Nyrim) i s more expensive than RIM polyurethane but i t may be heated to 200°C without s o f t e n i n g . NBC moldings are p r o duced by the r e a c t i o n i n j e c t i o n molding (RIM) of polypropylene g l y c o l and caprolactam i n the presence of a c a t a l y s t . The t e n dency f o r t h i s copolymer to s w e l l i n the presence of water i s reduced by r e i n f o r c i n g w i t h g l a s s f i b e r s . Nylon-6 which has a heat d e f l e c t i o n temperature of 80°C was produced by the r i n g opening p o l y m e r i z a t i o n of caprolactam i n Germany i n the 1940 s.(A2)Molded a r t i c l e s of these polymers may be produced i n s i t u i n the RIM process. C 1 2 ) N y l o n - l l and nylon-12 produced by the a n i o n i c p o l y m e r i z a t i o n of 11 and 12-amino a c i d s are a l s o c h a r a c t e r i z e d by good r e s i s t a n c e to moisture and s u p e r i o r d u c t i l i t y . The s t r u c t u r e of the r e p e a t i n g u n i t i n monadic n y l o n s , such as nylon-6 i s : 1

H

0

I

I!

TN-(CH-)

l a-1

-C}

where a i s the number of carbon atoms i n the r e p e a t i n g u n i t . The copolymer of nylon-6 and nylon-66 i s tougher and has a smoother s u r f a c e than e i t h e r of the homopolymers. I n j e c t i o n moldable, y e l l o w , transparent polyamide (PA7030) is also available.(14)

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7. SEYMOUR

91

High-Performance Polymers

The aromatic polyamides (aramids) have been produced by the i n t e r f a c i a l condensation of aromatic diamines, such as 1, 3-phenylenediamine and i s o p h t h a l o y l c h l o r i d e i n c h l o r o f o r m . Amorphous transparent aramids w i t h heat d e f l e c t i o n temperatures of 160 C have been produced from 2 , 2 - b i s - 4 - ( a m i n o c y c l o h e x y l ) propane.(15) T y p i c a l polyamides w i l l have the f o l l o w i n g p r o p e r t i e s : Nylon-66 Nylon-6 PA7030 Aramid t e n s i l e strength (psi) 12,000 18,000 11,000 17,500 e l o n g a t i o n (%) 60 50 8 55 f l e x u r a l strength (psi) 17,000 14,000 15,000 26,000 f l e x u r a l modulus ( p s i ) 420,000 390,000 640,000 i z o d impact ( f t l b s / i n of notch) 1.0 1.0 4.2 1.5 Rockwell hardness R120 R119 M93 m e l t i n g p o i n t (°C) 26 d e f l e c t i o n temperature (°C Polycarbonates The polycarbonates were discovered independently by S c h n e l P — a n d Fox ^—In the 1 9 5 0 s . These tough engineering p l a s t i c s are now produced at an annual r a t e of 130 thousand tons i n the U.S. I t i s estimated that the annual production of these high performance p l a s t i c s i n the l a t e 1980 s w i l l be 250 thousand tons. Polycarbonate and p o l y c a r b o n a t e - p o l y e s t e r copolymers are being used f o r g l a z i n g , sealed beam h e a d l i g h t s , door s e a l s , popcorn cookers, s o l a r heat c o l l e c t o r s and a p p l i a n c e s . The s t r u c t u r e of the r e p e a t i n g u n i t i n PC i s f

f

Polycarbonate (PC) tends to s t r e s s crack i n the presence of g a s o l i n e but a 50-50 blend w i t h p o l y b u t y l t e r e p h t h a l a t e (PBT, Xenoy) i s u n u s u a l l y r e s i s t a n t to g a s o l i n e . 12) The p r o p e r t i e s of t y p i c a l polycarbonates are as f o l l o w s :

t e n s i l e strength (psi) e l o n g a t i o n (%) f l e x u r a l strength (psi) f l e x u r a l modulus ( p s i ) i z o d impact ( f t l b s / i n of notch) Rockwell hardness m e l t i n g p o i n t (°C) d e f l e c t i o n temperature (°C)

unfilled

30% g l a s s f i l l e d

9,500 110 13,500 340,000 16 M70 150 120

19,000 4 23,000 1,250,000 2 M92 tg=150 140

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Polyfluorocarbons P o l y t e t r a f l u o r o e t h y l e n e (PTFE Teflon) was discovered a c c i d e n t l y by PlunkettO^Xand commercialized by DuPont i n the 1 9 4 0 s . This polymer has a s o l u b i l i t y parameter of about 6H and a high m e l t i n g point of 327°C and i s not r e a d i l y moldable. Polyc h l o r o t r i f l u o r o e t h y l e n e (CTFE, K e l - F ) , the copolymer of t e t r a f l u o r o e t h y l e n e and hexafluoropropylene (FEP), p o l y v i n y l i d e n e f l u o r i d e (PVDF, Kynar), the copolymer of t e t r a f l u o r o e t h y l e n e and ethylene (ETFE), the copolymer of v i n y l i d e n e f l u o r i d e and hexaf l u o r o i s o b u t y l e n e (CM-1), p e r f l u o r o a l k o x y e t h y l e n e (PFA) and p o l y v i n y l f l u o r i d e (PVF, Tedlar) are a l l more r e a d i l y processed than PTFE. However, the l u b r i c i t y and chemical r e s i s t a n c e of these fluoropolymers i s l e s s than that of PTFE. The s t r u c t u r e of the r e n e a t i n g u n i t i n PTFE i s f

t c - c -}

The p r o p e r t i e s of t y p i c a l fluoropolymers are shown below:

t e n s i l e strength ( p s i ) e l o n g a t i o n (%) f l e x u r a l strength (psi) f l e x u r a l modulus ( p s i ) i z o d impact ( f t l b s / i n of notch) Rockwell hardness m e l t i n g point (°C) d e f l e c t i o n temperature (°C) (66psi) Polyphenylene

PTFE

FEP

3,000 200

2,800 250

60,000 13 327

PVDF 6,000 100 900 20,000 4

D60 275

156 80

120

oxide

I n j e c t i o n moldable polyphenylene oxide (PPO, Noryl) was produced by A. S . Hay i n the e a r l v I 9 6 0 s by the copper-amine c a t a l y z e d o x i d a t i o n of x y l e n o l s . ( 2 1 ) T h e commercial product i s a blend of PPO and p o l y s t y r e n e . PPO i s being produced at an annual r a t e of 70 thousand tons i n the U . S . and i t i s a n t i c i p a t e d that the annual production i n the l a t e 1980*s w i l l exceed 175 thousand t o n s . The s t r u c t u r e of the r e p e a t i n g u n i t i n PPO i s 1

0

+

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7. SEYMOUR

93

High-Performance Polymers

PPO extruded sheet i s being used f o r s o l a r energy c o l l e c t o r s , l i f e guards on broadcasting towers, a i r l i n e beverage cases and window frames. The p r o p e r t i e s of a t y p i c a l PPO-PS blend are as f o l l o w s : 30% g l a s s PPO-PS filled t e n s i l e strength (psi) 9,500 e l o n g a t i o n (%) 60 f l e x u r a l strength (psi) 13,000 f l e x u r a l modulus ( p s i ) 355,000 i z o d impact ( f t l b s / i n of notch) 5 Rockwell hardness R115 g l a s s t r a n s i t i o n temperature (Tg) 135 d e f l e c t i o n temperature (°C) 120 Polyphenylene

18,000 4 21,000 20,000,000 2 R115 105 130

sulfide

Polyphenylene s u l f i d e (Ryton) i s produced by a Wurtz F i t t i g r e a c t i o n of p-dichlorobenzene and sodium s u l f i d e . (22)This high m e l t i n g (290°C) c r y s t a l l i n e polymer may be i n j e c t i o n molded or processed as a powder by compacting, s i n t e r i n g and f o r g i n g . The c o m p r e s s a b i l i t y of the polymeric powder i s improved by the a d d i t i o n of PTFE f i l l e r . PPS moldings may be c r o s s l i n k e d by h e a t i n g at temperatures above 370°C. PPS i s used at an annual r a t e of about 2,000 tons but i s a n t i c i p a t e d that t h i s r a t e w i l l i n c r e a s e to 25 thousand tons i n the l a t e 1 9 8 0 s . This polymer i s being used f o r pumps, sleeve b e a r i n g s , cookware, quartz halogen lamp p a r t s and e l e c t r i c a l appliances.(23) The s t r u c t u r e of the r e p e a t i n g u n i t i n PPS i s f

The p r o p e r t i e s of t y p i c a l PPS molded products are as f o l l o w s : PPS t e n s i l e strength (psi) 9,500 e l o n g a t i o n (%) 1 f l e x u r a l s t r e n g t h ( p s i ) 14,000 f l e x u r a l modulus ( p s i ) 550,000 i z o d impact ( f t l b s / i n of notch) Rockwell hardness R123 m e l t i n g point (°C) 290 d e f l e c t i o n temperature (°C) 135

PPS w i t h 40% g l a s s 19,500 1 29,000 1,700,000 R123 290 250

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

94

Polvaryl esters Thermoset p o l y e s t e r s , such as G l y p t a l , alkyds and g l a s s r e i n f o r c e d unsaturated p o l y e s t e r s have been a v a i l a b l e f o r s e v e r a l decades but i n j e c t i o n moldable p o l y a r y l e s t e r s are r e l a t i v e l y new. W h i n f i e l d and Dickerson extruded polyethylene t e r e p h t h a l a t e (PET) f i b e r s (Dacron) i n the 1 9 4 0 s . (24)pET was a l s o extruded as f i l m (Mylar) i n the 1950 s but t h i s polymer was not blow molded commercially u n t i l the 1 9 7 0 s . ' The a d d i t i o n of a n t i n u c l e a t i n g agents permits the i n j e c t i o n molding of PET ( R y n i t e ) . I n j e c t i o n moldable g l y c o l - m o d i f i e d p o l y e s t e r s (PETG, Kodar) have been produced by p a r t i a l r e p l a c e ment of the ethylene g l y c o l by cyclohexanol d i m e t h y l o l . The s t r u c t u r e of the r e p e a t i n g u n i t i n PET i s f

f

f

M o l d a b i l i t y of a r y l p o l y e s t e r s have a l s o been improved by the use of polybutylene t e r e p h t h a l a t e (PBT) i n s t e a d of PET or by the use of blends of PET and PBT. PBT under the trade name of Celanex, V a l o x , G a f i t e and V e r s e l i s being produced at an annual r a t e of 25 thousand t o n s . Copolymers of carbonate and a r y l e s t e r s , a c r y l i c s and a r y l e s t e r s , and imide and a r y l e s t e r s as w e l l as p h y s i c a l blends of p o l y e s t e r s and other polymers are a v a i l a b l e . These a r y l p o l y e s t e r s are being used f o r b i c y c l e wheels, s p r i n g s , and blow molded c o n t a i n e r s . The p r o p e r t i e s of t y p i c a l a r y l p o l y e s t e r s are as f o l l o w s :

t e n s i l e strength (psi) e l o n g a t i o n (%) f l e x u r a l strength (psi) f l e x u r a l modulus ( p s i ) i z o d impact ( f t l b s / i n of notch) Rockwell hardness m e l t i n g p o i n t (°C) d e f l e c t i o n temperature (°C)

PET 8,500 50 14,000 350,000

PBT 8,500 50 12,000 300,000

0.3 M94 245 50

0.8 M70 235 40

PBT 30% glass 12,000 4 26,000 1,100,000 1.5 M90 245 105

A new h i g h impact blend of PBT and polybutene (Valox CT) i s also available, melt v i s c o s i t y of blends of PET and nylon-66 has been reduced by the a d d i t i o n of p o l y v i n y l a l c o h o l . S e l f r e i n f o r c i n g PET has been produced by the a d d i t i o n of phydroxybenzoic a c i d which forms l i q u i d c r y s t a l s i n the composite.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7. SEYMOUR Polyaryl

High-Performance Polymers

95

suIfones

There are s e v e r a l types of p o l y a r y l sulfones a v a i l a b l e commercially. The c l a s s i c p o l y s u l f o n e (U&el) was produced by the n u c l e o p h i l i c displacement of the c h l o r i n e s u b s t i t u e n t s on b i s ( p - c h l o r o p h e n y l ) sulfone by the sodium s a l t of b i s p h e n o l A.(?lDAnother p o l y s u l f o n e ( A s t r e l ) i s produced by the F r i e d e l C r a f t s condensation of biphenyl with oxy-bis(benzene s u l f o n y l c h l o r i d e ) . Another p o l y s u l f o n e ( V i t r e x ) , i s produced by the a l k a l i n e condensation of b i s ( c h l o r o p h e n y l ) sulfone.(28)Blends of p o l y s u l f o n e s with ABS (Arylon, Mindel) and SAN (Ucardel) are available. P o l y s u l f o n e s which a r e produced at an annual r a t e o f 20 thousand tons a r e being used f o r i g n i t i o n components, h a i r d r i e r s , cookware and s t r u c t u r a l foams. The s t r u c t u r e of th sulfone i s

+oThe p r o p e r t i e s

of

typical polyaryl

sulfones

are

as

follows : Polyaryl Sulfone

t e n s i l e strength ( p s i ) elongation (%) f l e x u r a l strength ( p s i ) f l e x u r a l modulus ( p s i ) i z o d impact ( f t l b s / i n of notch) Rockwell Hardness g l a s s t r a n s i t i o n temp. (°C) d e f l e c t i o n temperature (°C)

6,500 50 15,000 360,000 1.2 M69 190 175

P o l y a r y l Sulfone +30% F i b e r g l a s s 15,000 2 30,000 1,350,000 1.1 M90 185

Gruman has developed an automated t r i a n g u l a r t r u s s - t y p e beam b u i l d e r using g r a p h i t e - r e i n f o r c e d polyether s u l f o n e . T h i s beam can be formed i n outerspace at the r a t e of 1.5m per min. from f l a t stock which i s heated and forced continuously around a d i e . The s e c t i o n s are i n d u c t i o n welded and may be p r o t e c t e d from d e t e r i o r a t i o n by the a p p l i c a t i o n of a c o a t i n g of polyether ether ketone (PEEK).(30) Polyether ether ketone ICI has introduced a new c r y s t a l l i n e polyether ether ketone

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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(PEEK), which has a g l a s s t r a n s i t i o n temperature of 145°C and a heat d e f l e c t i o n temperature f o r r e i n f o r c e d PEEK of 300°C.(31)PEEK i s being considered f o r use as blow molded c o n t a i n e r s f o r n u c l e a r wastes, j e t engine components, p r i n t e d c i r c u i t s , e l e c t r i c a l a p p l i c a t i o n s and wire c o a t i n g s . (32) The s t r u c t u r e of the r e p e a t i n g u n i t i n PEEK i s

Polyimides Heat r e s i s t a n t i n t r a c t a b l e thermoset polyimides (Vespel, K i n e l , Kapton) have been supplemented by i n j e c t i o n moldable polyamide-imides (Torlon) and modified polyimides (Kanox, Toramid) . (^.^Thermoplastic polyimide adhesives were c i t e d as one of the top 100 i n v e n t i o n s i n 1981. Polyimide foam does not i g n i t e at temperatures below 430°C and i s being considered as a cushioning m a t e r i a l i n p u b l i c conveyances. The s t r u c t u r e of the r e p e a t i n g u n i t i n polyimide i s

ο

ο

The p r o c e s s i n g p r o p e r t i e s are improved when polyimides are produced from meta s u b s t i t u t e d diamines.(^-t^A new amorphous polyether-imide (Ultem) with a h i g h heat d e f l e c t i o n temperature has been introduced by the General E l e c t r i c Co. The ether l i n k a g e s i n PEI improve the ease of processing and i n c r e a s e the d u c t i l i t y of these high performance p l a s t i c s . Q i ) PEI r e i n f o r c e d with 30% f i b e r g l a s s has a heat d e f l e c t i o n tem­ perature of 2 1 0 o c . ( l i ) The polyamide-imide ( T o r l o n , PA-1) has a heat d e f l e c t i o n temperature of 285°C. A Ford automobile prototype engine has been b u i l t from PA-1. (1Z.» 38)

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

7. SEYMOUR

97

High-Performance Polymers

Conclusions In s p i t e of t h e i r u t i l i t y and v e r s a t i l i t y , the new h i g h performance polymers w i l l not d i s p l a c e g e n e r a l purpose thermo­ p l a s t i c s , c l a s s i c thermosets, ceramics or metals u n l e s s there i s a demonstratable s u p e r i o r i t y . F o r t u n a t e l y , there are many a p p l i c a t i o n s f o r h i g h performance t h e r m o p l a s t i c s f o r which no other m a t e r i a l i s adequate. Hence, the annual p r o d u c t i o n of high performance t h e r m o p l a s t i c s i n the l a t e 1980 s w i l l exceed the p r o d u c t i o n of a l l p l a s t i c s i n the 1940*s. T h i s unprecedented growth of these engineering polymers w i l l be based e n t i r e l y on t h e i r performance. f

Literature Cited

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25.

Seymour, R.B., Ed Caulking Compounds" American Chemical Society: Washington, DC, 1979. Seymour, R.B., Ed. "Additives for Plastics"; Vols I and II, Academic Press: New York, 1978. Seymour, R.B.; Kispersky, J.P.; U.S. 2,439,227 Seymour, R.B., Ed. "History of Polymer Chemistry"; Marcel Dekker: New York, 1982. McDonald, R.N.; U.S. 2,768,994 Walling, C.; Brown, F.; Bartz, K.W.; U.S. 3,027,352 Seymour, R. Β.; "Plastics vs Corrosives"; John Wiley and Sons: New York, 1982. Carothers, W.H.; U.S. 2,130,947 Garshman, A. Plast Technol, 1978, 24(11), 79. Swanson, D.E. Plast Des and Proc, 1978, 17(5), 44. Wood, A.S. Modern Plastics, 1982, 58(8), 46. Reinschuessel, H. J. J. Poly Sci/Macromolecules, 1977, 12, 65. Riley, M. W. Plast Technol, 1979, 25(4), 11. Riley, M. W. Plast Technol, 1982, 28(6), 15. Hill, R. Polym Eng Sci, 1978, 18, 36. Schnell, H. Angew Chemie, 1956, 68(2), 633. Fox, D. W.; Chap 310 "Applied Polymer Science"; Craver, J.K. and Tess, R.W. Eds. American Chemical Society: Washington, DC, 1975. Riley, M. W. Plast Technol, 1982, 28(6), 29. Gross, S. Modern Plastics, 1982, 59(6), 34. Plunkett, R.J.; U.S. 630,654. Fox, D. W.; Chap 30 "Applied Polymer Science"; Craver, J.K. and Tess, R. W. Eds. American Chemical Society: Washington, DC, 1975. Bolke, P. U. U.S. Dix Plast Eng, 1982, 38(2), 25. Edmunds, J.T.; Hill, H. W.; U.S. 3,334,129. Whinfield, J. R. Nature, 1945, 138, 930. Pengilly, W. O. Modern Plastics, 1978, 55(104), 50.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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26. Gross, S. Modern Plastics, 1982, 59(2), 14, 74. 27. Leslie, V. J.; Rose, J.; Rudken, G.O.; Feltzen, J. Chem Tech, 1975, 5, 426. 28. Von Hassel, A. Plast Technol, 1980, 25, 57. 29. Steming, J.; Smith, C.P.; Kimber, P.J. Modern Plastics, 1981, 58(11), 86. 30. Riley, M. W. Plast Technol, 1981, 27(8), 139. 31. Riley, M. W. Plast Technol, 1981, 28(6), 21. 32. Riley, M. W. Plast Technol, 1981, 27(8), 139. 33. Bitterbeck, C. J. Modern Plastics, 1981, 57(10A), 46. 34. St. Clair, A.K.; St. Clair, T.L. SAMPE Quart, 1981, 13(3), 20. 35. Rimsa, S.B.; Serfaty, I.W., presented at SPE-Antec, San Francisco, CA, May 10, 1982. 36. Riley, M. W. Plast Technol, 1982, 28(3), 17. 37. Floryan, D. E.; Serfaty 59(6), 146. 38. Spaulding, L.D. Plast Eng, 1981, 28(3), 25. RECEIVED June

13, 1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

8 Model Fungicidal Monomers, Polymers, and Latices for Paints CHARLES U. PITTMAN, JR. Chemical Consultant, 132 Woodland Forrest, Tuscaloosa, A L 35405 G. A L L A N STAHL Phillips Petroleum Company, Research and Development, Bartlesville, OK 74004

Summary

When a biocide is simply mixed into a paint it may subse­ quently be lost from the painted surface by leaching or vapori­ zation. To overcome this problem several biocidal compounds have been converted to vinyl monomers and subsequently incorpor­ ated into homo-, co-, and terpolymers. Latices have been pre­ pared for several systems. Since mildew defacement of painted surfaces is widespread problem, we have concentrated on polymer anchoring of fungicidal compounds and compounds with wide bio­ cidal activity. These included pentachlorophenol, 8-hydroxyquinoline, 2-(4'-thiozoyl)benzimidazole, 3,4',5-tribromosalicylanilide, o-benzyl-p-chlorophenol, o-acrylyl salicylanilide and 2-mercapto-pyridine-N-oxide. The reactivity ratios of the bio­ cidal monomer, pentachlorophenyl acrylate, were obtained with both vinyl acetate and ethyl acrylate. While it is possible that some biocides may function when incorporated into a macromolecule, it seems likely that many biocides must be released from the polymer to be active. Thus, the biocidal monomers were incorporated into the polymers using functions with different hydrolytic propensities. These included, fungicidal acrylates, 2-fungicidalethyl acrylates, and fungicidal vinyl ethers. The polymerization behavior of several such monomers was examined. S t a b l e terpolymer l a t i c e s were prepared from methyl methacrylate, η-butyl a c r y l a t e and each o f the f o l l o w i n g f u n g i c i d a l monomers: (1) pentachlorophenyl a c r y l a t e , (2) 2-pentachlorophenoxyethyl a c r y l a t e , (3) 2 - ( 8 - q u i n o l i n y l o x y ) e t h y l a c r y l a t e , (4) a c r y l o y l o x y 3 , 4 , 5 - t r i b r o m o s a l i c y l a n i l i d e , (5) 2 - ( 2 - a c r y l o y l e t h o x y ) - 3 , 4 , 5 t r i b r o m o s a l i c y l a n i l i d e , (6) 2-(o-benzyl-p-chlorophenoxy)ethyl a c r y l a t e and (7) v i n y l o-benzyl-p-chlorophenyl ether. A t e r ­ polymer l a t e x o f v i n y l a c e t a t e , 2-ethylhexyl a c r y l a t e and a c r y l o y l o x y - 3 , 4 , 5 - t r i b r o m o s a l i c y l a n i l i d e was made. A l a t e x c o n t a i n i n g pentachlorophenol bound by two d i f f e r e n t r e l e a s i n g groups and a l a t e x with two d i f f e r e n t f u n g i c i d a l monomers was made. 1

1

f

0097-6156/83/0229-0099$10.75/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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A c c e l e r a t e d growth t e s t i n g of monomers, polymers, and l a t i c e s c o n t a i n i n g chemically bound f u n g i c i d e s demonstrated that the concept of polymer-anchoring b i o c i d e s has promise. Several systems were shown to c o n t r o l microorganism growth i n minimum i n h i b i t o r y c o n c e n t r a t i o n t e s t s using both agar d i l u t i o n and aqueous n u t r i e n t broath methods. A v a r i e t y of i n v i t r o agar d i s h growth t e s t s and the "Zabel T e s t " were a l s o employed. Photochemical cleavage of b i o c i d e from some polymers was demonstrated i n UV i r r a d i a t i o n agar d i s h t e s t s . Taken together the r e s u l t s provide l a b o r a t o r y support f o r the concept that binder polymers, c o n t a i n i n g chemically bound b i o c i d e s , can be u s e f u l f o r c o n t r o l l i n g microorganism growth. Introduction Mercury-containing to the high t o x i c i t y o Since mercury s a l t s have been widely used f o r b a c t e r i a l and fungal c o n t r o l i n p a i n t s more acceptable replacements have been i n c r e a s i n g l y sought i n recent years. A research program sponsored by the Paint Research I n s t i t u t e at the U n i v e r s i t y of Alabama was undertaken to look f o r organic b i o c i d e s which could r e p l a c e mercury s a l t s . Since organic compounds may l e a c h or v a p o r i z e from t h i n , high s u r f a c e area p a i n t f i l m s , the focus of the Alabama program became the development of polymer-anchored f u n g i c i d e s . A d e t a i l e d l i t e r a t u r e search* i n 1976 revealed that l i t t l e work had been done with t h i s concept i n connection with outdoor coatings except f o r some s t u d i e s of t r i a l k y l t i n e s t e r s ^ . D r i s c o and coworkers^"^ prepared p a i n t r e s i n s c o n t a i n i n g t r i - n b u t y l t i n a c r y l a t e . Laboratory t e s t s i n d i c a t e d these r e s i n s were r e s i s t a n t to Aureobâsidium p u l l u l a n s , A s p e r g i l l u s n i g e r , and A s p e r g i l l u s oryzae, and that f u n g i c i d e l e a c h i n g from the c o a t i n g was c o n s i d e r a b l y reduced compared to the use of the blended f u n g i c i d e . However, f i e l d t e s t s of these coating resins^»^ on pine and redwood t e s t panels began to show microorganism growth a f t e r three months. Mildew defacement of organic coatings has long been a major problem of the p a i n t i n d u s t r y . Aureobasidium p u l l u l a n s i s the major c a u s i t i v e organism r e s p o n s i b l e f o r t h i s defacement.6»7 A current approach to solve t h i s problem i s to blend a f u n g i c i d e i n t o the p a i n t formulation. Although t h i s s o l u t i o n has had success f o r short time p e r i o d s , the f u n g i c i d e tends to be vapori z e d or leached from the c o a t i n g over long time p e r i o d s . After the c o n c e n t r a t i o n of f u n g i c i d e drops below c r i t i c a l l e v e l s , mildew may s t a r t growing on the coatings surface.** Several f a c t o r s must be considered i n s e l e c t i n g a f u n g i c i d e f o r blending i n t o paints.9 The four most important f a c t o r s , other than c o s t , are t o x i c i t y , s o l u b i l i t y , v o l a t i l i t y , and UV

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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stability. T o x i c i t y t o f u n g i and b a c t e r i a must be h i g h , b u t t o x i c i t y t o humans s h o u l d be l o w . The s o l u b i l i t y o f any c a n d i d a t e f u n g i c i d e must be c a r e f u l l y c o n s i d e r e d f o r s e v e r a l reasons. The f u n g i c i d e must n o t be w a t e r s o l u b l e s i n c e i t w o u l d l e a c h from c o a t i n g s d u r i n g r a i n . Even a s l i g h t water s o l u b i l i t y e l i m i n a t e s many f u n g i c i d e s f o r s e l e c t i o n i n p a i n t s . A l s o , the f u n g i c i d e n e e d s t o be s o l u b l e i n t h e p a i n t o r t o be d i s p e r s e d without s e t t l i n g or agglomerating. I f the f u n g i c i d e agglomera t e s , d i s p e r s i n g a g e n t u s e i n t h e p a i n t may be r e q u i r e d l e a d i n g t o f o r m u l a t i o n c o m p l i c a t i o n s and h i g h e r c o s t s . Fungicides with a p p r e c i a b l e v a p o r p r e s s u r e s c a n n o t be c o n s i d e r e d f o r p a i n t u s e s i n c e they would v a p o r i z e from the p a i n t a f t e r a p p l i c a t i o n to a surface. U l t r a v i o l e t p h o t o d e c o m p o s i t i o n may d e g r a d e c e r t a i n f u n g i c i d e s and s u c h f u n g i c i d e s must be a v o i d e d . The concept of polymer-anchorin advantages. V o l i t i l e biocide w o u l d be c h e m i c a l l y a t t a c h e d t o t h e p a i n t b i n d e r . Water-soluble b i o c i d e s a l s o may be c o n s i d e r e d s i n c e t h e p o l y m e r t h e y w o u l d be a n c h o r e d t o w o u l d be w a t e r i n s o l u b l e . The p o l y m e r - a n c h o r e d b i o c i d e w o u l d be m o l e c u l a r l y d i s p e r s e d t h r o u g h o u t t h e f i l m r a t h e r than present i n s m a l l p a r t i c l e s . S i n c e the b i o c i d e would r e m a i n w i t h i n t h e f i l m l o n g e r i f i t were p o l y m e r a n c h o r e d , a l o w e r l e v e l o f b i o c i d e i n c o r p o r a t i o n i n t h e p a i n t m i g h t be possible for a given useful mildewcidal l i f e t i m e . A l s o , the a n c h o r e d b i o c i d e s w o u l d be l e s s t o x i c t o humans w h i c h may p e r m i t t h e u s e o f c e r t a i n compounds w h i c h o t h e r w i s e w o u l d be a v o i d e d . H o w e v e r , w i t h t h e s e a d v a n t a g e s come s e v e r a l p o t e n t i a l p r o b l e m s . The p o l y m e r i z a t i o n o f p o t e n t i a l b i o c i d a l monomers c o u l d be troublesome. The i n c o r p o r a t i o n o f s u c h monomers i n t o t h e p o l y mer w o u l d h a v e t o be k e p t a t low m o l e p e r c e n t s t o a v o i d c h a n g i n g s u b s t a n t i a l l y the p o l y m e r ' s p r o p e r t i e s ( i . e . , T g , e t c . ) . Proper d e s i g n o f c o p o l y m e r s o r t e r p o l y m e r s c o u l d overcome t h i s p r o b l e m . A fundamental q u e s t i o n i n v o l v e s the b i o c i d a l a c t i v i t y o f t h e b i o c i d e when i t i s c h e m i c a l l y a t t a c h e d t o a p o l y m e r . Will t h e p o l y m e r be an a c t i v e b i o c i d e ? I f the b i o c i d a l a c t i v i t y r e s u l t s f r o m an i n t e r a c t i o n o f t h e b i o c i d e a t t h e c e l l w a l l o r by i n a c t i v a t i n g an e x o c e l l u l a r enzyme, t h e n i t i s p o s s i b l e t h a t t h e p o l y m e r , i t s e l f , c o u l d be an a c t i v e b i o c i d e . However, i f the b i o c i d e must be i n c o r p o r a t e d i n t o t h e o r g a n i s m t o f u n c t i o n , t h e n i t w i l l h a v e t o be c l e a v e d f r o m t h e p o l y m e r b i n d e r p r i o r t o exhibiting activity. F o r that reason polymers h a v i n g b i o c i d e s a t t a c h e d by f u n c t i o n a l g r o u p s o f d i f f e r i n g h y d r o l y t i c s u s c e p t a b i l i t y were made. D e s i g n o f p o l y m e r - b o u n d f u n g i c i d e s c a n accommodate a s l o w r e l e a s e mechanism o r a p e r m a n e n t l y a t t a c h e d b i o c i d e . The c h e m i cal l i n k a g e s used to a t t a c h f u n g i c i d e s to polymers c o u l d e i t h e r be h y d r o l y z a b l e o r n o n h y d r o l y z a b l e d e p e n d i n g on t h e t y p e c h e m i c a l

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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bonding used. E s t e r or amide l i n k a g e s , which undergo a c i d - , b a s e - , or enzyme-catalyzed h y d r o l y s i s , may be used to bind the f u n g i c i d e and, t h e r e f o r e , l a t e r r e l e a s e the free f u n g i c i d e upon cleavage of that l i n k a g e . These l i n k a g e s could be designed to cleave at v a r i o u s r a t e s under environmental c o n d i t i o n s (or by the enzymes released by microorganisms). I f environmental c o n d i t i o n s cause h y d r o l y s i s of the l i n k a g e , there would be some l o s s of f u n g i c i d e due to l e a c h i n g , but the r a t e of l e a c h i n g could be f a r l e s s than the l e a c h i n g r a t e of that same f u n g i c i d e i f i t were simply blended i n t o the p a i n t . Many f u n g i c i d e s might f u n c t i o n to r e t a r d growth only a f t e r they have been released from the c o a t i n g , but t h i s may not be true of a l l f u n g i c i d e s . Once r e l e a s e d from the polymer, the c o n c e n t r a t i o n of free f u n g i c i d e s might be too low to achieve the d e s i r e d r e s u l t . Nonhydrol y z a b l e l i n k a g e s , such as ether or hydrocarbon bonds, could a l s o be used. These l i n k a g e s would stop mildew growth only i f the fungicide i s s t i l l activ our knowledge, no s t u d i e s of f u n g i c i d e s bound to polymers by these types of linkages have been done. Slow r e l e a s e h e r b i c i d e s which use the polymer-anchoring concept have been developed. Over the past few years s e v e r a l b i o c i d e s have been converted to monomers c o n t a i n i n g e s t e r , amide, or ether f u n c t i o n s which bind the b i o c i d e and the p o l y m e r i z a t i o n of these monomers was studied.12-16 ^ b i o c i d e s examined included pentachlorophenol, 1^12-16 8 - h y d r o x y q u i n o l i n e , 2 , ^ » 14-16 3 , 4 , 5 - t r i b r o m o s a l i c y l a n i l i d e , 3 , * 2 , 14-16 o-benzyl-p-chlorophenol,4,14"16 s a l i c y lanilide,5,*2 2-(4'-thiazoyl)benzimidazole,6, i 2-mercaptopyridine-N-oxide,7. e

1

a n (

OH

OH

CI

Pentachlorophenol

8-Hydroxyquinoline

1

2 OH

0

CI

Br

3,4», 5-Tribromosalicylanilide 3

o-Benzyl-p-chlorophenol 4

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Fungicides for Paints

OCK) H 2-(4

f

-thiazoyDbenzimidazole 6

0"

fa" 2-Mercaptopyridine-N-oxide Pentachlorophenol was chosen because i t i s a broad spectrum b i o c i d e w i d e l y used as a wood p r e s e r v a t i v e and as a slime c o n t r o l agent.17-20 8-Hydroxyquinoline had been used as a f u n g i c i d e before 1900 and i s thought to f u n c t i o n by c h e l a t i n g metal i o n s . ^ 1 - 2 3 T r i b r o m o s a l i c y l a n i l i d e i s an a c t i v e b i o c i d e w i t h low d e r m a t o l o g i c a l e f f e c t s to humans.24-26 j biocidal effects vary upon the a d d i t i o n of s u r f a c t a n t s to i t s m e d i u m . ^ » * oBenzyl-p-chloroDhenol i s known to be a broad spectrum commercial b a c t e r i a c i d e ^ ^ 2 8 but i t s f u n g i c i d a l p r o p e r t i e s have not been published. 2-(4 -thiazoyDbenzimidazole i s a fungicide, produced by Merck I n c . , which has been used i n p a i n t s . Due to i t s n o n v o l i t i l i t y and low s o l u b i l i t y 6^ can be mixed w i t h p a i n t s and remain i n the f i l m . 2-Mercaptopyridine-N-oxide i s a f u n g i c i d e produced by O l i n Inc. and used w i d e l y i n shampoos as an a n t i dandruff agent. Results t

s

J

u

s

f

Monomer P r e p a r a t i o n Each of the f u n g i c i d e s , 1-5 has a phenolic hydroxy group. Therefore, the a c r y l i c e s t e r s of each are r e a d i l y prepared. However, the s t a b l e phenoxide anions of 1-5 are good l e a v i n g groups. Thus, these a c r y l i c e s t e r s or t h e i r polymers should undergo reasonably f a c i l e h y d r o l y s i s . For t h i s reason, polymers of these a c r y l a t e s should be able to r e l e a s e the s p e c i f i c b i o c i d e as shown i n Scheme I. The h y d r o l y s i s of 8-hydroxyquinoline e s t e r s i s p a r t i c u l a r l y r a p i d due to neighboring group p a r t i c i p a t i o n of n i t r o g e n . * 2 , 1 To provide a s e r i e s of monomers (polymers) which would hyd r o l y z e more s l o w l y than the above-mentioned p h e n o l i c a c r y l a t e s , the p h e n o l i c group was f i r s t converted to i t s 2-hydroxyethyl ether d e r i v a t i v e which, i n t u r n , was converted to i t s correspond ing chain-extended a c r y l a t e (see Scheme I I ) . Ester hydrolysis

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

104

of these chain-extended e s t e r s r e l e a s e s an alkoxide anion which i s a stronger base, hence a poorer l e a v i n g group, than phenoxy anions. Thus, p o l y a c r y l a t e s o f these monomers should r e l e a s e the b i o c i d a l moiety more slowly than the phenolic p o l y a c r y l a t e s . Further, i t should be noted that the 2-hydroxyethyl ether of the o r i g i n a l f u n g i c i d e i s r e l e a s e d . T h i s may be b i o l o g i c a l l y i n a c t i v e or l e s s a c t i v e than i t s parent f u n g i c i d e ( i . e . 1-5). These ethers may (or may not) have to f u r t h e r degrade back to the parent f u n g i c i d e to d i s p l a y f u n g i c i d a l a c t i v i t y . Binder polymers c o n t a i n i n g both the a c r y l a t e and chain extended acryl a t e s might e x h i b i t extended p r o t e c t i o n against mildew defacement . A f u r t h e r task was the c o n s t r u c t i o n o f polymers from which a bound f u n g i c i d e would not h y d r o l y z e . Since a r y l secondary a l k y l ethers are only cleave s e l e c t e d the v i n y l ether A disadvantage recognized at the outset was the expected d i f f i c u l t y of copolymerizing v i n y l ethers (which undergo ready c a t i o n i c p o l y m e r i z a t i o n ) with a c r y l i c monomers which are polymerized using r a d i c a l or a n i o n i c i n i t i a t o r s but which r e s i s t c a t i o n i c i n i t i a t i o n (Scheme I I I ) . 2

A l l o f the a c r y l a t e and chain-extended a c r y l a t e synthèses* » 14-16 summarized i n Scheme IV together with y i e l d s . Scheme IV a l s o i l l u s t r a t e s the route that was u s e d * to convert 6^ to i t s acylamide analog 2-(4'-thiazoyDbenzimidazoyl acrylate,21· This monomer polymerizes to give polymers* which undergo f a c i l e h y d r o l y s i s to free 6^ because the 2 - ( 4 * - t h i a z o y D b e n z i m i d a z o l y l l e a v i n g group i s a s t a b l e anion (by v i r t u e of resonance s t a b i l i z a t i o n of negative charge by the benzimidazole r i n g ) . This ready h y d r o l y s i s was i l l u s t r a t e d by the i n a b i l i t y to prepare the monomer on treatment of 6^ with a c r y l o y l c h l o r i d e * - . Thus, the sodium s a l t of 6^ was made and reacted with a c r y l o y l c h l o r i d e but even t h i s method r e s u l t e d i n l o s s e s on work up and a poor o v e r a l l y i e l d (16-177o) of 2 1 . a

r

e

2

2

2

1 2

SCHEME I R-OH + CH CHC0C1

> R0C-Cft=CH

2

2

0 1-4 R = a r y l

I

ROH + —(-CHCH —)•< y o l y t i s COOH 2

h

d r

polymerize

" H * — CH COOR

r

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

8.

PITTMAN AND STAHL

Fungicides for Paints

105

SCHEME I I

R—OH

> ROCH CH OH 2

» ROCH CH OCCH—CH

2

2

2

2

I

1-4 R = a r y l

I polymeri2

HOCH CH OR + H-CHCH ->2

2

2

^

n

^

^ + CHCH -+

y

2

n

COOCH CH OR

COOH

2

2

ROH

R—OH

>R-OCH=CH

Ρ

2

θ

1

^

β

Γ

ί

ζ

β

> ^-CHCH ^ 2

n

OR

1-4 R = a r y l

hydrolyze

SCHEME IV

OH Cl

Cl

ΟΙ

Cl

Θ

Θ

• ^

:

CH9=CHC0C1

c

E t N Y - 81%

l

C

H

2

=

=

CH-cf

N

3

Cl °° C1CH CH 0H NaOH, Y=65% 2 0 ° , 48hrs 2

0

2

Q

^Z&Z** Cl H2Ç =€HC0C1 Et N, Et 0 D. C l Y=90% 3

^ °^° Λ

2

Cl

Cl

Cl N a H

OH

H C = CHC0C1 - 5 to~0° Y=89%

r

THF

e

9

H C=CHC0C1 0

ELU,—P^OT

®

Cl

©

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

106

EFFECTS OF HOSTILE ENVIRONMENTS

Q

C1CH CH 0H > NaOH, Y=70% ?

2

OCH CH OH H C-=CHC0C1

Jiv^is

il 0

^ ^j^fffo.

[

9

(12) Br

H C -CHC0C1

s Tr>

j

j»0

Br (11

ο

No R e a c t i o n NaOH υ J C IH C CHH- O0 HH - N ^ ^ X V 1— NaOH,

Br

-CHC0C1

o

© 2

2

2

B

B r ^ ^ ^ A J J^J)

CHC0 CH CH OTs, NaOH, Y=8%

H C =

IT J6T '

2

]Jr

ψ-ο-^

©

OH

H C -CHC0C1, 0° Ph 2

E t N , Y=71% 3

Θ

Cl

Cl

C17)

o —

OCH CH OH C1CH CH 0H Ph ^\Js. H C —CHCOC1 L_i_^ k E t N , Y=30% NaOH, Y=65%, 80-90 2

9

2

TJ) _2

9

0

ph

"lCl

3

CI

Jl 0

Ph

H C"CHC0C1, 15° 2

Η I

Θ Ph

E t N , Y=72% 3

0 ^

®

N

V-^S \NJ I Η

Θ

NaH DMF/BZ

60°

H C-=-CHCQCl reflux Y=16% 2

Ν

^_y/ ^ X>^^N WJ ι

©

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

0

8. PITTMAN AND STAHL

107

Fungicides for Paints

Several attempts to make the t h i o l a c r y l a t e of ]_ by t r e a t i n g _7 with a c r y o y l c h l o r i d e o r a c r y o y l anhydride f a i l e d to give the d e s i r e d product. This m a t e r i a l i s probably unstable due to the n u c l e o p h i l i c e f f e c t of the nearby oxygen on n i t r o g e n . Presumably a mixture o f r e a d i l y hydrolyzed 0- and N - s u b s t i t u t e d d e r i v a t i v e s was formed. Thus, an attempt was made to form the t h i o hemiacetal with formaldehyde. Unexpectedly, two moles o f formaldehyde condensed to g i v e hemiacetal, 22^ which was then converted to a c r y l a t e 23 (Scheme V ) . SCH 0H 2

-H-

0 t

0

+ HCHO

t

©

Et 0 CHo-CHCOCl m ?— E t N , Y=42% 2

3

SCHEME V 2

A c r y l a t e and Extended-Chain A c r y l a t e Synthesis* >14-16 The syntheses o f both a c r y l a t e and extended-chain a c r y l a t e s of f u n g i c i d e s 1-5 are summarized together with y i e l d s i n Scheme IV. A c r y l a t e s 8, 11, 14, 17, and 20 were prepared i n good y i e l d s u s i n g a c r y l o y l c h l o r i d e under normal Shotten-Baumann c o n d i t i o n s . 12,14 This method worked w e l l even f o r the s t e r i c a l l y hindered 3,4 ,5-tribromosalicylanilide. Syntheses o f chain-extended a c r y l a t e s 10, 13 and 19 were accomplished by r e a c t i n g f u n g i c i d e s 1, 2, and 4, r e s p e c t i v e l y , with 2-chloroethanol and NaOH to f i r s t generate the 2-fungicidalphenoxyethanols*^»(i.e. 9, 12 and 18). Treatment of these chain-extended a l c o h o l s with a c r y l o y l c h l o r i d e under Shotten-Baumann c o n d i t i o n s gave the chainextended a c r y l a t e s 10, 13, and 19. This route was u n s u c c e s s f u l , however, s t a r t i n g with 3 , 4 , 5 - t r i b r o m o s a l i c y l a n i l i d e because d i s placement of c h l o r i d e from 2-chloroethanol f a i l e d to g i v e the chain-extended a l c o h o l . T h e phenoxy oxygen i n 3 , 4 , 5 - t r i b r o m o s a l i c y l a n i l i d e i s s e v e r e l y hindered by the ortho bromo and amide f u n c t i o n s , and t h i s hindrance r e t a r d s the r a t e o f Sjg-2 displacement. By using 2-iodoethanol, a more r e a c t i v e s u b s t r a t e to Sjg-2 displacements, the chain-extended a l c o h o l 15 was obtained 1

f

f

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

108

a l b e i t i n low (25%) y i e l d . 1 4 E s t e r i f i c a t i o n of 15 with a c r y l o y l c h l o r i d e gave the chain-extended a c r y l a t e 16.14 The s t r u c t u r e s of each of the monomers was confirmed by i n f r a r e d and nuclear magnetic resonance spectroscopy. V i n y l Ether

Syntheses

Three general s y n t h e t i c routes were examined f o r the preparat i o n of the v i n y l ether monomers of f u n g i c i d e s 1, 3, and 4.14 These r e s u l t s are summarized i n Scheme VI. F i r s t , the 2-bromoe t h y l ethers 24, 27, and 29 were prepared from 1, 3, and 4, r e s p e c t i v e l y , v i a n u c l e o p h i l i c displacement of bromide from 1,2dibromoethane i n the presence of NaOH or KOH. Then, base-catal y z e d dehydrohalogenation gave the d e s i r e d v i n y l ether monomers 25, 28 and 30 i n s a t i s f a c t o r y y i e l d s . 1 4 A second route, based on l i t e r a t u r e precedent,29,3 phenols 1, 3, and 4 wit a c e t a t e to g i v e the v i n y l ether i n an a d d i t i o n - e l i m i n a t i o n sequence. 14 This method d i d not work on s t e r i c a l l y hindered 3 and i t gave the a c e t a l 31 (and not v i n y l ether 30) when employed with b i o c i d e 4. The t h i r d route was based on the use of 1 , 2 - v i n y l bis(triphenylphosphonium)dibromide.31 Reaction of the f u n g i c i d e s 1 and 4 with t h i s s a l t i n chloroform and t r i e t h y l a m i n e , followed by treatment with aqueous NaOH, gave v i n y l ethers 25 and 30.14 This method was not s u c c e s s f u l i n generating the v i n y l ether 28 from t r i b r o m o s a l i c y l a n i l i d e . 1 4 8-Hydroxyquinoline was r e a d i l y converted to v i n y l ether 32 i n good y i e l d s 1 4 by treatment with acetylene i n base a t e l e v a t e d temperatures and pressures u s i n g methods s i m i l a r to previous reports.32-34 Known B i o l o g i c a l A c t i v i t y of the Monomers I t i s important to consider the b i o c i d a l p r o p e r t i e s of the monomers as w e l l as the parent f u n g i c i d e s s i n c e unreacted monomer may remain i n a l a t e x a f t e r i t s p r e p a r a t i o n . Pentachlorophenyl a c r y l a t e , 8, and i t s homopolymer both i n h i b i t the growth of S. aureus, A. n i g e r , Pénicillium c i t r i n u m , and Saccharomyces cervisia?5 The polymer was l e s s a c t i v e . Poly ( v i n y l c h l o r i d e ) compositions are p r o t e c t e d a g a i n s t m i c r o b i a l a t t a c k using 8 i n concentrations of 1-2% by weight.36 2-Pentachlorophenoxyethyl bromide, 24, i s known to be f u n g i s t a t i c 3 7 d 2-pentachlorophenoxyethanol, 9, has a f a i r l y h i g h f u n g i c i d a l a c t i v i t y but i t i s l e s s t o x i c (to mice) than pentachlorophenol.37 Extended-chain a c r y l a t e 10 has not been p r e v i o u s l y r e p o r t e d . 8 - Q u i n o l i n y l a c r y l a t e , 11, has only been t e s t e d i n the c o n t r o l of A l t e r n a r i a s o l a n i on tomatoes.38,39 V i n y l - 8 - q u i n o l i n y l ether, 32, i n the form of i r o n , t i n , g o l d , and z i n c complexes were a c t i v e a g a i n s t Staphylococcus33 but not as a c t i v e as 8-hydroxyquinoline, 2. 2 - ( 8 - Q u i n o l i n y l ) e t h a n o l , 12 i s a l s o l e s s a c t i v e than 2 but was f a i r l y e f f e c t i v e a g a i n s t Staphyloccus pyrogenes and S^_ aureus.40 a n

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

8.

109

Fungicides for Paints

PITTMAN A N D STAHL

OCH2CH Br 2

C

BrCH^CH^Br OH / Clv^s^Cl

LO

U y

NaOHÎ Y=72%

C H

C H 0 A c

H

C

1

DBU, 20°,-HBr

CK^y^Cl CI

f\ ^

Y=65% Ν * . 0 ClN^k^Cl

c l

C l J \ C\C1 l ™2* - » § 2 » H S 0 , - 2 2 ° , Y=24% CI CI M \Ph3P CH=:CHP Ph 2Br7 Q.2N HBrJCfrCl OCH=CHP*Ph NaOH \U E t N , CHC1 /Os Br"" - Y=15% 2

+

4

+

3

Q

5

3

0

0 H Br

>^V^^ —

B

r

VËr ^OCH CHV 2

1

8 %

Hi

* -

\ \ V

DBU,20° Y

CH ~CH0Ac, H g C l , H S 0 ,-22° ,Y=0 2

2

2

4

y

I

l

Ph P+CH=CHP" "Phq 2Br" E t N , CHC1

Y=0

3

3

3

OCH CH Br 2

BrCH„CH„Br

2

+

K ~0C(CH,J,

10% KOH, Y-73% OH

+

Ph P+CH=CHP Ph Et ψ. CHC1 ή 3

H C=CH0Ac o

2» "2""4 -22°,Y=30%

0 ^

OH

toe ©

HCS£CH, NaOH/H 0 2

200°, lOOOpsi

ÔXOJ

Y=80% SCHEME VI

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

110

The extended chain a c r y l a t e 13 has not been r e p o r t e d . No r e p o r t s e x i s t concerning b i o l o g i c a l a c t i v i t y of monomers 14, 16, or 28, derived from t r i b r o m o s a l i c y l a n i l i d e , or 17, 19, or 30 d e r i v e d from o-benzyl-p-ehlorophenol. 2

PolymerizationsI ,14,16 F u n g i c i d a l a c r y l a t e s 8, 11, 14, and 17 were homopolymerized i n s o l u t i o n u s i n g r a d i c a l i n i t i a t i o n (AIBN).14 Only very low y i e l d s and low molecular weights were obtained with 17, presum­ ably due to the high c h a i n t r a n s f e r constant expected from the d i b e n z y l i c methylene f u n c t i o n w i t h i n t h i s monomer.14 A n i o n i c i n i t i a t i o n of 17 with LiAlIfy i n THF a l s o f a i l e d . A 24% y i e l d of a low molecular weight homopolymer of 17 r e s u l t e d from thermal p o l y m e r i z a t i o n at 150°C. Good y i e l d s and high molecular weights could be achieved i n th Chain-extended a c r y l a t e m e r i z a t i o n under AIBN i n i t i a t i o n . Sample homopolymerization r e s u l t s are summarized i n Table 1.14 A c r y l a t e s 8, 14, and 17 were a l s o copolymerized with nhexyl methacrylate o r η-butyl a c r y l a t e i n emulsion r e a c t i o n s (sodium l a u r y l s u l f a t e , K2S2OQ, 60°C) as were chain-extended a c r y l a t e s 10, 13, 16 and 19.14 The copolymers of 17 and 19 were low molecular weight m a t e r i a l s again due to easy c h a i n t r a n s f e r . The bulk copolymerization of 19 with n-hexyl methac­ r y l a t e gave reasonably high molecular weights.14 Some s o l u t i o n copolymerizations were a l s o c a r r i e d out. Representative r e s u l t s are summarized i n Table 2. A s e r i e s o f f i l m forming v i n y l acetate or e t h y l a c r y l a t e copolymers were prepared where the f u n g i c i d a l monomers was pentachlorophenyl a c r y l a t e , 8, 8 - q u i n o l y l a c r y l a t e , 11, or a c r y l y l s a l i c y l a n i l i d e , 20.I In these copolymers the mole f r a c t i o n o f the f u n g i c i d a l monomer was kept low ( i . e . between 0.04 and 0.11). Representative copolymers are summarized i n Table 3 . I These co­ polymers were prepared by bulk copolymerization using the f r e e r a d i c a l i n i t i a t o r s AIBN (with 8) and t - b u t y l p e r o x y p i v a l a t e (BPP) (with 11 and 20). The copolymer compositions were determined both by elemental analyses and p y r o l y s i s gas chromatography.12 As expected with bulk p o l y m e r i z a t i o n s , broad molecular weight d i s t r i b u t i o n s were obtained. As can be seen i n Table 3, the molecular weights were high. The g l a s s t r a n s i t i o n temperatures increased as the mole content of the f u n g i c i d a l monomer increased (Table 3 ) . I The s e n s i t i v i t y o f Tg to small i n c o r p o r a t i o n s of 8, 11, o r 20 i n d i c a t e s the homopolymers of these monomers would have high Tg v a l u e s . Bulk copolymerizations o f 2 - ( 4 - t h i a z o y l ) b e n z i m i d a z o l e a c r y l a t e , 21, with e t h y l a c r y l a t e were s u c c e s s f u l . ! However, attempts to copolymerize 21 with v i n y l a c e t a t e i n bulk gave only 2

2

2

f

2

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

8. PITTMAN AND STAHL

Fungicides for Paints

111

Table 1-Representative Homopolymerization Reactions

Fungicidal Monomer

Solvent

8 14 17 17 17 10 13 19 25 28 32

Benzene Benzene Benzene THF neat Benzene Benzene Ethylbenzene Benzene Benzene neat

(a)

MJJ =

80,000.

_

(b)

M

24,000,

M

N

=

W

=

Initiator AIBN AIBN AIBN LiAlH AIBN AIBN AIBN AIBN AIBN AIBN

4

Conditions °C/time, hr

Yield (%)

60/36 70/24 60/20 -78-*20/14 150/8 65/51 58/72 68/14 70/24 68/24 70/25

87 75b 0 0 24 0 0 0 0 0 0

50,000.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

a

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

(b)

(a)

n-HM n-HM n-HM n-HM n-BA MMA and n-BA n-HM n-HM n-BMA MMA n-BA n-BA

a

22 7.9 27.6 9.5 9.5 4.3 11.1 6.6 30 1.1 23 31 2

2

2

2

2

2

2

2

2

2

2

2

2

K S 0 K2S 0 K S 0 K S 0 K S 0 AIBN K S 0 AIBN AIBN K S 0 AIBN AIBN 7

8

8

8

8

8

8

b

b

b

b

b

SLS SLS SLSb SLS SLS Bz s o i n . SLS Bulk Bz/soln. SLS Bz/soln. Bz/soln.

b

l In Feed mole % I n i t i a t o r System

M

o f F u n g i c i d a l Monomers

52/5 48/41 70/24 72/22 70/18 74/23 65/20 70/20 63/28 61/20 66/24 66/26

98 34 51 79 68 48 10 49 19 90 0 0 15.6 3.2 33 9.3 4.8 3.2 9.7 2.7 1.5 0 0 0

-

1.3 0.9 0.21 1.53 13.3 5.1 0.2 0.87 0.24 5.8

Conditions Mole % Temp. Fungicidal °C/Time, Y i e l d Monomer i n I * i T H F hr Polymer (dl/g) (%)

Copolymerizations

4

M

W

-

-

13.6 8.4 17

-

17

-3.6 40 7.3 *0.5 6.3 3.1 9.3

50

8.6

-1.9 -9.3

xio- xi o-5

n-HM = hexyl methacrylate, n-BA = η-butyl a c r y l a t e , n-BMA = η-butyl methacrylate, and MMA = methyl methacrylate. Emulsion polymerizations using sodium l a u r y l s u l f a t e as the s u r f a c e a c t i v e agent.

8 14 17 10 13 16 19 19 25 28 30 32

Fungicidal Monomer Μχ Comonomer

Table 2-Representative

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EA EA EA VA VA VA EA EA EA VA VA VA EA EA EA VA VA VA

8 8 8 8 8 8 11 11 11 11 11 11 20 20 20 20 20 20

2

M

jicidal lomer Μχ

b

131 283 2,860 61 329 3,320 40 200 2,000 47 233 2,330 34 267 2,670 62 311 3,107

2

Μ /Μχ 70 70 60 70 70 70 50 60 60 60 60 50 60 50 50 50 60 60

Temp. °C 2.5 2.5 2 3 3 4 3 2.5 2.5 3 3 2.5 1.5 2.0 2.5 3.0 3.5 2.0

Time hr 58 57 58 60 59 60 69 59 65 58 53 56 49 70 71 95 71 73

Conv. % 0.80 0.57 0.06 5.46 1.12 0.06 1.90 1.25 0.60 11.5 2.5 0.5 1.75 0.61 0.48 1.52 0.61 0.36

Mole % Ml i n Copolymer

c

N

Me

6.6 6.8 7.4 8.9 7.5 7.7 9.3 14.0 15.0 6.5 5.1 9.8 8.6 9.4 9.3 6.4 6.8 7.1

X10"

4

2.4 1.7 1.2 1.2 1.2 1.1 3.1 3.1 3.4 3.2 2.2 2.1 3.3 3.2 3.0 3.2 3.0 2.7

V , X10~ 5

f

-4 -6 -18 38 35 32 1 -3 -7 43 37 34 -7 -11 -12 37 32 30

xg °c

Table 3 — c o n t i n u e d on next page

0.95 0.60 0.10 5.50 1.15 0.2 2.25 1.35 0.65 12.3 2.4 0.5 1.85 0.70 0.65 1.75 0.75 0.45

Mole % Ml i n Copolymer

d

a

Table 3-Sample Bulk Copolymerizations o f F u n g i c i d a l A c r y l a t e s 8, 11, and 20 with E t h y l A c r y l a t e o r V i n y l A c e t a t e

5i

g:

f

32 r

D

> •z >

1

00

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

(d) (e) (f)

(b) (c)

(a)

Table

A z o b i s i s o b u t y r o n i t r i l e was the i n i t i a t o r i n copolymerizations of 8 w h i l e t - b u t y l p e r o x y p i v a l a t e was employed i n compolymerizations of 11 or 20. EA = E t h y l a c r y l a t e , VA = V i n y l a c e t a t e . Determined by c h l o r i n e a n a l y s i s ( i n copolymerizations of 8) or n i t r o g e n a n a l y s i s ( i n copolymerizations of 11 or 20). C a l c u l a t e d from p y r o l y s i s gas chromatography determinations. Determined by GPC. Evaluated from d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC) where Tg f o r p o l y ( e t h y l a c r y l a t e ) = -24°C and p o l y v i n y l acetate) = 28°C.

3—continued

8.

PITTMAN A N D STAHL

115

Fungicides for Paints

low molecular weight, o i l y p r o d u c t s . I These c o p o l y m e r i z a t i o n s are summarized i n Table 4 where one can see the value of Tg i n c r e a s e s as the molar content of 21 i n c r e a s e s . 2

In order to determine the r e a c t i v i t y of pentachlorophenyl a c r y l a t e , 8, i n r a d i c a l i n i t i a t e d c o p o l y m e r i z a t i o n s , i t s r e l a t i v e r e a c t i v i t y r a t i o s were obtained w i t h v i n y l acetate ( M ) , τ χ = 1 . 4 4 and r =0.04 u s i n g 31 c o p o l y m e r i z a t i o n experiments, and w i t h e t h y l a c r y l a t e ( M ) , r]=0.21 and r =0.88 u s i n g 20 experiments.13 The composition conversion data was c o m p u t e r - f i t t e d to the i n t e g r a t e d form of the copolymer equation u s i n g the n o n l i n e a r l e a s t - s q u a r e s method of T i d w e l l and M o r t i m e r , ^ ! which had been adapted to a computerized format e a r l i e r . 2

2

2

2

4 2

In t h i s work,13 g l a s s t r a n s i t i o n temperatures were s t u d i e d as a f u n c t i o n of copolyme a c r y l a t e ) e x h i b i t e d th i z e s these Tg values versus Μχ/Μ content of both v i n y l acetate and e t h y l a c r y l a t e copolymers.13 χ xg values f o r copolymers w i t h higher mole f r a c t i o n s of 8 depended on t h e i r thermal h i s ­ t o r y . Tg i n c r e a s e s a f t e r h e a t i n g above Tg the f i r s t time. For example a v i n y l a c e t a t e copolymer (mole f r a c t i o n of 8 = 0.67) e x h i b i t e d Tg values of 7 7 ° , 9 9 ° , and 103°C i n three s u c c e s s i v e heating cycles.13 2

η β

Since a l l the f u n g i c i d a l monomers give homopolymers w i t h a high g l a s s t r a n s i t i o n temperature, Tg, p a i n t binder polymers con­ t a i n i n g the f u n g i c i d e s must be designed to have lower Tg v a l u e s . Therefore, a terpolymer a c r y l i c binder design c o n s i s t i n g of (1) the f u n g i c i d a l a c r y l a t e , (2) methyl m e t h a c r y l a t e , and (3) a low Tg a c r y l a t e such as η - b u t y l a c r y l a t e or 2 - e t h y l h e x y l a c r y l a t e was s e l e c t e d . S e v e r a l terpolymer samples were made i n s o l u t i o n i n small amounts. For example, s o l u t i o n t e r p o l y m e r i z a t i o n of 16 w i t h methyl methacrylate and η - b u t y l a c r y l a t e gave a good terpolymer, as d e s c r i b e d i n Table 2. I t i s of i n t e r e s t that extended-chain a c r y l a t e s , w h i l e r e s i s t i n g A I B N - i n i t i a t e d homop o l y m e r i z a t i o n , underwent t e r p o l y m e r i z a t i o n . This important o b s e r v a t i o n c l e a r e d the way f o r the s y n t h e s i s of s t a b l e t e r p o l y ­ mer l a t i c e s c o n t a i n i n g these slower h y d r o l y z i n g monomers. Latex formulations were needed f o r f u r t h e r mixing i n t o sample p a i n t s for testing. F u n g i c i d a l v i n y l ethers 25 » 30 and 32 » r e s i s t e d r a d i c a l i n i t i a t e d homopolymerization. Copolymerizations of these mono­ mers w i t h η - b u t y l a c r y l a t e or methyl methacrylate were g e n e r a l l y u n s a t i s f a c t o r y . At low mole r a t i o s of f u n g i c i d a l v i n y l ether to a c r y l a t e , copolymers could be i s o l a t e d w i t h e i t h e r very low or no i n c o r p o r a t i o n of the v i n y l e t h e r s .

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

M

(b) (c)

(a)

23 49 98 248 498

l/M

2

% 48 48 53 60 63

24 24 24 24 8

Conv.

Time hr 6.4 4.4 2.5 2.4 1.9

χ

b

Mole % Μ in Copolymer

2

0.7 1.3 1.6 2.5 2.2

X10"

a

5

was

XI0""

In each run AIBN (0.04g) was used as i n i t i a t o r and 18 to 20g of e t h y l a c r y l a t e employed. C a l c u l a t e d from n i t r o g e n analyses. C a l c u l a t e d from GPC.

60 60 55 60 58

Temp. °C

f

Table 4-Sample Bulk Copolymerizations of 2 - ( 4 - T h i a z o y l ) b e n z i m i d a z o l e A c r y l a t e , 21, With E t h y l A c r y l a t e ( M )

°c

Tg

H on

m ζ

I

m τι m ο Η ζ/3 Ο τι Χ Ο Η r m m •ζ


3

Table 6-Composition of Stable L a t i c e s of Model P a i n t Binders Containing Chemically Bound F u n g i c i d e s

120

EFFECTS OF HOSTILE ENVIRONMENTS

rs. ΝΟ co

co r»s m oo oo co ON Ή «H RH 1—1

o O O ON Γ"- o ON

s

ο

«*•

g

a

Ο

δ-

ο

8

Qi

>

f

DO

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Spiked Indolene

Indolene

Spiked Indolene

Indolene

Gasoline 0 5 10 15 25 50 75 100 0 5 10 15 25 50 75 0 5 10 15 25 50 75 100 0 5 10 15 25 50 75

% MTBE 12.9 10.1 10.4 10.0 10.0 10.5 10.2 10.0 9.1 9.9 10.0 10.1 10.0 10.0 9.7 9.3 14.9 8.0 7.9 8.0 7.9 7.6 7.5 7.8 7.7 6.4 6.6 6.5 6.6 6.5 7.1 6.7

Durometer Shore A Points 89 75 74 74 72 72 73 68 66 70 67 68 67 69 67 66 70 56 56 57 57 60 57 58 59 56 53 52 53 54 55 55

Modulus at 100% Elongation MPA 9.1 8.6 8.5 8.6 8.6 8.5 8.7 8.5 8.6 8.5 8.5 8.6 8.4 8.5 8.3 8.4 4.5 3.5 3.8 3.8 4.0 3.9 4.1 4.2 4.5 4.7 4.3 4.6 4.2 4.3 4.3 4.0

Elongation % 180 140 140 125 135 135 113 118 103 117 118 120 121 116 118 109 350 222 210 208 198 195 180 185 170 135 152 142 153 150 157 152

V—Continued

* Formulation No. 21889-33-1 which is different from the one used for the ethanol/gasoline investigation.

Butadiene-Aerylon i t r i l e (Nitrile)

Eplchlorohydrin* Homopolymer

Elastomer

Table Tensile Strength MPa

2 2 2 3 3 3 4 3 3 3 3 3 4 4

-2

-

33 33 34 35 37 40 44 46 53 68 67 66 66 65 65

3 4 4 4 6 6 7 5 6 6 6 6 6 6

-3

Extractables %

14 16 17 17 19 22 31 44 23 24 25 26 27 32 39

-

Volume Change %

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Ethylene-PropyleneDiene Terpolymer

Chlorosulfonated Polyethylene

Elastomer

Spiked Indolene

Indolene

Spiked Indolene

Indolene

Gasoline 0 5 10 15 25 50 75 100 0 5 10 15 25 50 75 0 5 10 15 25 50 75 100 0 5 10 15 25 50 75

% MTBE 17.3 13.4 16.0 17.9 21.7 18.4 19.0 20.3 18.9 18.8 16.5 17.4 14.1 18.1 18.8 15.4 9.1 4.1 3.5 3.9 4.0 4.1 4.0 4.4 5.0 3.7 4.0 4.4 4.2 4.3 4.0 4.2

Tensile Strength MPa 222 97 100 122 120 100 103 103 97 88 78 75 63 73 88 97 217 80 72 78 83 87 83 100 112 77 82 88 85 90 90 100

87 66 67 68 58 63 58 65 68 69 58 70 61 67 67 58 67 39 37 42 40 41 43 47 43 41 43 39 40 42 43 41 4.2

_-

4.3

3.6 4.4

-

13.0 16.0 17.2 18.8 18.4 17.2 20.1

Durometer Shore A Points

Modulus at 100% Elongation MPA

V—Continued

Elongation %

Table

-

138 131 139 132 128 108 99 79 143 141 139 136 133 116 103

-

45 47 48 46 48 53 55 57 74 71 68 70 67 70 60

Volume Change %

-

18 18 18 18 18 18 18 19 18 18 18 18 19 18 18

2 1

1 ι 1 1 ι ι 1 1 1 1 1

-0

Extractables %

242

EFFECTS OF HOSTILE ENVIRONMENTS

% MTBE in Indolene HO III Figure 4. Volume change of elastomers as a function of MTBE concentration in Indolene HO-III. Key: o,fluorocarhon; •, epichlorohydrin homopolymer: A, chlorosulfonated polyethylene: and o, EPDM.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

14.

ABU-ISA

Effects of Gasoline Blends on Elastomers

243

as e p i c h l o r o h y d r i n homopolymer e x h i b i t moderate increases i n volume s w e l l with increased MTBE c o n c e n t r a t i o n s . Some other elastomers e x h i b i t only s l i g h t increases i n s w e l l , f o r example, c h l o r o s u l f o n a t e d polyethylene; s t i l l others e x h i b i t a continuous decrease i n s w e l l with increased MTBE c o n c e n t r a t i o n , f o r example, EPDM. Q u a l i t a t i v e l y MTBE i s estimated to have an o v e r a l l s o l u b i l i t y parameter value c l o s e to that of Indolene, but has higher p o l a r and hydrogen bonding f o r c e s . As a r e s u l t polar polymers such as f l u o r o c a r b o n , e p i c h l o r o h y d r i n homopolymer and c h l o r o s u l f o n a t e d polyethylene tend to s w e l l to a g r e a t e r extent i n MTBE r i c h mix­ t u r e s , while nonpolar EPDM elastomer swells to a l e s s e r extent i n these mixtures. The very l a r g e s w e l l of the f l u o r o c a r b o n i n MTBE i s not s u r p r i s i n g s i n c e other ethers such as d i e t h y l ether and dioxane are known to s w e l l the f l u o r o c a r b o n to a l a r g e extent [ 3 ] . As i n the case of elastomers i n MTBE mixture and e l o n g a t i o n as shown i n Table V. A d d i t i o n of toluene to Indo­ lene HO-III to make "spiked" Indolene leads to increased s w e l l of elastomers i n t h i s f u e l and i t s mixtures (Tables V and V I ) . In the case of a l l the s i x polymers i n v e s t i g a t e d i n c r e a s i n g the aromatic content from 30 to 50% has a more d e t r i m e n t a l e f f e c t on elastomers than the a d d i t i o n of 10% MTBE (Table V I ) . Comparison of the E f f e c t s of Methanol, Ethanol and MTBE Mixtures on Elastomers. The s w e l l behaviors of elastomers i n methanol/ Indolene mixtures have been adequately explained i n terms of the s o l u b i l i t y parameter concept [ 2 ] . I t was found that with the exception of the f l u o r o c a r b o n elastomer the o v e r a l l s o l u b i l i t y parameter of elastomers was equal to that of the methanol/lndolene mixture i n which maximum s w e l l of the elastomer was measured. Ethanol has an o v e r a l l s o l u b i l i t y parameter [4] of 13.0 ( c a l / c c ) ^ . The c o n t r i b u t i o n s of the London d i s p e r s i o n (nonp o l a r ) f o r c e s , polar forces and hydrogen bonding f o r c e s to the o v e r a l l s o l u b i l i t y parameter are 6^=7.5, δ =4.3 and 0^-10.9 ( c a l / c c ) ' r e s p e c t i v e l y . The o v e r a l l s o l u b i l i t y parameter o f ethanol i s s l i g h t l y lower i n value than the s o l u b i l i t y parameter of methanol mainly due to smaller c o n t r i b u t i o n s by the p o l a r f o r c e s . The δ f o r ethanol i s 4.3 as compared to 6.0 ( c a l / c c ) ' for methanol. The s w e l l behavior of most elastomers In ethanol resembles that i n methanol. In order to examine whether or not the s w e l l data In ethanol obtained f o r the v a r i o u s polymers (Table I I I ) can be explained i n terms of the s o l u b i l i t y parameter concept we compared e s t a b l i s h e d s o l u b i l i t y parameters of the e l a s ­ tomers with those c a l c u l a t e d from maximum s w e l l data. The s o l u ­ b i l i t y parameters of nine of the elastomers i n v e s t i g a t e d have been reported i n the l i t e r a t u r e [3-6] and are shown i n column 2 of Table V I I . The next column of the Table i s generated from the present data and l i s t s the concentrations of ethanol i n the 2

ρ

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

Elastomer

14

46

57

79

Butadlene-Acrylonltrile

Chlorosulfonated Polyethylene

Ethylene-PropyleneDiene Terpolymer

138

45

33

11

21

44

Polyester lire thane

1

122

MTBE

Epichlorohydrin Homopolymer

Fluorocarbon

143

74

53

23

23

3

67

138

138

68

34 48

24

23

5

17

13

2

Volume Swell (%) After 72 Hr. Immersionι in Mixtures of 10% MTBE in Spiked Spiked Indolene Indolene Indolene Indolene

9.1

17.3

14.9

12.9

23.0

18.3

Original Tensile Strength MPa

5.0

18.9

7.7

9.1

17.7

4.5

4.1

13.4

8.0

10.1

18.3

14.3

3.7

18.8

6.4

9.9

15.2

15.1

3.9

17.9

8.0

10.0

17.3

14.8

4.4

17.4

6.5

10.1

15.7

15.2

Tensile Strength (MPa) After 72 Hr Immersion in Mixtures of 10% MTBE in Spiked Spiked MTBE Indolene Indolene Indolene Indolene

Volume Swell and Tensile Strength of Elastomers After Exposure to Methyl t-Butyl Ether (MTBE), Indolene HO-III, Spiked Indolene HO-III, and 10% MTBE mixtures with Each of the Indolenee

m

ι


Ρ00· ^POOH + P-

(33) (34)

Oxygen r e a c t s f a s t w i t h a l l types o f a l k y l and a l l y l polymer r a d i c a l s formed. The o x i d a t i o n may cause the polymeric m a t e r i a l s to c r o s s l i n k which causes hardening or shrinkage and may show up as s t r e s s c r a c k i n g . The a u t o x i d a t i o n may degrade the macromolec u l e s to lower molecular weight and v o l a t i l e products, causing volume decrease o r s t r e s s c r a c k i n g o f the polymer. I t may a l s o lead to a c i d i c products which w i l l d i s c o l o u r the m a t e r i a l or b r i n g about f u r t h e r degradations.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

302

O x i d a t i o n processes with atomic oxygen, ozone and s i n g l e t oxygen The photochemical smog contains s e v e r a l oxygen s o e c i e s such as atomic oxygen (0), ozone (0^) and s i n g l e t oxygen ( 0^) which are h i g h l y r e a c t i v e with s e v e r a l polymers. The c o n c e n t r a t i o n o f 0 and 0j i s low and t h e i r e f f e c t i s considered to be l e s s important i n the t o t a l c o r r o s i o n o f polymers than the e f f e c t s o f ozone, n i t r i c and s u l f u r i c a c i d s . Atomic oxygen (0) r e a c t s r a p i d l y with s e v e r a l polymers (PH) by a b s t r a c t i o n o f hydrogen and formation o f polymer o x y r a d i c a l s (P0-) ' ' PH + 0 p. + o

** P- + -OH 2

(35)

— * P0£

(36)

H i g h l y branched polymer with other l i n k s , e.g. poly(oxymethylene), are most r e a d i l y attacked by atomic oxygen. P e r f l u o r i n a t e d polymers, rubber v u l c a n i z e d with s u l f u r , and h i g h l y aromatic polymers are the most r e s i s t a n t . Ozone (O3) p l a y s a s i g n i f i c a n t r o l e i n o x i d a t i o n and degrad a t i o n o f s e v e r a l p^|ym|r^s^çh^gs: p o l y o l e f i n s , rubber, p o l y s t y rene and polyamides . Ozone may a b s t r a c t hydrogen and form polymer p e r o x y r a d i c a l s (POO*): 9

PH + 0

9

9

1» POO* + -OH

3

(37)

or add to double bonds with formation o f ozonides, which are uns t a b l e and e a s i l y decomposed i n t o aldehydes and a c i d s : 0

-CH=CH- + 0

/ 0

\ 0

I

I

0

\

* - C - C-

o

H

-C

H r

e

a

HO

I +

H c

t

C-

(38)

0

s

S i n g l e t oxygen (^ί^) mainly with unsaturated polymers by "enetype" r e a c t i o n s with |^rm|t|gn o f hydroperoxy groups and s h i f t i n g o f the double bond ' : 9

UUH. l

-CH -CH=CH- + 0 2

2

*

-CH=CH-CH-

(39)

As a r e s u l t o f these o x i d a t i o n r e a c t i o n s polymeric m a t e r i a l s g r a d u a l l y lose t h e i r u s e f u l mechanical p r o p e r t i e s . During the o x i d a t i o n degradation (mainly by b e t a - s c i s s i o n processes) and c r o s s l i n k i n g r e a c t i o n s occur.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

17.

RÂNBY AND RABEK

Non-oxidative

Environmental Corrosion

303

processes

In p o l l u t e d a i r other degradative r e a c t i o n s i n the absence of oxygen may a l s o occur. The presence o f water, e s p e c i a l l y a c i d i c water, may b r i n g about h y d r o l y t i c r e a c t i o n s and, i f oxygen a l s o i s present, may increase the o x i d a t i o n r e a c t i o n s . A l l these r e a c t i o n s may be going on simultaneously and i n the most complicated manner. The r e s u l t i n g lower molecular weight u n i t s can cause changes i n flow, shape, strength and other mechanical p r o p e r t i e s . P h y s i c a l changes may r e s u l t from d i s t o r t i o n o f the polymeric m a t e r i a l by s u n l i g h t due to photodegradation and p h o t o c r o s s l i n k i n g and can be p h o t o s e n s i t i z e d by the presence o f i m p u r i t i e s on the surface which e f f i c i e n t l y absorb l i g h t . Energy t r a n s f e r processes may p l a y a considerable r o l e . D i f f u s i o n and m i g r a t i o n o f a d d i t i v e s from the polymer matrix i n t o a surface may have The s i d e e f f e c t may be a p l a s t i c i z e r s or from the l o s s o f other low molecular a d d i t i v e s or even water, which can act as p l a s t i c i z e r s . D i f f e r e n t i a l expansion of organic and i n o r g a n i c a d d i t i v e s can r e s u l t i n c r a c k i n g o f the polymeric m a t e r i a l s . These r e a c t i o n s may add to the r e a c t i o n s caused by p o l l u t e d atmosphere. They are p a r t i c u l a r l y p o s s i b l e a t temperatures near those where changes or property t r a n s i t i o n s occur ( f o r example at s o f t e n i n g and m e l t i n g p o i n t s o r b r i t t l e p o i n t s o f the m a t e r i a l s ) . S e r v i c e L i f e o f Polymeric

M a t e r i a l s i n P o l l u t e d Atmosphere

The d e t e r i o r a t i o n o f p l a s t i c s and other polymeric ma^egj.a^ i n p o l l u t e d atmosphere takes place i n a number o f stages ' : 1. 2. 3. 4. 5. 6.

Loss o f g l o s s Minute c r a z i n g Severe c r a z i n g and c r a c k i n g Leaching Loss of reinforcement from the s t r u c t u r e Gradual breakup

The timescale f o r these processes to occur i s dependent on the type of polymer, the content of added m a t e r i a l s , p l a s t i c i z e r s and a d d i t i v e s such as a n t i o x i d a n t s , p h o t o s t a b i l i z e r s , thermostab i l i z e r s , e t c ) , f i l l i n g and r e i n f o r c i n g m a t e r i a l s such as p a r t i c les and f i b e r s , e t c . The f i r s t observed e f f e c t i s the l o s s o f surface g l o s s which i s an obvious s i g n o f d e t e r i o r a t i o n o f a polymeric m a t e r i a l . The gloss can be l o s t by a b r a s i o n from p a r t i c u l a t e matter (sometimes i n r a i n ) , surface l e a c h i n g and minute and severe c r a z i n g . A f t e r extended exposure times the polymeric m a t e r i a l s may l o s e t h e i r mechanical p r o p e r t i e s f o r p r a c t i c a l use.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

304

D i s c o l o r a t i o n of polymeric m a t e r i a l s i s u s u a l l y the r e s u l t of complicated photochemical r e a c t i o n s and the e f | e c t of surface r e a c t i o n with S0 , N0 , * s i n g l e t oxygen ( 0 >. The s e r v i c e l i f e of p l a s t i c s and other polymeric m a t e r i a l s i s a p a r t i c u l a r problem i n Los Angeles and Tokyo because of the spe­ c i a l c l i m a t i c c o n d i t i o n s f o r formation of photochemical smog. T h i s s i t u a t i o n i s by no means confined to the USA and Japan. Photoche­ m i c a l smog and environmental c o r r o s i o n of polymers i s commonly observed i n some European c i t i e s , notably Madrid, Athens and London. In Stockholm where a i r p o l l u t i o n i s at a low l e v e l these problems are p r e s e n t l y not seen so s e r i o u s . 3 η α

2

2

2

Conclusions The c o n c e n t r a t i o n of a i r p o l l u t a n t s i s very important f o r the longterm p r o p e r t i e s that the problem of environmenta g i b l e i n comparison with the p h y s i c a l , t h e r m a l and photochemical ageing of polymers. The t a b l e s I-IV show that annual emission of p o l l u t a n t s i n t o the atmosphere i s tremendous, and the e f f e c t s on polymers of i n d i v i d u a l p o l l u t a n t s ( p a r t i c l e s , s u l f u r oxides, n i t r o g e n oxides, hydrocarbons, oxygen compounds, a c i d r a i n , etc) should be taken i n t o s e r i o u s c o n s i d e r a t i o n and be the subject of more d e t a i l e d research. The cost of environmental c o r r o s i o n must i n c l u d e the d e t e r i o r a t i o n of such d i v e r s e o b j e c t s as polymeric b u i l d i n g m a t e r i a l s , outdoor e l e c t r i c a l l i n e s with polymeric i n ­ s u l a t i o n , rubber t i r e s , painted s u r f a c e s , e t c . The c o s t can only be estimated and no d e f i n i t e f i g u r e s are a v a i l a b l e . A d d i t i o n a l costs i n c l u d e the work f o r replacement and s u b s t i t u t i o n of corroded polymeric m a t e r i a l s , e.g. i n machinery and b u i l d i n g c o n s t r u c t i o n s . Observations of polymeric m a t e r i a l s , e.g. house p a i n t , used i n heavy p o l l u t e d a r e a s demonstrate that the e f f e c t s of environmental c o r r o s i o n are c l e a r l y v i s i b l e . T h i s paper does not cover a l l aspects of t h i s subject. The references c i t e d here are s e l e c t e d from hundreds of p u b l i s h e d r e p o r t s , and they are given as examples to i l l u s t r a t e the impor­ tance of the problem. The need f o r more research i s amply v e r i ­ f i e d , both on the e f f e c t s and t h e i r prevention. Since 1971 our department i s i n v o l v e d i n study of photodegradat i o n , s e n s i t i z e d photooxidation and p h o t o s t a b i l i z a t i o n of polymers. A b i g e f f o r t i s made i n the study of s i n g l e t oxygen o x i d a t i o n of s e v e r a l important polymers, such as polydienes, p o l y ( v i n y l c h l o ­ r i d e ) , p o l y s t y r e n e and p o l y e s t e r s , r e a c t i o n s of atomic oxygen and ozone with polydienes and p h o t o s t a b i l i z a t i o n of these polymers. As a r e s u l t of t h i s work, a USA-Swedish Workshop on "Photodegrad a t i o n and P h o t o g g a b i l i z a t i o n of Polymers" was organized i n Stockholm i n 1981 . At t h i s meeting s e v e r a l problems i n c l u d e d i n t h i s paper were d i s c u s s e d . The workshop concluded that a broad i n t e r n a t i o n a l cooperation should be explored and current research on t h i s problem expanded.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

17.

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Environmental Corrosion

305

Areas r e q u i r i n g s p e c i a l a t t e n t i o n i n the f u t u r e i n c l u d e improved s t a b i l i z a t i o n processes f o r e x i s t i n g polymers and the synthesis of new polymeric m a t e r i a l s which are more r e s i s t a n t against environmental c o r r o s i o n than those p r e s e n t l y used. The i m p l i c a t i o n s of the s t a b i l i t y o f n a t u r a l polymers f o r the p r e d i c t i o n o f s e r v i c e l i f e o f s y n t h e t i c polymers,the general e f f e c t s o f h y d r o l y s i s , the l i g h t - i n d u c e d h y d r o l y t i c degradation are r e l e v a n t research t o p i c s . This paper includes r e s u l t s from our research programs on photooxidation and p h o t o - s t a b i l i z a t i o n o f polymers supported by the Swedish N a t i o n a l Board f o r T e c h n i c a l Development (STU) and a p r o j e c t i n the NORDFORSK program on s i n g l e t oxygen r e a c t i o n s . Literature Cited

1. Perkins, H.C., "Air Pollution",McGraw-Hill, N.Y., 1974 2. Lynn, D.A., "Air Pollutio Wesley, Reading Pa 3. Holum, J.R., "Topics and Terms in Environmental Problems", Wiley, N.Y., 1978. 4. Faith, W.L. and Atkinsson, A.A., "Air Pollution", 2nd ed. Wiley, N.Y., 1972 5. Friedlander, S.K., "Smoke, Dust and Haze, Fundamental of Aerosol Behaviour", Wiley, N.Y., 1977. 6. Cavender, J.H., Kircher, D.S. and Hoffman, A.J., Nationalwide Air Pollutant Emission Trends 1940-1970, EPA Publication No. AP-115, 1973. 7. Rosato, D.V. and Schwartz, R.T., "Environmental Effects on Plastics Materials", Wiley-Interscience, N.Y., 1968,1-2. 8. Kinslow, R., Intern. Sci. Technol., 1965, 40, 38. 9. Dainton, F.S. and Ivin, K.J., Trans. FaradaySoc.,1950, 46, 374, 382. 10. Jellinek, H.H.G. and Kryman, F.J., J. Appl. Polym. Sci., 1969, 13, 2504. 11. Jellinek, H.H.G., J. Air. Poll. Contr. Ass., 1970, 20, 672. 12. Jellinek, H.H.G., in "Photochemistry of Macromolecules" (Ed. R.F. Reinish), NASA AMES Research Center, Calif. 1970, 85, 91. 13. Jellinek, H.H.G., J. Air. Pollut. Contr. Ass., 1970, 20, 672 14. Jellinek, H.H.G. and Pavlinec J., Photochem. Macromol. Proc. Symp. (Ed. R.F. Reinish), Plenum Press, N.Y., 1970, 91. 15. Hrdlovic, P., Pavlinec J. and Jellinek, H.H.G., J. Polym. Sci., A1, 1971, 9, 1235. 16. Jellinek, H.H.G., Text Res. J., 1973, 43, 557. 17. Sharovolskaya, L.N., Degtyareva A.A. and Shrubovich, V.A., Tezy Dokl. Resp. Konf. Vyskomol. Soedin., 3rd Ed. Naukova Dumka, Kiew, USSR, 1973, 87 18. Degtyareva, A.A., Kashan, A.A., Sharovolskaya L.N. and Shrubovich, V.A., Vyskomol. Soedin., 1975, A17, 2144. 19. Degtyareva, A.A., Sharovolskaya, L.N., Shrubovich V.A. and Kashan, A.A., Fiz. Khim. Polim., 1975, 15, 147.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

306

EFFECTS OF HOSTILE ENVIRONMENTS

20. Davidson, J.A. and Abrahamson, E.W., Photochem. Photobiol., 1972, 15, 403. 21. Meterological Data for Sweden, Publ. by Institute of Meteoro­ logy, Stockholm University, Stockholm, Sweden 1970-1980. 22. Jellinek, H.H.G. and Toyoshima, Y., J. Polym. Sci., 1967, A1, 5, 3214. 23. Jellinek, H.H.G. and Flajsman, F., J. Polym. Sci., 1969, A1, 7, 1153. 24. Jellinek, H.H.G., Flajsman, F. and Kryman, F.J., J. Appl. Polym. Sci., 1969, 13, 107. 25. Jellinek, H.H.G. and Flajsman, F., J. Polym. Sci., 1970, A1, 8, 711. 26. Jellinek, H.H.G. and P. Hrdlovic, J. Polym. Sci., 1971, A1, 9, 1219. 27. Jellinek, H.H.G. and Chaudhuri, A.K., J. Polym. Sci., 1972, A1, 10, 1773. 28. Jellinek, H.H.G., Techn 357, 101. 29. Jellinek, H.H.G., Yokota, R. andIoth,Y., Polym. J., 1973, 4, 601. 30. Jellinek, H.H.G. and Wang, T.J.Y., J. Polym. Sci., 1973, A1, 11, 3227. 31. Jellinek, H.H.G., Martin, F. and Wegener, Η., J. Appl. Polym. Sci., 1974, 18, 1778. 32. Jellinek, H.H.G. Technical Report No. 782950 US NTIS, 1974. 33. Rabek, J.F., Lucki, J. and Ranby, B., Europ. Polym. J., 1979, 15, 1089. 34. Huber, H. and Joerg, F., Staub-Reinhalt. Luft, 1979, 39, 211. 35. Kambe, C.H. and Yokota, R., Polym. Eng. Sci., 1980, 20, 696. 36. Huber, H. and Joerg, F., Staub-Reinhalt. Luft., 1981, 41, 1. 37. Estefan, R.M., Gause, E.M. and Rowlands, J.R., in "The Chem­ istry of Air Pollution", MSS Information Co., N.Y., 1973, 55. 38. Tusday, C.S., "Chemical Reactions in Urban Atmosphere", Else­ vier, N.Y., 1971. 39. "Photochemical Smog and Ozone Reactions". (Ed. R.F. Gould), ACS Ser. No. 113, Washington D.C., 1972. 40. Stephens, E.R., Calif. Air. Environmen., 1969, 1, 1. 41. Carlsson, D.J. and Wiles, D.M., J. Polym. Sci., 1973, Β 11, 759. 42. Aspler, J., Carlsson, D.J. and Wiles, Μ., Macromolecules, 1976, 9, 691. 43. Carlsson, D.J., Garton, A. and Wiles, D.M., Macromolecules, 1976, 9, 695. 44. Rabek, J.F. and Ranby, B., Rev. Roum. Chim., 1980, 25, 1045. 45. Ranby, B., and Rabek, J.F., "Photodegradation, Photooxidation and Photostabilization of Polymers", Wiley, London, 1975. 46. McKellar, J.F. and Allen, N.S., "Photochemistry of Man-Made Polymers", Applied Science Publ., 1979. 47. Hansen, R.H., in "Interface Conversion" (Eds. P. Weiss and G.D. Cheever), Elsevier, N.Y., 1968, 287.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

17.

RAN BY AND RABEK

Environmental Corrosion

307

48. Hansen, R.H., in "Thermal Stability of Polymers" (Ed. R.T. Conley), Dekker, N.Y., 1970, 153. 49. Hansen, R.H., Pascale, J.V., DeBenedictis, T. and Rentzepis, P.M., J. Polym. Sci., 1965, A1, 3, 2205. 50. Reneker, D.H. and Bolz, L.H., J. Makromol. Chem. Sci. Chem., 1976, A10, 599. 51. Razumovski, S.D., Reutova, L.M., Niazashvili, G.A., Tutorski, I.A. and Zaikov, G.E., Dokl. Akad. Nauk SSSR, 1970, 194, 1127. 52. Razumovski, S.D., Kefeli, A.A. and Zaikov, G.E., Europ. Polym. J., 1971, 7, 275. 53. Kefeli, Α.Α., Razumovski, S.D., Markin, V.S. and Zaikov, G.E., Vyskomol. Soedin., 1972, A14, 2413. 54. DeVries, K.L. and Simonson, E.R., Ozone Chem. Technol., 1975, 257. 55. Lofqvist, A.R. and Haylock, J.C., Ozone Chem. Technol., 1975, 241. 56. Yamauchi, J., Ikemoto 1977, 178, 2483. 57. Popov, Α.Α., Krisyuk, B.E. and Zaikov, G.E., Vyskomol. Soedin., 1980, 22, 1366. 58. Popov, Α.Α., Krisuk, B.E., Blikov, N.N. and Zaikov, G.E., Europ. Polym. J., 1981, 17, 169. 59. Rabek, J.F. and Ranby, Β., Photochem. Photobiol., 1978, 28, 557. 60. Golub, M.A., NASA Technical Memorandum, No 78604, 1979. 61. Jellinek, H.H.G., Kinetics Mechanisms of Polyreactions, IUPAC Int. Symposium Macromol. Chem., Plenary Lecture, 1971, 747. 62. Jellinek, H.H.G., in "Recycling and Disposal of Solid Wastes" (Ed. T.F. Yen), Ed. Ann Arbor Sci., Mich., 1974, 185. 63. Fladsman, F.,Kem.Ind., 1974, 23, 96. 64. Zaikov, G.E., Khim. Zhizn., 1980, 20. 65. Seymour, R.B., "Plastics vs. Corrosives", Wiley, N.Y., 1982. 66. Ranby, B. and Vogl, O., Polymer News, August, 1982, 188. RECEIVED April 11, 1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

18 Influence of Sulfur Dioxide on Organic Coatings W. FUNKE and H. HAAGEN Institut für Technische Chemie, Universität Stuttgart und Forschungsinstitut für Pigmente und Lacke, E.V., Stuttgart, Federal Republic of Germany

As far as organic coatings are concerned SO is one of the most importan environment. SO y y faces to form sulfates, either before or after the coating is applied. In case of steel such sulfates stimulate atmospheric corrosion. Reactions are also possible with vehicles and pigments, giving rise to degradation and discoloration. Such reactions are sometimes assisted by oxygen and sunlight. Special emphasize will be given to the permeability of organic coatings to SO . Though literature and data are still scanty, experimental evidence exists that S0-permeability is quite remarkable. Problems and methods to neutralize or capture permeating SO in organic coatings by special film components will be discussed. 2

2

2

The i n c r e a s i n g emission o f SO2 i n t o the atmosphere (Table I) r a i s e s many s e r i o u s problems, one o f which i s the i n f l u e n c e of t h i s p o l l u t a n t on organic coatings and on t h e i r p r o t e c t i v e function!*"^ There a r e v a r i o u s important aspects o f t h i s problem which s h a l l be subsequently reviewed and d i s c u s s e d . Corrosion P r o t e c t i o n It i s w e l l known that SO^ anions s t i m u l a t e c o r r o s i o n o f s t e e l surfaces by preventing an i n s i t u formation of i r o n oxides, which may impede the d i f f u s i o n processes i n v o l v e d i n the c o r r o s i o n r e a c t i o n s ^ . These s u l f a t e anions a r e e i t h e r formed i n the a t mosphere by o x i d a t i o n o f S 0 o r by d i r e c t r e a c t i o n w i t h the s t e e l surface i n the presence o f water to form s o - c a l l e d s u l f a t e nests^. The l a t t e r transformation may take p l a c e a t the unprot e c t e d metal surface o r p o s s i b l y , at l e a s t i n p r i n c i p a l , a f t e r SO2 has permeated the organic f i l m and a r r i v e d at the metal supp o r t . The d i f f u s i o n of SO^ anions through organic coatings seems Z

0097-6156/ 83/0229-0309S06.00/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

EFFECTS OF HOSTILE ENVIRONMENTS

310

Table I . C h a r a c t e r i s t i c SO2 Concentration L e v e l s Condition

ppm (v/v)

Emission Value Longtime Exp. (TA L u f t ) Emission Value Short Time Exp. (TA L u f t ) MEK-Value, Exp. Time 30 min. 24 h r s . 1 P e r c e p t i o n o f Smell MAC-Value Smog Alarm M o r t a l Danger K e s t e r n i c h Test 0.2 1 SO /300 1 2.0 1 SO /300 1 2

2

0.05 0.15 0.37 0.11 0.04 0. 2. 0.8 400 c a . 600 c a . 6000

Large Towns ( 2x10° inhab.) max. v a l u e Medium Towns (0.5-2x10° inhab.) Smaller Towns ( 0.5x10° inhab.) Rural S t a t i o n Urban S t a t i o n —

Industrial Station I n d u s t r i a l Area (Ruhr, West Germ.) S0 -conc. S t u t t g a r t Summer Winter

mg/m 3

0.15 0.33 0.05 0.04 0.00010.0075 0.00750.015 0.03

0.134

1

0.4 1.0 0.3 0.1

1 1 1 1

2.14 1068 c a . 1600 c a . 16000

—

Lit,

1 1 2 2

0.4 0.9 0.14 0.13 0.0010.02 0.020.04 0.08

3 4 3 3 5 5 5

max. 1.28

max. 3.4

4

max. 0.015 max. 0.05

max. 0.04 max. 0.14

1 1

2

1 ppm=l cnrvm3=2.67 mg/nP MEK=Maximal Emission Concentration MAC=Maximal Allowable Concentration - Threshold L i m i t

Value

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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311

Influence of Sulfur Dioxide

not to p l a y an important r o l e . Though l i t t l e i n f o r m a t i o n i s a v a i l a b l e on SO^ p e r m e a b i l i t y , i t may be assumed t h a t i t i s lower than that o f C l ~ . 8

SO9

Permeability

A l i t e r a t u r e search r e v e a l s d i s a p p o i n t i n g l y l i t t l e i n f o r m a t i o n on SO2 p e r m e a b i l i t i e s o f o r g a n i c c o a t i n g s . SO2 p e r m e a b i l i t i e s o f alkyd r e s i n s a r e t r e a t e d i n a s e r i e s o f papers^*"!!; however the p u b l i s h e d data are d i f f i c u l t to compare with other data because they a r e not presented i n conventional dimensions. Only s l i g h t l y more data a r e a v a i l a b l e on polymer f i l m s i n g e n e r a l , part o f which have been compiled (Table I I ) . Because o f d i f f e r i n g meas u r i n g c o n d i t i o n s and l a c k i n g informations on these c o n d i t i o n s as w e l l as on the m a t e r i a l s used, even the l i t t l e data on polymer f i l m s given by v a r i o u s f o r e , the only conclusion that SO2 has low p e r m e a b i l i t y i n g l a s s y polymers, very high p e r m e a b i l i t y i n r u b b e r - l i k e polymers, and that there i s a s i g n i f i cant decrease i n SO2 p e r m e a b i l i t y with i n c r e a s i n g polymer c r y s tallinity. Pressure Dependency o f SO? P e r m e a b i l i t y As may be seen from Table I , concentrations o f SO2 i n the atmosphere a r e subjected t o c o n s i d e r a b l e v a r i a t i o n s . Moreover, SO2 concentrations used i n c o r r o s i o n t e s t s a r e l a r g e r by s e v e r a l orders o f magnitude. Therefore, i t becomes h i g h l y questionable whether data obtained a t high SO2 c o n c e n t r a t i o n l e v e l s may be a l s o a p p l i e d t o p r a c t i c a l exposure c o n d i t i o n s . SO2 p e r m e a b i l i t i e s o f a s e r i e s o f polymer f i l m s l i k e p o l y e t h y l e n e , polycarbonate. polyamide-*- as w e l l as p o l y a c r y l a t e and c e l l u l o s e t r i a c e tate-*-" have been shown to depend on SO2 pressure, e s p e c i a l l y at higher SO2 c o n c e n t r a t i o n l e v e l s . In the case o f o r g a n i c coatings such data are not a v a i l a b l e . I t i s t h e r e f o r e recommended t o study SO2 p e r m e a b i l i t y a t low SO2 concentrations comparable to p r a c t i c a l exposure c o n d i t i o n s . 2

Comparison o f SO2 P e r m e a b i l i t y w i t h P e r m e a b i l i t i e s o f Other Gases Contrary to other atmospheric gases l i k e N2, 0 o r CO2, the perm e a b i l i t y o f polymer f i l m s f o r SO2 i s very high (Table I I I ) . Obv i o u s l y the molecular s i z e o f SO2 i s not the dominating f a c t o r for i t s permeation r a t e . As the p e r m e a b i l i t y c o e f f i c i e n t P^ i s defined by the product o f the d i f f u s i o n c o e f f i c i e n t , D, and t h e s o l u b i l i t y , S, the S 0 s o l u b i l i t y o f the polymer f i l m s plays an important r o l e . In f a c t t h e few data published on s o l u b i l i t y o f SO2 i n polymers corroborate t h i s e x p e c t a t i o n . E q u i l i b r i u m s o l u b i l i t y o f SO2 i n p o l y a c r y l a t e was found t o be as h i g h as 21.5% by weight at 760 mmHgl^. j case o f a b i s p h e n o l A polycarbonate, 2

2

n

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

312

EFFECTS OF HOSTILE ENVIRONMENTS

Table I I . SO2 P e r m e a b i l i t i e s o f Polymer Films Polymer Film

Temp. °C

Polyethylene (low density) Polyethylene (high d e n s i t y ) Polyamide (Nylon 11) a) b) Polycarbonate (Lexon) a) b) Vinylidene ChlorideV i n y l c h l o r i d e Copolyme Polyethylene Terephthalat b) Polymethylmethacrylate Polyvinylchloride (rigid) Teflon Polystyrene C e l l u l o s e (cellophane) Cellulose Nitrate Vulcan Rubber S i l i c o n e Rubber

Comparative SO2, 0 , N 2

2

2

2

230

25 22 25 25 25 22 25 22 22

13

61.4 41 131 25

4

20.9 5.68 6.58 2.16 22.4 21,0

0,201 0.132 0.116 4,2 22 52.7 176 1450 11800

145 38

Lit.

12 13 12 13 13

13 14 13 15 13 16 17 14 14

:

PSO /PO 2

Polyethylene (230 m) Polyamide (61 m) Polycarbonate (131 m) Vinylidene Chloride V i n y l C h l o r i d e Copolymer P o l y a c r y l a t e (22.6 m) P o l y a c r y l a t e (22.6 m)

PS0 /PN PS0 /PC0

25 25 25 25 25 25

PSO

Table I I I . and co 2 P e r m e a b i l i t i e s of Polymer Films

Polymer F i l m

1. 2.

Thickness m

2

Lit.

6.8 47 15

12 12 12

65 515 19.2

12 19 19

1

2

2

2

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Influence of Sulfur Dioxide 0

13.5% by weight was o b s e r v e d ^ and explained by electron-donoracceptor complexes. Data o f weight i n c r e a s e o f non-pigmented organic coatings on 24 h r s exposure to SO2 at 760 Hg support these r e s u l t s (Table I V ) . Quite o b v i o u s l y many polymer f i l m s have a high a f f i n i t y to SO2. S 0 a b s o r p t i o n by polybutylmethac r y l a t e f i l m s was s t r o n g l y i n f l u e n c e d by the s o l v e n t used i n f i l m formation (Table V ) . Probably i n t h i s case the t o t a l absorption i s composed o f two concurrent processes: c l u s t e r formation o r f i l l i n g o f h o l e s which obeys a Langmuir isotherm and o r d i n a r y d i s s o l u t i o n which obeys the Henry Law. As has been shown e a r l i e r , f i l m formation may be accompanied by phase s e p a r a t i o n l e a d i n g to incoherent microscopic or submicroscopic solvent i n c l u s i o n s , which may provide the s i t e s f o r the Langmuir a b s o r p t i o n process. Again the questions remain whether both processes a l s o occur at p r a c t i c a l SO2 c o n c e n t r a t i o n l e v e l s and how much SO2 i s absorbed t h e r e . Moreover and s t r e s s - r e l a x a t i o n a s s i s t e to time dependency i n a b s o r p t i o n measurements. 2

2 1

Table IV. Weight Increase o f Polymer Films A f t e r 24 Hours Exposure to Pure SO2 at Atmospheric P r e s s u r e ^ 0

Polymer

Weight Increase %

Cellulose Nitrate PVC-Copolymer Alkyd/Melamine-Resin Epoxy-Resin Polyurethane/Acrylate

3 5 14 11 6

Table V. Influence o f Solvents Used i n F i l m Formation on S 0 Absorption A f t e r 24 Hours o f E x p o s u r e 2

26

PBMA Prepared

from S o l u t i o n With

Mineral S p i r i t s Toluene MIBK Ethylacetate Isopropanol

Weight Increase %

15 16 11 6 12

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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EFFECTS OF HOSTILE ENVIRONMENTS

E f f e c t of Humidity and Pigmentation on SO? P e r m e a b i l i t y I n c r e a s i n g humidity a l s o i n c r e a s e s S 0 p e r m e a b i l i t y . However, no s i g n i f i c a n t e f f e c t s can be observed i f water a b s o r p t i o n of p o l y mer f i l m s i s low. As most o r g a n i c c o a t i n g s absorb only s m a l l a mounts o f water, normal v a r i a t i o n s i n humidity should not s i g n i f i c a n t l y a f f e c t S 0 permeation. As w i t h other f i l l e r s , pigment a t i o n s i g n i f i c a n t l y reduces S 0 p e r m e a b i l i t y 2 2 by the same reason as does polymer c r y s t a l l i n i t y . 2

2

2

Reaction of the F i l m Forming Polymers and Pigments w i t h SO? As a r e s u l t of exposure to S 0 , embrittlement and d i s c o l o r a t i o n of polymer f i l m s have been observed. For chemical r e a c t i o n s to take p l a c e , u s u a l l y the presence o f water, oxygen and sometimes U V - r a d i â t i o n i s r e q u i r e d . With hydrocarbons and U V - r a d i â t i o n , s u l f i n i c a c i d s are formed ethylene i n absence of l i g h t . P o l y e t h y l e n e and polypropylene c r o s s l i n k on exposure to l i g h t and S 0 . Besides a d i r e c t r e a c t i o n w i t h the polymer, a photochemical r e a c t i o n of a c t i v a t e d S 0 w i t h oxygen may lead to formation of ozone which then may a t t a c k polymer f i l m s by o x i d a t i v e d e g r a d a t i o n . A s e r i e s of i n o r g a n i c pigments l i k e chrome y e l l o w , chrome-molybdate and ZnO are a t tacked by S 0 w i t h formation of Cr ( I I I ) s u l f a t e , l e a d s u l f a t e , and ZnS0£ , r e s p e c t i v e l y . Heavy degradation and d i s c o l o r a t i o n were observed on exposure of coated aluminum w a l l panels to S 0 and U V - l i g h t ^ . A c t i v e c o r r o s i o n p r o t e c t i v e pigments l i k e red l e a d may n e u t r a l i z e the c o r r o s i o n - s t i m u l a t i n g a c t i o n of S 0 by formation of s l i g h t l y s o l u b l e PbSO^. As these pigments are i n c r e a s i n g l y p r o h i b i t e d because of t o x i c e f f e c t s and environmental p r o t e c t i o n , i t i s imperative to i n c o r p o r a t e other SO9 scavenging components i n organic coatings to i n c r e a s e t h e i r p r o t e c t i o n e f ficiency. 2

2

2

2

2

2

2

Literature Cited

1) J. Baumuller and U. Hoffmann, Bauphysik, 1, 22 (1982). 2) German Standardization DIN 50 018. 3) H. C. Wohlers andG.B. Bell, "Literature review of metropolitan air pollutant concentrations", Stanford Res. Inst. Report, 1958. 4) J. Ruf, "Korrosion", Schutz durch Lacke und Pigmente, Verlag W. A. Colomb, Stuttgart, 1972. 5) L. G. Johanson and N. G. Vannerberg, Werkstoffe und Korrosion, 32, 265 (1981). 6) K. Barton, S. Bartonova and E. Beranek, Werkstoffe und Korrosion, 25, 659 (1974). 7) H. Schwarz, Werkstoffe und Korrosion, 16, 93 (1965). 8) A. L. Glass and J. Smith, J. Paint Technology, 39, 490 (1967).

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

18. FUNKE AND HAAGEN Influence of Sulfur Dioxide

315

9) M. Svoboda, H. Klicova and B. Knapek, FarbeundLack, 74, 659 (1968). 10) M. Svoboda, H. Klicova and B. Knapek, J. Oil Chem. Assoc., 52, 677 (1969). 11) M. Svoboda, H. Klicova and B. Knapek, Farbe und Lack, 75, 121 (1969). 12) E. G. Davis and M. L. Rooney, Kolloid Ztschr., Ztschr. f. Polymere 249, 1043 (1971). 13) Ε. G. Davis, M. L. Rooney and P. L. Larkins, J. Appl. Polym. Sci., 19, 1829 (1975). 14) M. Benarie and Bui-the-Chuong, Atmos. Environ., 3, 574 (1969). 15) Β. E. Saltzman, C. R. Feldmann and A. E. O'Keefe, Environ. Sci.Technol.,5, 1121 (1974). 16) J. Hanonsek and L. Herynk, Chem. Listy, 56, 376 (1962). 17) P. Y. Hsieh, J. Appl Polym Sci. 7 1743 (1963) 18) R. M. Felder, R Data, 20, 235 (1975). 19) D. L. Kuehne and S. K. Friedlander, Ind. Eng. Chem. Process Dev., 19, 609 (1980). 20) Ε. G. Davis and M. L. Rooney, J. Polym. Sci., 10, 2325 (1972). 21) W. Funke, J. Oil Chem. Assoc., 59, 398 (1976). 22) M. Svoboda, G. Klicova and B. Knapek, Zashchita Metallov, 9, 301 (1973). 23) H. H. G. Jellinek, F. Flajsman and F. J. Kryman, J. Appl. Polym. Sci., 13, 107 (1969). 24) S. Torlaski, L. Caggiati and G. Zorzella, "Fatipec Con­ ference Florence 1972", Conference book p. 207, 1972. 25) H. Haagen - Unpublished results. 26) H. Haagen -.Farbe und Lack, in print. RECEIVED April4,1983

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

19 Photochemical Degradation and Biological Defacement of Polymers P. D. GABRIELE, J. R. GEIB, R. M. IANNUCCI, and W. J. REID Ciba-Geigy Corporation, Additives Department, Ardsley, NY 10502

Engineering plastic ing exposed to increasingly more hostile environments as they replace and protect more wood and metal products, especially in exterior applications. When exposed outdoors these plastics must withstand the concerted effects of moisture, oxygen, heat, ultraviolet light, and micro-organisms in order to perform their designed function. The combined effects of the first four factors, i.e., moisture, oxygen, heat and UV light, can result in photooxidation in the polymer surface. Eventually, erosion and microfracture of the polymer surface ensues, thus creating a microenvironment which is conducive to moisture and "dirt" accumulation. Also, the photooxidation leads to high concentrations of a variety of carbonyl groups which cause the surface to be hydrophilic. This hydrophilicity allows the polymer surface to absorb moisture causing it to swell and result in additional stress cracking. The surface microenvironment provides an ideal atmosphere for mildew growth, i.e., free moisture, carbon and nutrient sources which accumulate during the weathering process. The polymers and coatings which we have examined have had to undergo significant surface deterioration prior to the time that mildew could undergo active growth on the surface. By proper stabilization of the polymers and coatings with benzotriazole UV absorbers, hindered amine light stabilizers (HALS), or combination of the two stabilizers, the surfaces of the polymers and coatings could be maintained and thus active mildew growth prevented. 0097-6156/ 83/0229-0317S06.00/0 © 1983 American Chemical Society

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Engineering p l a s t i c s and organic coatings are being exposed to i n c r e a s i n g l y more h o s t i l e environments as they r e p l a c e and protect more wood and metal products, e s p e c i a l l y i n e x t e r i o r app l i c a t i o n s . When exposed outdoors these m a t e r i a l s must withstand the concerted e f f e c t s of moisture, oxygen, heat, u l t r a v i o l e t l i g h t , and micro-organisms i n order to perform t h e i r designed f u n c t i o n . Photodegradation of p l a s t i c m a t e r i a l s that have been exposed to outdoor c o n d i t i o n s has been studied e x t e n s i v e l y (I). B i o l o g i c a l degradation of p l a s t i c m a t e r i a l s has a l s o been widely studied 02,3^4). Recently, we reported the r e s u l t s o f numerous s t u d i e s o f d i f f e r e n t p l a s t i c m a t e r i a l s that had been exposed outdoors i n F l o r i d a ( 5 ) . The purpose of these s t u d i e s had been to show the e f f e c t i v e n e s s o f hindered amine l i g h t s t a b i l i z e r s (HALS), t y p i c a l l y b i s [ 2 , 2 , 6 , 6 - t e t r a m e t h y l - 4 - p i p e r i d i n y l ] s e b a c a t e (LS I ) , and b e n z o t r i a z o l e UV absorbers, t y p i c a l l y 2(2'-hydroxy5'-methyl-phenyDbenzotriazol n a t i o n with each other p l a s t i c m a t e r i a l s . We had shown that the o p t i m a l l y s t a b i l i z e d samples of a "weatherable" s t y r e n i c terpolymer (an ABS-type p l a s t i c that contained a saturated rubber i n place of the butadiene) s t a b i l i z e d with a combination of 0.5% LS I and 0.5% LS II had been able to maintain i t s c o l o r , appearance, s u r f a c e i n t e g r i t y , and p h y s i c a l p r o p e r t i e s through four years o f outdoor weathering i n F l o r i d a . The c o n t r o l with no l i g h t s t a b i l i z e r s was p i t t e d and h e a v i l y encrusted with mildew. Other samples i n t h i s study which contained only 0.5% HALS or only 0.5% b e n z o t r i a z o l e , were a l s o h e a v i l y encrusted with mildew at t h i s same time p e r i o d , 4 years, thus i n d i c a t i n g that n e i t h e r component of the blend was f u n c t i o n i n g as a f u n g i c i d e . A l s o , mildew was a c t i v e l y growing on the rough cut sides of the o p t i m a l l y l i g h t s t a b i l i z e d samples, again i n d i c a t i n g that n e i t h e r of the l i g h t s t a b i l i z e r s alone or i n combination with each other was a c t i n g as a f u n g i cide. (Figure 1). Samples o f polypropylene s t a b i l i z e d with j u s t LS I had a l s o been able to maintain t h e i r c o l o r , appearance, surface i n t e g r i t y , and p h y s i c a l p r o p e r t i e s through 2.5 years of outdoor weathering i n F l o r i d a . Moreover, t h e r m o p l a s t i c p o l y urethane m a t e r i a l s s t a b i l i z e d with j u s t LS I a l s o had e x c e l l e n t performance through s i x months outdoor weathering i n F l o r i d a . A l l of the above p l a s t i c m a t e r i a l s that contained no l i g h t s t a b i l i z e r s , low amounts of the p r e f e r r e d l i g h t s t a b i l i z e r s , or other types o f l i g h t s t a b i l i z e r s had extensive s u r f a c e e r o s i o n and heavy i n f e s t a t i o n s o f micro-organisms, most notably mildew (Aureobasidium p u l l u l a n s ) , a f t e r the same periods of outdoor exposure. Mildew defacement of organic coatings and p l a s t i c s has long been a major problem of the organic coatings and p l a s t i c s indust r i e s . Aureobasidium p u l l u l a n s i s the major c a u s i t i v e organism

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

GABRIELE ET AL.

Photochemical and Biological Degradation

Figure 1. illustration of the non-biocidal activity of the hindered amine light stabilizer LSI and the benzotriazole UV absorber LS Hon a modified styrenie terpolymer. Key: left, unaged: and right, Florida exposure for 500,000 langleys (approx. 4 years).

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

320

EFFECTS OF HOSTILE ENVIRONMENTS

r e s p o n s i b l e f o r t h i s defacement (5-8 ). It was the primary organism i d e n t i f i e d as being r e s p o n s i b l e f o r the b i o l o g i c a l defacement i n the three polymer systems without l i g h t s t a b i l i z e r s that we had p r e v i o u s l y examined. U n t i l now, the approach to solve t h i s problem has been to incorporate a f u n g i c i d e i n t o a c o a t i n g formulation or compound a f u n g i c i d e i n t o a p l a s t i c . Although t h i s technique had success f o r short s e r v i c e time p e r i o d s , the f u n g i c i d e may be vaporized or leached from the coatings and p l a s t i c s over long time p e r i o d s . In a d d i t i o n , the b i o l o g i c a l a c t i v i t y of most non-mercurial organic and organomet a l l i c f u n g i c i d e s are s i g n i f i c a n t l y destroyed by photo-oxidation from the u l t r a v i o l e t l i g h t present i n t e r r e s t r i a l s o l a r r a d i a tion. Once the c o n c e n t r a t i o n of the f u n g i c i d e drops below c r i t i c a l l e v e l s , mildew can attack the coating or p l a s t i c s u r face ( 6 ) . The combined e f f e c t l i g h t can r e s u l t i n photooxidatio E v e n t u a l l y , e r o s i o n and m i c r o f r a c t u r e of the polymer ensues, thus c r e a t i n g a microenvironment which i s conducive to moisture and " d i r t " accumulation. A l s o , the photooxidation leads to high concentrations of a v a r i e t y of earbonyl groups which cause the surface to be very h y d r o p h i l i c . This h y d r o p h i l i c i t y allows the polymer surface to absorb moisture causing i t to s w e l l and r e s u l t i n a d d i t i o n a l s t r e s s c r a c k i n g . The surface microenvironment provides an i d e a l atmosphere f o r mildew growth, i . e . f r e e moisture, carbon, and n u t r i e n t sources which accumulate during the weathering process. The polymers and coatings which we have examined have undergone s i g n i f i c a n t surface d e t e r i o r a t i o n p r i o r to the time of mildew appearance. By proper s t a b i l i z a t i o n of the polymers and coatings with b e n z o t r i a z o l e UV absorbers, hindered amine l i g h t s t a b i l i z e r s (HALS), or combination of the two s t a b i l i z e r s , the surfaces of the polymers and coatings could be maintained and thus a c t i v e mildew growth prevented. In a d d i t i o n , by preventing the photooxidation of the surface of the p l a s t i c by the a d d i t i o n of the above l i g h t s t a b i l i z e r s , both the appearance and the p h y s i c a l p r o p e r t i e s of the polymers are preserved f o r s i g n i f i c a n t l y longer periods of time than i f they were u n s t a b i l i z e d or s t a b i l i z e d with other types of s t a b i l i z e r s . In the current study, samples of impact polystyrene that contained a combination of l i g h t s t a b i l i z e r s LS I and LS II and samples that contained no l i g h t s t a b i l i z e r s were weathered outdoors i n F l o r i d a and were monitored f o r changes i n p h y s i c a l appearance and f o r changes i n the chemical s t r u c t u r e of the s u r face by use of a m u l t i p l e i n t e r n a l r e f l e c t a n c e IR s p e c t r o photometer. A l s o , samples of a thermoplastic polyurethane that was s t a b i l i z e d with j u s t LS I and samples that contained no l i g h t s t a b i l i z e r s were weathered and monitored i n the same way as the impact p o l y s t y r e n e . We hope to e s t a b l i s h at what point

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

19.

GABRIELE ET A L .

Photochemical and Biological Degradation

i n the photodegradation of a polymer i t becomes s u s c e p t i b l e to a t t a c k by microorganisms and e s t a b l i s h what e f f e c t the l i g h t s t a b i l i z e r s have i n preventing or d e l a y i n g the photodegradation and subsequent a t t a c k by the microorganisms.

EXPERIMENTAL 1. P r e p a r a t i o n and L i g h t Exposure o f Polymer Samples. (a) Impact P o l y s t y r e n e : L i g h t s t a b i l i z e r s were compounded into commercial impact p o l y s t y r e n e (IPS) by a commerc i a l processor. The samples were i n j e c t i o n molded i n to 1/8 inch t h i c k d i s c s and were subsequently weathered at 45° f a c i n g south i n F l o r i d a . Sample 1 was impact polystyrene which contained no l i g h t s t a b i l i z e r s and Sample 2 was impac LS I plus 0.5% (b) Thermoplastic Urethane F i l m s : Commercial thermoplast i c polyurethane (Estane 5707 from B . F. Goodrich) was d i s s o l v e d i n a 1:1 (w/w) mixture o f DMF/toluene to form a 20% s o l u t i o n . L i g h t s t a b i l i z e r s were separatel y d i s s o l v e d i n a minimum o f the 1:1 solvent mixture and then were added t o the r e s i n s o l u t i o n . Drawdowns of the r e s i n s o l u t i o n s were prepared to o b t a i n a r e s u l t a n t 1.5 m i l t h i c k f i l m a f t e r d r y i n g . The drawdowns were f l a s h e d f o r f i v e minutes at room temperature and then were f o r c e d - a i r d r i e d f o r 15 minutes at 75°C. Subsequently, the f i l m s were exposed at 45° under glass f a c i n g south i n F l o r i d a . Sample 3 was a thermop l a s t i c polyurethane which contained no l i g h t s t a b i l i z e r s and Sample 4 was a thermoplastic polyurethane which contained 0.5% LS I . 2.

Scanning E l e c t r o n Microscope

(SEM).

Each sample was cemented t o a specimen holder and then was coated with approximately 200 8 o f aluminum i n an EFFA Rotary Vacuum Evaporator. The photomicrographs were obt a i n e d from a Cambridge Model S180 Scanning E l e c t r o n Microscope. 3.

M u l t i p l e I n t e r n a l R e f l e c t a n c e (MIR) I n f r a r e d Spectroscopy. A l l samples were run on a P e r k i n Elmer 281 with data s t a t i o n using the m u l t i p l e i n t e r n a l r e f l e c t a n c e attachment (part #186-0382). A 45° r e f l e c t i o n angle was used f o r a l l samples.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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EFFECTS OF HOSTILE ENVIRONMENTS

RESULTS The samples of impact polystyrene and a t h e r m o p l a s t i c polyurethane were weathered i n F l o r i d a , and then examined with a scanning e l e c t r o n microscope and with a m u l t i p l e i n t e r n a l r e f l e c t a n c e (MIR) spectrophotometer with the f o l l o w i n g results. W i t h i n s i x months of outdoor exposure i n F l o r i d a , the samples of both IPS and polyurethane that contained no l i g h t s t a b i l i z e r s had a c t i v e growths of mildew p r e s e n t . No mildew was evident on the s t a b i l i z e d samples a f t e r the same period of exposure. ( F i g u r e s 2, 3 , 4) Photos l a and 2a are the photomicrographs of the unexposed impact polystyrene and i l l u s t r a t e the i n i t i a l i n t e g r i t y of the polymer s u r f a c e . Spectra l a i s a MI Spectra 2a i s a MIR s p e c t r t a i n e d l i g h t s t a b i l i z e r s . Note the intense aromatic r i n g b r e a t h i n g modes between approximately 1600 cm and 1400 cm ( 9 ) . Photos lb and 2b are photomicrographs of IPS samples that had been weathered outdoors i n F l o r i d a f o r three months. Spectra 1^ i l l u s t r a t e s the b u i l d u p of earbonyl groups at about 1700 cm a f t e r three months outdoor exposure of t i p IPS. Note the degree of band broadening i n the 1600 cm r e g i o n which i s probably due to a r y l earbonyl f o r m a t i o n . Photo 1c i s a photomicrograph of IPS that contained no l i g h t s t a b i l i z e r s which was exposed outdoors i n F l o r i d a f o r s i x months. Note the t o t a l l o s s of surface i n t e g r i t y i n c l u d ing deep surface c r a z e s . This photo a l s o shows the mildew that was v i s u a l l y present along with t h e i r t y p i c a l hyphal structures. Photo 2c i s a photomicrograph of IPS that contained the combination of l i g h t s t a b i l i z e r s (LS I and LS I I ) which was exposed outdoors i n F l o r i d a f o r s i x months. Note the minimal amount of surface d e t e r i o r a t i o n . Some surface d i r t i s present i n the photo. Spectra 1c corresponds to Photo l c . No|e the intense d e velopment of a earbonyl band around 1620 cm . A f t e r s i x months outdoor weathering the peaks r e l a t e d to the aromatic s k e l e t a l r i n g b r e a t h i n g mode have been masked. Spectra 2c corresponds to Photo 2 c . A s i g n i f i c a n t e a r bonyl peak has formed, but the aromatic s k e l e t a l r i n g b r e a t h ing mode peaks are s t i l l q u i t e apparent. Photos 3a and 4a are the photomicrographs of the unexposed t h e r m o p l a s t i c polyurethanes and i l l u s t r a t e the i n i t i a l i n t e g r i t y of the polymer s u r f a c e . Spectra 3A (neat, no l i g h t s t a b i l i z e r ) and 4a (0.5% LS I) represent the MIR s p e c t r a of the unexposed p o l y e s t e r urethane.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Photochemical and Biological Degradation

323

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Figure 2. SEM photomicrographs at 600x (left) and IR spectra (right) of impact polystyrene with no light stabilizers. The samples were exposed in Florida at a 45° angle facing south. SEM shows the presence of mildew.

In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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In The Effects of Hostile Environments on Coatings and Plastics; Garner, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.

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Photochemical and Biological Degradation

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