1 0 0 w 4.f Epoxy Resin Chemistry 1 1 0 9- 7 9 1 k- b 1/ 2 0 1 0. 1 oi: d 9 | 7 9 1 3, er b m e c e D e: at D n o ati c bli u P 1 0 0 w 4.f 1 1 0 9- 7 9 1 k- b 1/ 2 0 1 0. 1 oi: d 9 | 7 9 1 3, er b m e c e D e: at D n o ati c bli u P Epoxy Resin Chemistry Ronald S. Bauer, EDITOR Shell Development Company 1 0 0 w 4.f 1 1 0 9- Based on a symposium sponsored 7 9 1 k- b by the Division of 1/ 2 0 1 10. Organic Coatings and Plastics oi: d 79 | at the 176th Meeting of the 9 1 3, er American Chemical Society, b m e c e D Miami Beach, Florida, e: at D n September 11-15, 1978. o ati c bli u P ACS SYMPOSIUM SERIES 114 AMERICAN CHEMICAL SOCIETY WASHINGTON, D.C. 1979 1 0 0 w 4.f 1 1 0 9- 7 9 1 k- 1/b Library of Congress CIP Data 2 0 Epoxy resin chemistry. 1 0. (ACS symposium series; 114 ISSN 0097-6156) oi: 1 Includes bibliographies and index. d 1. Epoxy resins—Congresses. 79 | I. Bauer, Ronald S., 1932- . II. American Chemi 9 1 cal Society. Division of Organic Coatings and Plastics 3, Chemistry. III. Series: American Chemical Society. er ACS symposium series; 114. b m e TP1180.E6E59 668'.374 79-21858 ec ISBN 0-8412-0525-6 ASCMC8 114 1-271 1979 D e: at D on Copyright © 1979 ati blic American Chemical Society u P 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 works, for resale, or for information storage and retrieval systems. 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, repro duce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. PRINTED IN THE UNITED STATES OF AMERICA American Chemical Society Library 1155 16th St. N. W. Washington, D. C. 20036 ACS Symposium Series 1 0 0 w 4.f M. Joan Comstock, Series Editor 1 1 0 9- 7 9 1 k- b 1/ 02 Advisory Board 1 0. 1 oi: Kenneth B. Bischoff James P. Lodge d 9 | 97 Donald G. Crosby John L. Margrave 1 3, er Robert E. Feeney Leon Petrakis b m e c De Jeremiah P. Freeman F. Sherwood Rowland e: at D E. Desmond Goddard Alan C. Sartorelli n o cati Jack Halpern Raymond B. Seymour bli u P Robert A. Hofstader Aaron Wold James D. Idol, Jr. Gunter Zweig FOREWORD 1 0 0 w 4.f The ACS SYMPOSIUM SERIES was founded in 1974 to provide 11 a medium for publishing symposia quickly in book form. The 0 9- format of the Series parallels that of the continuing ADVANCES 7 9 1 IN CHEMISTRY SERIES except that in order to save time the k- 1/b papers are not typeset but are reproduced as they are sub 2 0 mitted by the authors in camera-ready form. Papers are re 1 10. viewed under the supervision of the Editors with the assistance oi: of the Series Advisory Board and are selected to maintain the d 9 | integrity of the symposia; however, verbatim reproductions of 7 9 1 previously published papers are not accepted. Both reviews 3, er and reports of research are acceptable since symposia may b m embrace both types of presentation. e c e D e: at D n o ati c bli u P PREFACE ^ince their commercial introduction into the United States in the late ^ 1940's, epoxy resins have established themselves as unique building blocks for high performance coatings, adhesives, and reinforced plastics. Over the past five years epoxy resin sales have experienced an annual growth rate of about 8%. In 1978, production in this country exceeded 310 million pounds, and domestic sales were greater than 280 million 1 0 pounds. This sustained growth of epoxy resins is a result of the wide 0 pr range of properties that can be achieved with these versatile materials; 4. 11 uses range from coatings for the ubiquitous beverage can to high per 0 9- formance adhesions in spacecraft as well as for encapsulating their 7 9 1 sophisticated electronic components. k- 1/b Work still continues as pressures for more environmentally acceptable 2 0 and energy efficient systems, and demands for even higher performance, 1 10. challenge the polymer chemist. This volume covers some of the new oi: resins, curing agents, and application techniques along with new ideas d 9 | about the chemistry and properties of existing epoxy resin systems. 7 9 1 Although comprehensive coverage of this field is not possible in our 3, er symposium, it is hoped the papers presented here will help stimulate b m polymer chemists to answer the challenges facing them. e c e D e: Shell Development Company RONALD S. BAUER at D Houston, Texas 77001 n o May 21, 1979 ati c bli u P ix 1 The Photoinitiated Cationic Polymerization of Epoxy Resins J. V. CRIVELLO and J. H. W. LAM General Electric Corporate Research and Development Center, Schenectady, NY 12301 1 0 0 h c 4. The importance of epoxy resins in the fabrication of surface 1 1 coatings is well recognized in the coatings and plastics industry. 0 9- In fact, the chief use of epoxy resins, amounting to over 100 7 19 million pounds last year, was for coating applications (1). Tra bk- ditionally, these coatings have been applied from solvents and 21/ cured by a baking process. Current efforts to reduce the amount 0 1 of energy required to carry out coating processes as well as an 0. 1 increasing concern for the environment have provided the impetus oi: to begin the search for new curing chemistry and coating applica d 9 | tion techniques which circumvent these problems. 7 9 Ultraviolet curing has emerged as a rapidly growing method 1 3, for the fabrication of essentially pollution-free coatings, having er only a fraction of the energy requirements of traditional ther b m mally cured materials. At the same time, the generally excellent e ec properties of the coatings which are obtained using uv curing D e: resins together with their high application and cure speeds have at made it attractive for many industries to install uv-cure lines. D n While the bulk of the work in uv curing to date has involved o ati the radical polymerization of vinyl compounds, during the past c bli five years discovery of several new photoinitiator compounds now u P makes it possible to effect the uv-cure of epoxy resins by a cationic process. With such systems, solventless liquid epoxy resins can be cured continuously at very high line speeds using approximately one tenth the energy which would be consumed by a comparable thermal process. The first of these new photoiniti ators are the aryldiazonium salts (I) (2_>3.»4,5j. when these com pounds are irradiated using uv light, a fluoroaromatic compound, nitrogen and the strong Lewis acid, boron trifluoride, are pro duced (equation 1). Ar-N+EN BF" — > Ar-F + N + BF^ (1) 4 2 I If the photolysis of an aryldiazonium salt is conducted in the 0-8412-0525-6/79/47-114-001$05.00/0 © 1979 American Chemical Society 2 EPOXY RESIN CHEMISTRY presence of an epoxy resin, boron trifluoride catalyzes the cationic polymerization of the resin. Due to the production of nitrogen as a byproduct of the photolysis of aryldiazonium salts, the major uses of coating systems employing these photoinitiators lies primarily in thin film applications such as container coat ings [6) and photoresists (7J. Recently, we have reported that diaryliodonium salts (II) are a second class of highly efficient photoinitiators for the Ar-I-Ar' X" = BF", AsF , PF , SbCl , etc. 4 6 6 6 II 1 0 h0 cationic ring opening polymerization of epoxy resins (8,9J. c 4. Parallel work in two other laboratories has led to the same con 1 01 clusion (10, ]V). Mechanistic studies have shown that on photol 79- ysis, diaryliodonium salts liberate strong Br0nsted acids of the 9 1 type, HX, which subsequently initiate cationic polymerization. k- b In this paper, we would like to report some recent work 1/ 2 which has led to the development of triarylsulfonium salts (III) 0 0.1 as a third class of useful photoinitiators for cationic polymeri doi: 1 pzaotliyomn erainzda tiino n paofr tiecpuolxaird, esd. escribe their application to the 9 | 97 ^r1 1 er 3, Ar-S+ X" b m Ar" e c e D e: III at D n Results and Discussion o ati c bli In our laboratory, we have found that triarylsulfonium Pu salts (III) in which the anions are of the type BF " AsF", PF", 6 6 SbF ~ etc., are excellent photoinitiators for the polymerization of epoxy resins as well as a variety of other monomers (12, 13). Similar results have also been reported by another group of investigators (14). Triarylsulfonium salts may be conveniently prepared via a number of synthetic routes. In equations 2, 3 and 4 are shown three of the most direct preparative methods. 6ArH + SC1 + 3C1 A1C13 ^ 2(Ar)S+Cl" + 6HC1 (2) 2 2 2 3 Ar Ar ^S-* 0 + Ar'-MgBr benzene ^+. - " + gBrOH (3) > s Ar x M Ar' ref 1 ux Ar 1. CRIVELLO AND LAM Photoinitiated Cationic Polymerization 3 Cu11 (cat) (Ar)S + (Ar')I+ X" > ArAr»S+ X" + Ar'I (4) 2 2 2 Although the reaction shown in equation 2 is simple and direct, the products which are obtained are generally impure (15). The condensation of diarylsulfoxides with Grignard reagents (equation 3) gives pure triarylsulfonium salts; however, the overall yields are generally of the order of 20-30% (16). In a very recent publication from this laboratory,we described a general synthesis which affords these compounds in high yields (17_). This new route involves the copper (II) catalyzed arylation of diaryl iodonium salts with diarylsulfides (equation 4). Both of the methods shown in equations 2 and 3 give rise to 01 triarylsulfonium halides which are inactive as photoinitiators 0 h for cationic polymerization. These salts must, therefore, be c 4. converted to the corresponding salts in which the anion is of 1 01 the type X" = BF4", ASF5", PFc", etc. This conversion may be 79- accomplished using either of the two methods shown in equation 5. 9 1 k- Ago 1/b ? _> Ar3S+ OH" + AgCl 2 0 1 0. 1 oi: d 9 | (5) 7 9 1 3, Using the above synthesis, a wide variety of triarylsulfon ber ium salt photoinitiators can be prepared. In Table 1 are shown m e some representative triarylsulfonium salt photoinitiators which c De were prepared during the course of this research. All the com e: pounds in this table are well characterized crystalline com Dat pounds with well defined melting points, elemental analyses, on ultraviolet, proton, and 1 3C nmr spectra (1_7). The ability ati of triarylsulfonium salts bearing non-nucleophilie counterions to c bli serve as photoinitiators is completely general and includes all u P the symmetrical, unsymmetrical, substituted and unsubstituted as well as polynuclear and heterocyclic salts shown in Table 1. In contrast to radical photoinitiators which are also gen erally thermally unstable, triarylsulfonium salts display a sur prising level of thermal stability. Figure 1 shows the thermo- gravimetric analysis curves for triphenylsulfoniurn hexafluoro- arsenate performed in air and nitrogen at a heating rate of 10°C/minute. In both cases, thermal decomposition is not ob served below 350°C. This high level of thermal stability is reflected in the extremely long shelf lifes of epoxy resins sensitized with triarylsulfonium salt photoinitiators. Figure 2 shows the plots of the increase in solution viscosityversus + time in months for various concentrations of (Cs^JqS ASF5" in the highly reactive bisepoxide, 4-vinylcyclohexene dioxide. Only a slight increase in the overall solution viscosity was noted