Characterization of Highly Cross-linked Polymers PDF
Preview Characterization of Highly Cross-linked Polymers
Characterization of Highly Cross-linked Polymers In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 243 ACS S Y M P O S I U M S E R I E S Characterization of Highly Cross-linked Polymers S. S. Labana, EDITOR Ford Motor Company R Ford Motor Company Based on a symposium sponsored by the Division of Organic Coatings and Plastics Chemistry at the 185th Meeting of the American Chemical Society, Seattle, Washington, March 20-25, 1983 American Chemical Society, Washington, D.C. 1984 In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. Library of Congress Cataloging in Publication Data Characterization of highly cross-linked polymers. (ACS symposium series, ISSN 0097-6156; 243) Includes papers presented at the Symposium on Highly Cross-linked Polymers sponsored by the Division of Organic Coatings and Plastic t th 185th meeting of the American Chemica Wash., March 20-25, 1983." Bibliography: p. Includes indexes. 1. Polymers and polymerization—Congresses. I. Labana, Santokh S., 1936- . II. Dickie, R. Α., 1940- . III. Symposium on Highly Cross-linked Polymers (1983: Seattle, Wash.) IV. American Chemical Society. Division of Organic Coatings and Plastics Chemistry. V. Series. QD380.C45 1984 547.7 83-25733 ISBN 0-8412-0824-7 Copyright © 1984 American Chemical Society All Rights Reserved. The appearance of the code at the bottom of the first page of each chapter in this volume indicates the copyright owner's consent that reprographic copies of the chapter may be made for personal or internal use or for the personal or internal use of specific clients. 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The citation of trade names and/or names of manufacturers in this publication is not to be construed as an endorsement or as approval by ACS of the commercial products or services referenced herein; nor should the mere reference herein to any drawing, specification, chemical process, or other data be regarded as a license or as a conveyance of any right or permission, to the holder, reader, or any other person or corporation, to manufacture, reproduce, use, or sell any patented invention or copyrighted work that may in any way be related thereto. Registered names, trademarks, etc., used in this publication, even without specific indication thereof, are not to be considered unprotected by law. PRINTED IN THE UNITED STATES OF AMERICA In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. ACS Symposium Series M. Joan Comstock, Series Editor Advisory Board Robert Baker y U.S. Geological Survey Carnegie-Mellon University Martin L. Gorbaty Theodore Provder Exxon Research and Engineering Co. Glidden Coatings and Resins Herbert D. Kaesz James C. Randall University of California—Los Angeles Phillips Petroleum Company Rudolph J. Marcus Charles N. Satterfield Office of Naval Research Massachusetts Institute of Technology Marvin Margoshes Dennis Schuetzle Technicon Instruments Corporation Ford Motor Company Research Laboratory Donald E. Moreland USDA, Agricultural Research Service Davis L. Temple, Jr. Mead Johnson W. H. Norton J. T. Baker Chemical Company Charles S. Tuesday General Motors Research Laboratory Robert Ory USDA, Southern Regional C. Grant Willson Research Center IBM Research Department In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. FOREWORD The ACS SYMPOSIUM SERIES was founded in 1974 to provide a medium for publishing symposia quickly in book form. The format of the Series parallels that of the continuing ADVANCES IN CHEMISTTIY SERIE papers are not typese mitted by the authors in camera-ready form. Papers are re viewed 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 Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. PREFACE have long been an important class of materials CROSS-LINKED POLYMERS and are used in a diverse assortment of applications including organic coatings, fiber-reinforced plastics, elastomers, and adhesives. Characteriza tion of these materials has always been difficult, especially for the more highly cross-linked materials general intractability. Considerabl progres year developing theoretical approaches to the description of the molecular struc ture of cross-linked polymers; several chapters describe the recent progress in this important area. Light scattering and rheological characterization tech niques have been applied to cross-linking systems in the pre-gel state. Macroscopic mechanical characterization of cross-linked polymers has been the subject of many investigations; fracture behavior, relationships between molecular structure, morphology, and mechanical properties, and the depend ence of properties on thermal history are discussed by several authors. Not all network formation occurs through formation of chemical bonds; in one chapter in this volume, neutron scattering results suggest the formation of correlation networks in certain polymer blends. Characterization of the chemical structure of highly cross-linked poly mers, and of the chemical changes that accompany degradation processes, relies on spectroscopic methods. Solid-state nuclear magnetic resonance techniques have the potential to allow a more detailed characterization than before possible of the chemical environment and structure of chemical cross links in elastomers and thermoset epoxies. Degradation processes in cross- linked systems have been studied by using infrared spectroscopy, solid-state NMR, and electron spin resonance. It is a pleasure to acknowledge the support of the Ford Motor Com pany. We also wish to thank A. Oslanci and M. Dvonch for their secretarial assistance. Finally, sincere thanks to the authors who have made this volume possible through their hard work and cooperation. S. S. LABANA R. A. DICKIE Ford Motor Company Dearborn, Michigan November 3, 1983 ix In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 1 Formation and Properties of Polymer Networks Experimental and Theoretical Studies J. L STANFORD, R. F. T. STEPTO, and R. H. STILL Department of Polymer Science and Technology, The University of Manchester Institute of Science and Technology, Manchester, M6O 1QD, England Experimental results on reactions forming tri- and tetrafunctional polyurethan ester networks ar particula ation of intramolecular reaction and its effect on shear modulus of the networks formed at complete reaction. The amount of pre-gel intramolecular reaction is shown to be significant for non-linear polymerisations, even for reactions in bulk. Gel -points are delayed by an amount which depends on the dilution of a reaction system and the functionalities and chain structures of the reactants. Shear moduli are generally markedly lower than those expected for the perfect networks corresponding to the various reaction systems, and are shown empirically to be closely related to amounts of pre-gel intramolecular reaction. Deviations from Gaussian stress-strain behaviour are reported which relate to the low molar-mass of chains between junction points. Finally, a rate theory of random polymerisation is described which enables the moduli of networks to be predicted from the molar mass, functionality, chain structure and initial dilution of the reactants used for network formation. This paper presents a survey of published and more recent work on correlations between network properties and reactant structures and reaction conditions, and extends the work presented in recent publications (122)· ^ne reaction systems used have been poly- 9 9 oxypropylene (POP) triols or tetrols and mixtures of diols and triols of various molar masses reacting with diisocyanates (to give polyurethanes) or diacid chlorides (to give polyesters). Systems have been chosen so that like groups had equal reactivit ies and reactions have been carried out in bulk and at various dilutions in inert solvents using equimolar amounts of the different reactive groups. Experimentally, emphasis has been placed on the extent to which pre-gel intramolecular reaction 0097-6156/ 84/0243-0001 $06.00/0 © 1984 American Chemical Society In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 2 HIGHLY CROSS-LINKED POLYMERS and the consequent delay in the gel point beyond the ideal, Flory-Stockmayer gel point (4,5) defines the physical properties of the networks formed at complete reaction. Intramolecular reaction can introduce elastically ineffective loops into a rubbery network. In general, loops produce the opposite effects on physical properties to those expected from entanglements. Theoretical approaches are outlined which attempt to account for intramolecular reaction in terms of reactant structure (function ality, molar mass, and chain structure) and reaction conditions (concentrations of reactants). The approaches allow the prediction of gel points accounting for pre-gel intramolecular reaction. Additionally, account of pre-gel and post-gel intra molecular reaction allows the prediction of shear modulus at complete reaction. Pre-Gel Intramolecular Reactio Previous studies(6») have shown how the number fraction of ring structures formed during irreversible linear random polymerisa tions leading to polyurethanes may be measured. The work has been extended(7,8) to non-linear polyurethane formation using hexa- methylene diisocyanate(HDI) and POP triols. For non-linear polymerisations, i t is found that the number of ring structures per molecule(Np) is always significant, even in bulk reactions. For example, Figure 1 shows N versus extent of reaction(p), for r linear and non-linear polyurethane-forming bulk reactions with approximately equimolar concentrations of reactive groups(2,,6^,1). The much larger values of N in the non-linear compared with the r linear polymerisation are due to the larger number of opportunities per molecule for intramolecular reaction in the former type of polymerisation. However, the other factors influencing intra molecular reaction in the two systems, particularly the number of bonds(v) in the chain forming the smallest ring structure predict more intramolecular reaction in the linear system. A detailed discussion of these factors has been given elsewhere(2.). It should be noted that i t is not possible to reduce the number of ring structures formed in such reaction systems as the amounts of intermolecular reaction relative to intramolecular reaction are at a maximum for reactions in bulk. The gel point of the non-linear system shown in Figure 1 was at ρ = 0.765 compared with the value of 0.707 expected in the absence of intramolecular reaction. Thus, although ρ at gel is only about Q% higher than expected, N = 0.3 at ρ = 0.765, r showing that at gel about one molecule in three contained a ring structure. Such ring structures or loops can have marked effects on the properties of networks formed at complete reaction(1,2,9- 12). Developments in the theoretical aspects of the work, allowing prediction of N, the gel point, and the shear moduli r of networks formed at complete reaction are presented in the last section of the present paper. In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984. 1. STANFORD ET AL. Formation and Properties of Networks 3 ΟΛ - 0.3 non-linear HDI + LG56 0.2 - 0.1 linear HDI+PEG200 0 — C\ Ο 0.2 0.4 0.6 0.8 1.0 Ρ Figure 1. Number of ring structure per molecule (N ) as a r function of extent of reaction(p) for linear and non-linear polyurethane forming reactions in bulk with approximately equimolar concentrations of reactive groups, r =[NCOl /[pHl S 1) (6,7). 0 0 0 - linear polymerisation, HDI + poly(ethylene glycol) (PEG200) at 70OC,[NCOj = 5.111 mol kg-1,[OH] = 5.188 mol 0 0 kg- ; number-average of bonds in chain forming smallest ring structure (v) = 25.2. • - non-linear polymerisation, HDI + POP triol (LG56) at 7QoC,[NCqIo = 0.9073 mol kg'SJ0Hj = 0.9173 mol kg-1; o v= 115. Reproduced with permission, from Ref. 2. Copyright 1982, American Chemical Society. In Characterization of Highly Cross-linked Polymers; Labana, S., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1984.
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