110 Advancesin Polymer Science ResponsiveGels: Volume TransitionsII Editor: K. DuiIek With contributions by J.H. Burbau, E.L. Cussler, S.H. Gehrke, 0. Hiram, S. Hirotsu, M. Irie, E. Kokufi~ta, T. Okano, A. Suzuki, M. Suzuki, M. Tokita F?Verdugo, K.L. Wang With 144 Figures and 10 Tables Springer-Verlag Berlin HeidelbergNewYork London Paris Tokyo Hong Kong BarcelonaBudapest Volume Witor: Prof. K. DuSek Inst. of Macromolecular Chemistry Czech Academy of Sciences 162 06 Prague 6, Czech Republic ISBN 3-540-56970-7 Springer-Verlag Berlin Heidelberg NewYork ISBN o-387-56970-7 Springer-Verlag NewYork Berlin Heidelberg This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, m-use of illustrations, recitation, broadcasting, reproduction on microfilms or in other ways, and storage in data banks. Duplication of this publication or parts thereof is only permitted under the provisions of the German Copyright Law of September 9,1%5, in its current version, and a copyright fee must always be paid. Q Springer-Verlag Berlin Heidelberg 1993 Library of Congress Catalog Card Number 6 l-642 P&ted in Germany The use of registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names am exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: Macmillan India Ltd., Bangalore- Printing: salad~clc,Berlin; Bookbinding: LiIderitx & Bauer, Berlin 02/3020 543210 Printedonacid-freepaper Editors Prof. Akihiro Abe, Tokyo Institute of Technology, Faculty of Engineering, Department of Polymer Chemistry, 0-okayama, Meguro-ku, Tokyo 152, Japan Prof. Henri Benoit, CNRS, Centre de Recherches sur Ies Macromoldcules, 6, rue Boussingault, 67083 Strasbourg Cedex, France Prof. Hans-JoachimCantow, Institut ftir Makromolekulare Chemie der Universit& Stefan Meier-Str. 31, D-79194 Freiburg i. Br., FRG Prof. Paolo Corradini, Universiti di Napoli. Dipartimento di Chin&a, Via Mezzocannone 4, 80134 Napoli, Italy Prof. Karel DuSek,Institute of Macromolecular Chemistry, Czech Academy of Sciences, 16206 Prague 616, Czech Republic Prof. Sam Edwards, University of Cambridge, Department of Physics,Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, UK Prof. Hiishi Fujita, 35 Sbimotakedono-cho, Shichiku, Kita-ku, Kyoto 603 Japan Prof. Gottfried GMckner, Technische Universitit Dresden, Sektion Chemie, Mommsenstr. 13, D-01069 Dresden, FRG Prof. Dr. Hartwig H6cker. Lebrstuhl fir Textilchemie und Makromolekulare Chemie, RWTH Aachen, Veltmanplatz 8, D-52062 Aachen, FRG Prof. Hans-Heir&h H&hold, Friedrich-Schiller-Universittlt Jena, Institut ftir Grganische und Makromolekulare Chemie, Lehrstuhl OrganischePolymerchemie, Humboldtstr. 10, D-07743 Jena, FRG Prof. Hans-Henning Kausch,Laboratoire de Polymbres,Ecole PolytechniqueFed&ale de Lausanne, MX-D, CH-1015 Lausanne, Switzerland Prof. Joseph P. Kennedy, Institute of Polymer Science, The University of Akron, Akron, Ohio 44 325, USA Prof. Jack L. Koenig, Department of Macromolecular Science,Case Western Reserve University. School of Engineering, Cleveland, OH 44106, USA Prof. Anthony Ledwith. Pilkington Brothers plc. R & D Laboratories, Lathom Ormskirk, Lancashire L40 SUF, UK Prof. J. E. McGrath, Polymer Materials and Interfaces Laboratory, Virginia Polytechnic and State University Blacksburg, Virginia 24061, USA Prof. Lucien Monnerie, Ecole Superieurede Physiqueet de Chimie Industrielles, Laboratoire de Physico-Chimie, Structurale et MacromolBculaire 10, rue Vauquelin, 75231 Paris Cedex 05, France Prof. Seizo Okamura, No. 24, Minamigoshi-Machi Okazaki, Sakyo-Ku, Kyoto 606, Japan Prof. Charles G. Overberger, Department of Chemistry, The University of Michigan, Ann Arbor, Michigan 48109, USA Prof. Helmut Ringsdorf, Institut fth Grganische Chemie. Johannes-Gutenberg-Universititt, J.-J.-Becher Weg 18-20, D-55128 Mainz, FRG Prof. Takeo Saegusa,KRI International, Inc. Kyoto ResearchPark 17, Chudoji Minamima- chi, Shimogyo-ku Kyoto 600 Japan Prof. J. C. Salamone, University of Lowell, Department of Chemistry, College of Pure and Applied Science, One University Avenue, Lowell, MA 01854, USA Prof. John L. Schrag,University of Wisconsin, Department of Chemistry, 1101 University Avenue. Madison, Wisconsin 53706, USA Prof. G. Wegner, Max-Planck-lnstitut ftlr Polymerforschung,Ackermannweg 10, Postfach 3148, D-55128 Mainz, FRG Preface Gels are cross-linked networks of polymers swollen with a liquid. Softness, elasticity, and the capacity to store a fluid make gels unique materials. As our society becomes richer and more sophisticated, and as we increasingly recognize that natural resources are not unlimited, materials with better quality and higher functional performance become more wanted and necessary. Soft and gentle materials are beginning to replace some of the hard :mechanical materials in various industries. Recent progress in biology and polymer sciences is unveiling the mystery of marvellous functions of biological molecules and promises new development in gel technologies. All these factors bring us to realize the importance and urgent need of establishing gel sciences and technologies. Due to the cross-linking, various properties of individual polymers become visible on a macroscopic scale. The phase transition of gels is one of the most fascinating and important phenomena that allows us to explore the principles underlying the molecular interactions and recognition which exist in synthetic and biological polymers. The polymer network changes its volume in response to a change in environment; temperature, solvent composition, mechanical strain, electric field, exposure to light, etc. The prediction and finding of the phenomenon have opened the door to a wide variety of technological appli- cations in chemical, medical, agricultural, electrical, and many other industrial fields. The volume phase transition in gels has its history. It was theoretically predicted before it was discovered experimentally. However, the path from theory to experiment was not so straighforward because the conclusion of the theoretical analysis was that conditions for such a transition could hardly be met experimentally. Among the participants of the IUPAC International Symposium on Macromolecular Chemistry in Prague in 1965, were the Editor of this volume (K.D.) and Donald Patterson (D.P.) of the CRM in Strasbourg and later McGill University in Montreal. D.P., well-known for his work in polymer solutions thermodynamics, presented a paper in this area, and K.D. presented a theor- etical paper on phase separation in gels. This, however, concerned separation of a liquid from a swollen gel as a result of deterioration of polymer-solvent interaction or increasing crosslinking density during the crosslinking process where dilutions during crosslinking played an important role [1]. At the time of the conference, D.P. and K.D. discussed the possible peculiar shapes of the solvent chemical potential vs composition curves in swollen vi Preface polymer networks prepared at different dilutions during network formation and values of the polymer solvent interaction parameter. Some of these curves exhibited a minimum followed by a maximum, a condition necessary for coexistence between two phases of different composition. Also at this sym- posium, a paper was given by Oleg Ptitsyn [2] on globule--coil transition in which he showed that a polyelectrolyte chain can undergo a collapse transition if the polymer-solvent interaction or degree of ionization were changed. All this inspired us in a deeper investigation of the phase equilibria in swollen polymer networks. The result of analysis showed that a thermodynamic transition between two gels states differing in polymer concentration can be real and that the transition can be brought about not only by a change in the interaction parameter (temperature) but also by deformation. To exhibit this phase transition, the gel was to be prepared in the presence of a sufficient amount of diluent, its crosslinking density had to be sufficiently high, and the solvent in which it was swollen had to be rather poorer. The mechanistic explanation of the predicted phase transition was as follows: the network chains, after removal of the diluent after crosslinking, were rather supercoiled and had a tendency to assume more relaxed (expanded) conformation; this tendency was resisted by a strong ten- dency towards polymer segment association due to an unfavorable polymer - solvent interaction (poor solvent). The balance between these two strong and oppositely acting forces gave rise to the possibility of phase transition. However, it had turned out that preparation of such non-ionic gets at a high content of diluent and having high crosslinking density would be difficult due to a danger of gel-liquid phase separation during preparation. It was clear that a strong concentration dependence of the polymer solvent interaction parameter of the swelling liquid would greatly facilitate the occurrence of phase transition. Polyelectrolyte gels were not considered at all, although they could have been theoretically analyzed in view of the Ptitsyn's prediction of the globule-coil transitions. The first report on the gel-gel transition was presented in September 1967 at the 1st Prague Microsymposium on Marcomolecules [3]. A paper was sub- mitted to the Journal of Polymer Science and was published in 1968 [4]. One of the referees wrote