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Tanaka F.,Institute of Theoretical Polymer Science | Katsumoto Y.,Hiroshima University | Nakano S.,Tokai University | Kita R.,Tokai University
Reactive and Functional Polymers | Year: 2013

Stereoregular poly(N-isopropylacrylamide)s with controlled content of isotactic dyads have recently been synthesized, and interesting interference phenomena between LCST phase separation and high-temperature reversible gelation have been observed in their aqueous solutions. We develop a model solution in which dehydrated stereo-regular isotactic segments on polymers are driven into intermolecular cross-links leading to gelation. We theoretically calculate the phase diagrams for the varied content isotactic dyads and compare with the experimental data. © 2013 Elsevier Ltd. All rights reserved.

Kojima H.,Kyoto University | Tanaka F.,Kyoto University | Tanaka F.,Institute of Theoretical Polymer Science | Scherzinger C.,RWTH Aachen | Richtering W.,RWTH Aachen
Journal of Polymer Science, Part B: Polymer Physics | Year: 2013

Temperature dependent phase behavior of poly(N-isopropylacylamide) (PNIPAM) microgels in water/methanol mixtures of different composition was studied with dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Using DLS, it is possible to measure the diffusion coefficient, and thus the size of particles exactly and directly; the variation of the phase transition temperature in the different solvents is also easy to detect by this method. With SANS measurements in D2O/MeOD mixtures, some of the DLS results were confirmed. Moreover, SANS measurements give valuable information on the particle structure in different solvents. The experiments were compared with the theory of competitive hydration introduced by Tanaka et al. We found a good agreement of theory and experiment, and obtained the theoretical predictions: around the transition temperature, the composition of the bound methanol along the chains is higher than that of the outer solution, while the whole methanol composition inside the gel is lower. © 2013 Wiley Periodicals, Inc.

Kojima H.,Kyoto University | Tanaka F.,Institute of Theoretical Polymer Science
Journal of Polymer Science, Part B: Polymer Physics | Year: 2013

We develop a theoretical model of cooperative hydration to clarify the molecular origin of the observed nonlinear depression of the lower critical solution temperature (LCST) in the aqueous solutions of thermosensitive random copolymers and find the monomer composition at which LCST shows a minimum. Phase diagrams of poly(N-isopropylacrylamide-co-N,N-diethylacrylamide) copolymer solutions are theoretically derived on the basis of the theory of cooperative hydration by introducing the microscopic structure parameter η which characterizes the distribution of the monomer sequences along the chains. We compared them with the experimental data of LCST of random copolymers with various monomer compositions and also of the diblock copolymers with equimolar monomer composition. The transition temperature shifts to lower than those of homopolymer counterparts when the monomer sequence of the chains has an alternative tendency. On the contrary, for the blocky polymers such as diblock copolymers, the transition temperature remains almost the same as those of the homopolymers. Thus, the nonlinear effect in phase separation appears when the average block length of the copolymers is shorter than the average sequence length of the cooperative hydration. The degree of hydration is calculated as a function of the temperature and polymer concentration for varied distribution of the copolymer compositions. © 2013 Wiley Periodicals, Inc.

Tanaka F.,Institute of Theoretical Polymer Science
Nihon Reoroji Gakkaishi | Year: 2013

A new transient network model of telechelic associating polymers whose main chains undergo sharp temperatureresponsive coil-globule transition is developed for the study of the rheological properties near their collapse transition point. It is shown that the two fundamental relaxation times, the time scale of the conformational change and the time scale of the end-chain dissociation, compete. As a result of their coupling, two distinct slow-and fast relaxation modes appear. The complex modulus is calculated and shown to take the form of the Burgers model made up of a Maxwell and a Voigt element connected in series. In the limit of high reaction rate of the conformation change, the slow mode reduces to the average relaxation time of the end-chain dissociation, while the fast mode disappears. The two relaxation times and the plateau modulus are obtained in terms of the molecular parameters of the telechelic polymer. Possible comparison with the recent experimental data on telechelic poly(N-isopropylacrylamide) networks in water is suggested. © 2013 The Society of Rheology, Japan.

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