Kinetics of the volume phase transition in poly(n‐isopropylacrylamide) gels prepared under high pressure

Abstract

New poly(N-isopropylacrylamide) gels were prepared under high pressure (ca. 200 MPa) during gelation. The preparation-pressure dependence of the deswelling speed of the gels was measured with a conventional T-jump method. The deswelling time of a gel rod 2.2 mm in diameter prepared at 193 MPa was about 200 s, 1000 times faster than that of a homogeneous poly(N-isopropylacrylamide) gel. Moreover, the collective diffusion coefficient, the thermal fluctuation, and the ensemble-average intensity of the swollen gel networks were obtained with dynamic light scattering measurements. Both the enthalpy and entropy of the gels were estimated from equilibrium swelling curves with the Flory–Huggins interaction parameter evaluated with mean field theory based on the Flory-type of the Gibbs free-energy formula. It was found that the networks of the gels had an inhomogeneous structure newly introduced by the preparation pressure. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2315–2325, 2001