Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(N-isopropylacrylamide) (PNIPAAm) were prepared by the sequential-IPN method. The characterizations of IPN hydrogels were investigated by swelling experiment, Fourier transform infrared (FT-IR) spectroscopy and differential scanning calorimetry (DSC). IPN hydrogels exhibited a relatively high swelling ratio in the range 180-300% at 35 degreesC. The swelling ratio of hydrogels depended on pH and temperature. DSC was used for the quantitative determination of the amounts of freezing and non-freezing water. Free water contents in the hydrogels IPN1, IPN2 and IPN3 were 45.8, 37.9 and 33.1% in pure water, respectively. (C) 2002 Elsevier Science B.V. All rights reserved.