Temperature-sensitive poly(N-isopropylacrylamide) hydrogels were successfully synthesized by using poly(ethylene oxide) as the interpenetrating agent. The newly prepared semi-interpenetrating polymer network (semi-IPN) hydrogels exhibited much better properties as temperature-sensitive polymers than they did in the past. Characterizations of the IPN hydrogels were investigated using a swelling experiment, FTIR spectroscopy, and differential scanning calorimetry (DSC). Semi-IPN hydrogels exhibited a relatively high temperature dependent swelling ratio in the range of 23-28 at room temperature. DSC was used for the determination of the lower critical solution temperature of the semi-IPN hydrogel. (C) 2003 Wiley Periodicals, Inc.