Poly(N-isopropylacrylamide) (PNIPAAm)/poly(ethylene oxide) (PEO) semi-interpenetrating polymer networks (semi-IPNs) synthesized by radical polymerization of N-isopropylacrylamide (NIPAAm) in the presence of PEO. The thermal characterizations of the semi-IPNs were investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and dielectric analysis (DEA). The melting temperature (T-m) of semi-IPNs appeared at around 60degreesC using DSC. DEA was employed to ascertain the glass transition temperature (T-g) and determine the activation energy (E.) of semi-IPNs. From the results of DEA, semi-IPNs exhibited one T-g indicating the presence of phase separation in the semi-IPN, and T(g)s of semi-IPNs were observed with increasing PNIPAAm content. The thermal decomposition of semi-IPNa was investigated using TGA and appeared at around 370degreesC. (C) 2003 Wiley Periodicals, Inc.