Interpenetrating polymer network (IPN) hydrogels based on poly(ethylene oxide) and poly(methyl methacrylate) were prepared by radical polymerization using 2,2-dimethyl-2-phenylacetophenone and ethylene glycol dimethacrylate as initiators and crosslinkers, respectively. The IPN hydrogels were analyzed for sorption behavior at 25degreesC and at a relative humidity of 95% using dynamic vapor sorption. The IPN hydrogels; exhibited a relatively high equilibrium water content in the range of 13-68%. The state of water in the swollen IPN hydrogels was investigated using differential scanning calorimetry. The free water in the hydrogels increased as the hydrophilic content increased. (C) 2003 Wiley Periodicals, Inc.