Poly(ethylene glycol)s (PEGs) in the molecular weight range 200−3400 were derivatized at both ends with acryloyl chloride. These poly(ethylene glycol) diacrylates (PEGDAs) on homopolymerization yield cross-linked networks whose M c values should correspond to the molecular weight of the PEGDA macromer. M c values calculated according to the Flory−Rehner equation compare very well with the theoretical values for low concentrations of low molecular weight monomers. Those at high concentrations and higher molecular weights are always lower than the expected values. Attempts to resolve the equilibrium swelling and elastic components indicate that the phantom model gives a better fit.

A series of interpenetrating polymer networks (IPNs) of poly(N‐isopropylacrylamide) (PNIPA) with anionic poly(acrylic acid) (PAA) and cationic poly[[3‐(methacryloylamino)propyl]trimethylammonium chloride] (PMAPTAC) have been synthesized. The swelling behavior of the IPNs is monitored as a function of both pH and temperature. The swelling ratios of IPNs are significantly larger than those reported for pure PNIPA gels. [PNIPA‐PAA] IPNs show a continuous volume phase transition (VPT) at pHs below the pKa of PAA and at pH > pKa the IPNs show a temperature independent swelling. [PNIPA‐PMAPTAC] IPNs do not exhibit VPT at any given pH and over the range of temperatures studied.

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Fully interpenetrating polymer networks (IPNs) of gelatin and poly(N-isopropylacrylamide) (PNIPA) are synthesized. The IPNs exhibit volume phase transition in aqueous medium and re-entrant type behavior in mixed solvent systems similar to pure PNIPA hydrogels. Neither the hydrophilic ambience of the gelatin network nor the additional topological constraints imposed by the IPN morphology restrain the characteristic features of PNIPA suggesting short-range interactions are responsible for the volume phase transition (VPT) phenomenon. Thus it could very well be that the conditions of the planarity of the amide group together with the directionality of the H bonds with the solvent decide the phenomenon of lower critical solution temperature (LCST)/VPT in PNIPA polymers.