Volume Phase Transition in Interpenetrating Networks of Poly(N-isopropylacrylamide) with Gelatin

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.