A strategy for in situ chemical gelation of poly(N-isopropylacrylamide-co-glycidyl methacrylate)/polyethylenimine (P(NIPAAm-co-GMA)/PEI) polymers has been demonstrated. Two kinds of P(NIPAAm-co-GMA) with epoxy pendant groups were prepared. When the solution of P(NIPAAm-co-GMA) was mixed with branched polyethylenimine (PEI, M(w) 800), the cross-linking between the epoxy functional groups and amines, a type of nucleophilic substitution reaction occurred. The corresponding gelation process was confirmed via theology. The in situ formed hydrogels were studied via scanning electric microscopy (SEM) and the equilibrium swelling ratio, swelling kinetics, and temperature response kinetics were examined. The strategy described here presents a potential alternative to the traditional synthesis techniques for the in situ formation of thermosensitive hydrogels. (c) 2008 Elsevier Ltd. All rights reserved.