Thermoresponsive hydrogels based on N-isopropylacrylamide and N-vinylimidazole were synthesized, and their swelling-deswelling behavior was studied as a function of the total monomer concentration. For copolymeric structures with better thermoresponsive properties with respect to poly(N-isopropylacrylamide-co-N-vinylimidazole) hydrogels, these hydrogels were protonated with HCl and HNO3, and the copolymer behaviors were compared with those of the unprotonated hydrogels. The temperature was changed from 4 to 70degreesC at fixed pHs and total ionic strengths. The equilibrium swelling ratio, dynamic swelling ratio, and dynamic deswelling ratio were evaluated for all the hydrogels. (C) 2004 Wiley Periodicals, Inc.