A temperature- and pH-sensitive poly(N,N-diethylacrylamide-co-methacrylic acid) hydrogel with expanded conformations was synthesized in an alkaline solution of Tris-HCl buffer solution at pH 9.48. The deswelling dynamics of hydrogels and scanning electron microscopy micrographs revealed that the unique properties achieved were attributable to the expanded conformations generated in the alkaline solution during the copolymerization reaction. As a result of the dissociation of the carboxyl groups of MAA to carboxylate anions, the electrostatic repulsion between carboxylate anions was strong to lead to expanded conformations of polymer chains. Therefore, the network of the hydrogels thus obtained was extremely expanded to exhibit fast temperature sensitivity.

Key words: temperature- and pH-sensitivity, hydrogel, deswelling dynamics, expanded conformation, scanning electron microscopy