Abstract

Hydrogels have been synthesized by free radical co-polymerization of acrylamide and maleic acid in the presence of poly(N-vinyl-2-pyrrolidone) in aqueous medium. The presence of a small amount of maleic acid in the polymer network increased the swelling capacity appreciably, thus changing the Fickian swelling behavior to a non-Fickian one. The hydrogels showed good response to pH, ionic-strength and valency of counterions in the external media. The hydrogels demonstrated minimum swelling in the strongly acidic range 1–2 and maximum swelling was observed in the neutral or slightly alkaline medium (7–8). The amount of maleic acid in the hydrogel affected its swelling behavour in a rather unusual way. At pH 7.0, the equilibrium swelling increased up to 123 mM of maleic acid in the system and then started decreasing, while at a low pH, a continuous decrease was observed. The hydrogels underwent a number of deswelling swelling cycles with a pH change from 1.0 to 8.0, respectively. The hydrogels demonstrated temperature-dependent swelling behavior partially, and activation every for the sample with and without maleic acid was found to be 33.1 and 19.9 kJ mol−1. Finally, the pH - dependent swelling behavior makes them suitable for a drug delivery device along the gastrointestinal (GI) tract.