Thermoresponsive Super Water Absorbent Hydrogels Prepared by Frontal Polymerization of N-Isopropyl Acrylamide and 3-Sulfopropyl Acrylate Potassium Salt

Super water absorbent polymer hydrogels were synthesized by frontal polymerization. These materials were obtained by copolymerizing N-isopropyl acrylamide (NIPAAm) and 3-sulfopropyl acrylate potassium salt (SPAK) in the presence of N,N-methylene-bis-acrylamide as a crosslinker. It was found that their swelling behavior in water can be easily tuned by using either the appropriate monomer ratio or the amount of the crosslinker used. Namely, the swelling ratio was found to range from about 1000% for the NIPAAm homopolymer in the presence of 5.0 mol % of crosslinker, up to 35,000% for the sample containing 87.5 mol % of SPAK and 1.0 mol % of crosslinker. The affinity toward water was also confirmed by contact angle analysis. Moreover, the obtained hydrogels exhibit a thermoresponsive behavior, with a lower critical solution temperature of about 28-30 degrees C. This value is close to that of poly(NIPAAm) but with a swelling capability that dramatically increases as the amount of SPAK increases. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1228-1234, 2011