Swelling Characteristics of Poly(N-isopropylmethacrylamide-co-itaconic acid) Gels Prepared in Various Conditions

Thermo- and pH-sensitive gels composed of N-isopropylmethacrylamide (NTPMA) and itaconic acid (IA) were prepared by free-radical crosslinking copolymerization in poly(ethylene glycol) (PEG) solution at 22 degrees C and in water at 22 degrees C and at 22 degrees C, which were called as the macroporous gel (MGel), the cryogel (CGel), and the conventional gel (NGel), respectively. The gels were characterized by the equilibrium swelling, interior morphology, and deswelling kinetics. With increasing temperature in water, the gels exhibit reentrant conformational phase transition. During this transition, the gels first deswell in the range of temperature between 5 and 29 degrees C, then drastically reswell if temperature is monotonically increased. The reswelling of the collapsed gels occurs above 45 degrees C. It was shown that the reentrant transition in poly(N-isopropylmethacrylamide-co-itaconic acid) [poly(NIPMA-co-IA)] gels requires moderate temperature, so that the hydrophobic interactions between chains dominate the swelling process. Scanning electron micrographs revealed that the interior network structure of MGel is more porous compared with those of CGel and NGel. This more porous structure provided numerous water channels for water diffusion out of the matrix and, therefore, an improved response rate to the external temperature and pH changes during the deswelling process. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 817-823, 2010