SWELLING EQUILIBRIA FOR WEAKLY IONIZABLE, TEMPERATURE-SENSITIVE HYDROGELS

Swelling equilibria in aqueous citrate-phosphate buffer solutions are reported for thermally sensitive poly(N-isopropylacrylamide) hydrogels containing weakly ionizable groups. The comonomers containing these groups were sodium acrylate and 2-(dimethylamino)ethyl methacrylate to produce gels with, respectively, acidic and basic character. Gel swelling was measured as a function of pH, ionic strength, and temperature. With increasing ionization, the temperature range over which the gel volume change is greatest becomes larger and shifts to higher temperatures.