Swellable polymers functionalized to respond to pH have been prepared from microgels of poly (N-isopropylacrylamide) copolymerized with acrylic acid, methacrylic acid, ethacrylic acid and propacrylic acid. When these N-isopropylacrylamide polymer particles are dispersed in a hydrogel, large changes occur in the turbidity of the membrane (measured by an absorbance spectrometer) as the pH of the solution in contact with the membrane is varied. Changes of approximately 0.3 absorbance units were observed in the swelling and shrinking of these pH sensitive copolymers of N-isopropylacrylamide. Swelling was nonionic as the ionic strength of the solution in contact with the copolymers was increased from 0.1M and 1.0M without a concomitant decrease in swelling. For many of the copolymers, swelling was also reversible in both low and high ionic strength pH buffered media at both ambient and physiological temperatures. Changes in the composition of the formulation used to prepare these copolymers could be correlated to their response to changes in the pH of the buffer solution in contact with them.Chemistr
