Preparation of Fast-Response pH-Sensitive PNIPAAm- co-PAAc Hydrogels and Their Swelling Kinetics

A series of porous PNIPAAm-co-PAAc hydrogels were synthesized by radical copolymerization of (N-isopropylacrylamide)(NIPAAm) and acrylic acid(AAc) using silica particles as a porogent. The dynamic swelling kinetics of the hydrogels pretreated in different buffer solutions have been studied. Experimental results revealed that the swelling rate of the porous hydrogels greatly increased in comparison with nonporous hydrogels due to their porous structure. And although the previous treatment did not affect the equilibrium swelling (degree) of (copolymer) hydrogels, a strong influence on their dynamic swelling kinetics was still observed (especially) for the copolymers with composition of NIPAAm between 30% and 70%(mole fraction). When subsequently soaked in a neutral (solution) with pH=7, these copolymer samples exhibited sigmoidal swelling curves by an autoacceleration mechanism. The dynamic swelling of the copolymer and homopolymer hydrogels at pH=7 after soaking in a solution of the same pH can be described by second-order kinetics.