Swelling Behavior of Stimuli-Sensitive Hydrogels Based on N-Isopropylacrylamide and Sodium Acrylate Copolymer

Stimuli-sensitive poly (N-isopropylacrylamide-co-sodium acrylate) [poly (NiPAAm-co-SA)] hydrogels are prepared by free radical polymerization of N-isopropylacrylamide (NiPAAm) and sodium acrylate (SA) using N, N'-methylene bisacrylamide (BIS) as a crosslinking agent. The effects of SA content, crosslinking agent concentration and the pre-gel solution concentration on the swelling behavior of poly (NiPAAm-co-SA) hydrogel are investigated systematically. The results indicate that the swelling capacities increase with an increase in the amount of hydrophilic poly (sodium acrylate) anionic units, and thermo-sensitivity is weakened simultaneously. The effect of the pre-gel solution concentration on the swellabilities of poly (NiPAAm-co-SA) is more than that of the crosslinking agent concentration. Furthermore, the pH-sensitivity of the networks is also investigated, and it is found that the swelling behavior of poly (NiPAAm-co-SA) hydrogels obviously improves when the pH value is 5.