EFFECT OF CROSSLINKING ON SWELLING, TRANSITIONS AND MECHANICAL PROPERTIES OF POLY(N-ISOPROPYLACRYLAMIDE) RESPONSIVE HYDROGELS

摘要

N-isopropylacrylamide (NIPA) was copolymerized with different concentrations of N, N'-methylenebisacrylamide (MBA) to obtain networks of different crosslinking densities. Semiinterpenetrating networks of the same crosslinking densities were obtained by copolymerization of NIPA and MBA in the presence of linear polyacrylamide (5 wt.%). The equilibrium swelling degree in water at 25°C varied from 7.61 to 16.8 times the original volume when the molar ratio NIPA/MBA increased from 10:1 to 100:1. The transition temperature determined by DSC was largely unaffected by the crosslinking conditions in this work. Crosslinking density obtained from dynamic shear measurements was much lower than predicted from the molar ratio of the monomer and crosslinker, which was explained by the incomplete reaction. The sol fraction varied from 12% to 30%. Thermomechanical analysis showed contraction followed by the expansion of the gels during transition. The broadening of the temperature range of the gel collapse was observed as the crosslinking density increased. Tensile strength of the 10% swollen Semiinterpenetrating NIPA networks was higher. (15-23 kPa) than that of the 10% swollen single NIPA networks (9-13 kPa). Elongations at break were significantly higher for semi IPN gels compared to the single ones, especially at lower crosslinking densities.