Thermoreversible hydrogels XIV. Synthesis and swelling behavior of the (N-isopropylacrylamide-co-2-hydroxyethyl methacrylate) copolymeric hydrogels

A series of thermoreversible hydrogels were prepared from various molar ratios of N-isopropylacrylamide (NIPAAm), and 2-hydroxyethyl methacrylate (HEMA) with N,N-methylene-bis-acrylamide (NMBA) as a crosslinker in various polymerization media. The appearance of the gel membrane formed in various polymerization media, and the influences of various swelling media on the swelling behavior for the copolymeric gels, were investigated in this article. The results indicated that the gel would change from opaque to transparent, and the swelling diffusion mechanism of the gel in water was changed from non-Fickian diffusion to Fickian diffusion when the content of HEMA in the copolymeric compositions increased. The effect of the swelling media on the swelling ratio for poly(NIPAAm-co-HEMA) indicated that the more the HEMA content, the lower the swelling ratio of the gel in water and solvent, but the contrary result for the gel was obtained in the 50% solvent aqueous solution. The result for the influence of the polymerization media on the swelling ratio for poly(NIPAAm-co-HEMA) indicated that the larger the solvent molecular size of polymerization media, the higher the swelling ratio. On the other hand, the gel transition temperature and the thermoreversibility of the copolymeric gels gradually disappeared as the content of the HEMA in the gel was increased. The larger the solvent molecular sizes of polymerization media, the better the thermoreversibility of the gel, but the gel transition temperature was not significantly affected. Finally, the drug release and drug diffusion in these copolymeric gels was also investigated.