Semi-interpenetrating network (semi-IPN) polymer gels and interpenetrating network (IPN) polymer gels with thermosensitivity were prepared by introducing a biodegradable polymer, chitosan, into the N-isopropyacrylamide (PNIPAAm) gel system. The swelling behavior, temperature sensitivity, pH sensitivity, gel strength, and drug-release behavior of PNIPAAm/chitosan semi-IPN and IPN hydrogels were investigated. The results indicated that the NIPAAm/chitosan semi-IPN and IPN hydrogels exhibited pH and temperature-sensitivity behavior and could slow drug release and diffusion from the gels. From the stress-strain curves of the hydrogels, the compression moduli of IPN gels containing crosslinked chitosan were higher than those of semi-IPN gels. This is because IPN gels have a more compact structure. The morphology of PNIPAAm/chitosan hydrogels was also investigated.

Graft polymerization of N-isopropylacrylamide (NIPAAm) onto styrenebutadiene-styrene (SBS) block copolymer using benzoyl peroxide was studied to improve the water absorptivity and thermosensitivity of SBS. The influence of various grafting reaction factors on the conversion of NIPAAm and the grafting percentage of SBS-g-NIPAAm were also investigated in the study. The experimental results showed that the conversion of SBS-g-NIPAAm was enhanced as the monomers of NIPAAm were increased. The maximum conversion of SBS-g-NIPAAm was observed when the molar ratio of NIPAAm to butadiene was 1.25. In addition, increasing the reaction time enhanced the conversion of SBS-g-NIPAAm; the maximum grafting percentage was obtained with a 4-h reaction. The optimal concentration of the initiator was 3 ϫ 10 Ϫ4 mol/20 mL of toluene, and the grafting reaction occurred at over 65°C. The test results of the hydrophilicity of the grafted membranes showed that the hydrophilicity and thermosensitivity were significantly enhanced by grafting NIPAAm onto SBS.