Temperature/pH-sensitive comb-type graft hydrogels composed of chitosan and poly(N-isopropylacrylamide)

Comb-type graft hydrogels, composed of chitosan and poly(N-isopropylacrylamide) (PNIPAAm), were prepared to manifest rapid temperature and pH sensitivity. Instead of directly grafting the NIPAAm monomer onto the chitosan chain, semitelechelic PNIPAAm with carboxyl end group was synthesized by radical polymerization using 3-mercaptopropionic acid as the chain-transfer agent, and was grafted onto chitosan having amino groups. The comb-type hydrogels were prepared with two different graft yields and grafting regions, such as surface- and bulk-grafting, and then compared with a chitosan hydrogel. The synthesis of telechelic PNIPAAm and the formation of amide group were confirmed by using FTIR spectroscopy and gel permeation chromatography. Results from the water state and thermal stability revealed that the introduction of the PNIPAAm side chain disturbed the ordered arrangement of the chitosan molecule, resulting in an increase in the equilibrium water content. Comb-type graft hydrogels showed rapid temperature and pH sensitivity because of the free-ended PNIPAAm attached to the chitosan main chain and the chitosan amino group itself, respectively. In particular, the surface graft hydrogel maintained its dimension at low pH, although the chitosan main chain was not crosslinked, whereas chitosan and bulk graft hydrogel were dissolved as a result of the coating effect of pH-independent PNIPAAm. (C) 2004 Wiley Periodicals, Inc.