Synthesis and thermo-responsive properties of chitosan-g-poly (N-isopropylacrylamide) and HTCC-g-poly(N-isopropylacrylamide) copolymers

Carboxyl group-terminated poly(N-isopropylacrylamide) (PNIA-COOH) was synthesized via radical polymerization of N-isopropylacrylamide (NIA) using mercaptoacetic acid (MAA) as a chain transfer agent. The molecular weight of the PNIA-COOH was controlled by changing the molar ratio of MAA to NIA. A water-soluble chitosan derivative, N-(2-hydroxy)propyl-3-trimethylammonium chitosan chloride (HTCC), was also synthesized by reacting chitosan with glycidyltrimethylammonium chloride. Then, chitosan-g-PNIA and HTCC-g-PNIA copolymers were synthesized using the “graft-onto” method by reacting PNIA-COOH with chitosan and HTCC, respectively. The formation of the grafted copolymers was confirmed by Fourier transform infrared spectroscopy, solubility test in water, and scanning electron microscopy — energy dispersive spectroscopy. The thermo-responsive behaviors of the grafted copolymers and the change in lower critical solution temperature (LCST) were also studied. Chitosan-g-PNIA was insoluble in water and behaved like a thermo-responsive hydrogel due to the crosslinking-point action of the chitosan backbone. The swelling ratio of chitosan-g-PNIA increased with increasing PNIA content. HTCC-g-PNIA behaved as a water-soluble thermo-responsive polymer. Compared to the homo PNIA, the LCST of HTCC-g-PNIA was slightly increased.