Thermo- and pH-responsive behaviors of graft copolymer and blend based on chitosan andN-isopropylacrylamide

Thermo- and pH-sensitive polymers were prepared by graft polymerization or blending of chitosan and poly(N-isopropylacrylamide) (PNIPAAm). The graft copolymer and blend were characterized by Fourier transform-infrared, thermogravimetric analysis, X-ray diffraction measurements, and solubility test. The maximum grafting (%) of chitosan-g-(N-isopropylacrylamide) (NIPAAm) was obtained at the 0.5 M NIPAAm monomer concentration, 2 × 10−3 M of ceric ammonium nitrate initiator and 2 h of reaction time at 25°C. The percentage of grafting (%) and the efficiency of grafting (%) gradually increased with the concentration of NIPAAm up to 0.5 M, and then decreased at above 0.5 M NIPAAm concentration due to the increase in the homopolymerization of NIPAAm. Both crosslinked chitosan-g-NIPAAm and chitosan/PNIPAAm blend reached an equilibrium state within 30 min. The equilibrium water content of all IPN samples dropped sharply at pH > 6 and temperature > 30°C. In the buffer solutions of various pH and temperature, the chitosan/PNIPAAm blend IPN has a somewhat higher swelling than that of the chitosan-g-NIPAAm IPN.