Synthesis and characterization of novel pH-sensitive chitosan-poly(acrylamide-co-itaconic acid) hydrogels

Novel pH-sensitive chitosan-poly(acrylamide-co-itaconic acid) hydrogels were prepared by free radical copolymerization of acrylamide and itaconic acid (IA) in chitosan solution. The hydrogels were characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, differential scanning calorimetry and the swelling ratios of the hydrogels in water (pH 6.8) and pH 1.2. The influence of composition on the thermal properties of the hydrogels was assessed. The glass transition temperatures of the samples increased with IA content, ranging from 110 to 136 degrees C. Swelling of the hydrogels was found to obey second-order kinetics with respect to the remnant swelling, indicating that diffusion is controlled by the relaxation of chains. The equilibrium swelling degree was strongly dependent on pH and composition. At both pH values the highest water uptake was obtained for the IA-free sample M1. From the equilibrium swelling results the average molar mass between crosslinks, M-c, and the crosslink density of the chitosan-poly(acrylamide-co-itaconic acid) samples were calculated. The results evidenced the reinforcing effect of IA on the hydrogel structure. It is concluded that these highly swellable pH-sensitive hydrogels can be useful for applications in biomedicine and pharmacy. (C) 2014 Society of Chemical Industry