Preparation and characterization of UV-sensitive chitosan for UV-cure with poly(ethylene glycol) dimethacrylate

In this study, gel membranes of chitosan-g-poly(ethylene glycol) dimethacrylate (CS-g-PEGDMA) with pH sensitive properties were synthesized without employing any photo-initiator and crosslinker. First, CS was endowed with UV-sensitive property by reaction with cinnamoyl chloride in methanesulfonic acid. The reaction mainly occurred on the hydroxyl groups of the pyranose unit, while most C-2 amino groups were protected. The substitution degree of cinnamoyl group was 0.98, while the protection efficiency of –NH2 was about 80 %. Upon UV-irradiation, initial free radicals were produced only along the cinnamoyl-modified CS chains, which induced the grafting of PEGDMA from the chitosan chains and eventually the crosslinking. Increasing the feeding amount of PEGDMA increased the grafting ratio as well as the crosslinking density. The Tg value decreased from 161 °C for the pure chitosan to about 90 °C for the CS-g-PEGDMA with a grafting ratio of 1.29. Two stages of degradation correspondent to the individual degradation of CS chains and the PEGDMA chains were observed for all CS-g-PEGDMA copolymers, demonstrating their nature of graft copolymers. The tensile mechanical properties of the CS-g-PEGDMA membranes were affected by the two opposing factors: inter-connected soft PEGDMA chains and crosslinking density; and the optimum properties were achieved when the grafting ratio was increased to about 0.80. By combining CS and PEGDMA components, these copolymer membranes thus have the potential to be used as biomedical membranes.