Novel Redox Hydrogel by in Situ Gelation of Chitosan as a Result of Template Oxidative Polymerization of Hydroquinone

Abstract

A new redox hydrogel using poly(hydroquinone) (PHQ) as polymeric redox couple and chitosan as matrix was synthesized by simple exposing an acidic chitosan/hydroquinone (HQ) solution to the air. PHQ was synthesized in situ by oxidative polymerization of HQ using oxygen as an oxidant. The presence of chitosan increases the reaction rate significantly, suggesting chitosan works as a template for the polymerization of HQ. The reaction rate increases linearly with chitosan concentration when molar ratio of chitosan/HQ is less than 0.96 but keeps constant beyond that point. These results suggest a pick-up mechanism for the template polymerization of HQ. The polymerization of HQ further results in the gelation of the aqueous solution, as physical cross-links forms between PHQ and chitosan. The gelation time decreases with increasing chitosan and HQ concentration and also increasing temperature. The resultant hydrogel are redox-active. Cyclic voltammogram of the hydrogel presents two oxidation peaks at 0.62 and 1.23 V and two reduction peaks at −0.79 and −1.66 V (vs Ag/AgCl). The in situ-formed redox hydrogel may find applications in biomedical areas.