Heterogeneous Radioinduced Graft Copolymerization of Caprolactone in Nanochitosan

Abstract

This work focus on the chitosan-caprolactone graft copolymers’ (Ch-g-CL) synthesis through Radio Induced Grafting (RIG) of heterogeneous blends of solid chitosan polymers (particulated and nanoprecipitated) and liquid ε-caprolactone monomer, without the need of further reagents nor dissolution. The irradiation process was conducted at room temperature with gamma radiation from 60Co, followed in air and also under vacuum. Commonly applied sterilization doses of 25 and 45 kGy were used. The samples were analyzed, before and after irradiation, through FTIR-ATR, elemental analysis, scanning electron microscopy, 1H-NMR and size exclusion chromatography (SEC). It was found that copolymerization was successful on the blends with nanochitosan, due to a drastic increase in the active surface of the biopolymer. It was observed that the incorporation was better at higher doses and while irradiated on air, with up to 29% caprolactone incorporation. FTIR studies, along with elemental analysis and SEC, indicate that the most probable reaction is caprolactone grafting from/onto chitosan's amine groups. It was also observed that the incorporation increased in the higher molecular weight chitosan, which also has higher amine content. Practically, copolymers with 5–10% grafting sites with CL side chains of up to nine units, were obtained depending on the case. These RIG syntheses showed to lead to tunable Ch-g-CL structures of interest for biomedical applications as tissue scaffolds and drug delivery systems.