Chitosan/oligo L-lactide graft copolymers: Effect of hydrophobic side chains on the physico-chemical properties and biodegradability

Graft copolymerization of L-lactide (LLA) onto chitosan (CS) was carried out by ring opening polymerisation using Ti(OBu)4 as catalyst in DMSO at 90 °C in nitrogen atmosphere to obtain chitosan/oligo L-lactide graft copolymers (CL). The ring opening polymerisation of L-lactide using a covalent initiator would significantly reduce the risk of racemization even at high temperatures in comparison to other polymerization methods. It is also expected to provide copolymers having better physico-chemical properties and biodegradability than the homopolymers for applications in biomedical and pharmaceutical fields. Grafting studies indicated that the lactide content in the feed molar ratio influenced the grafting percentage and the amount of lactide in the graft copolymer. The graft copolymers were characterized by FTIR, 1H NMR, WAXD and thermal methods. Unlike chitosan, all CL graft copolymers were converted to hydrogels in aqueous environment. As expected, the swelling ratio was found to be decreasing on increasing the amount of hydrophobic side chains in the graft copolymers. Similarly, the LLA content of the graft copolymers was found to influence their biodegradation carried out in vitro by hydrolytic and enzymatic means. DSC analysis and SEM micrographs of the hydrolytically degraded samples showed variations in degradation depending on the amount of LLA content. Enzymatic degradation was studied by exposing the samples to two types of enzymes such as papain from Carica Papaya and lipase from Candida Cylindracea. Examinations by SEM, weight loss studies, FTIR and DSC analysis showed that the biodegradation of the graft copolymers could be controlled by the LLA content. In conclusion, the grafting of LLA onto CS results in CL graft copolymers having increased hydrophilicity and controlled degradation rate that may have wide applications in wound dressing and in controlled drug delivery systems.