Microwave-Assisted Synthesis of a Brush-Like Copolymer of Poly(D,L-Lactide) Grafted onto Chitosan

Brush-like chitosan-g-poly(D,L-lactide) copolymers were synthesized effectively by bulk ring-opening polymerization of D,L-lactide(D,L-LA) using chitosan (CS) as macroinitiator under microwave irradiation. The graft copolymers were characterized by FT IR, ¹H NMR, EA, XRD, and TGA. The results showed that the synthesis of the chitosan-g-polylactide copolymer via microwave heating was much faster than via conventional heating. Compared with chitosan, the crystallinity and the thermal stability of graft copolymer decreased due to the intra/intermolecular hydrogen bonds existing in chitosan destroyed. The feeding molar ratio of D,L-lactide and chitosan(n_D,L-LA/n_CS) had a strong influence on the structure and properties of chitosan-g-poly(D,L-lactide) copolymer, in higher n_D,L-LA/n_CS feeding molar ratio led to copolymers with higher average degree of polymerization of polylactide branch chains, and the lower crystallinity and thermal stability.