Rapid synthesis and characterization of chitosan-g-poly(D,L-lactide) copolymers with hydroxyethyl chitosan as a macroinitiator under microwave irradiation

Hydroxyethyl chitosan (HECS) was first prepared by the reaction of 2-chloroethanol with chitosan (CS). Then, CS-g-poly(D,L-lactide) (PDLLA) copolymers were synthesized through the ring-opening polymerization of D,L-lactide with CS and HECS as the macroinitiators, respectively, under microwave irradiation. The optimal synthesis conditions obtained by an orthogonal experiment were as follows: microwave power = 10 W, temperature = 130 degrees C, irradiation time = 15 min, and catalyst concentration = 0.05 mol %. The reactivity of CS was improved by hydroxyethylation, which contributed to a higher percentage of grafting. Compared with the conventional thermal polymerization, the microwave polymerization method showed a significantly higher polymerization rate and improved efficiency. An enhanced percentage of grafting ranging from 236.25 to 317.50%, and an average degree of polymerization of PDLLA side chains ranging from 13.25 to 24.17 were achieved under microwave irradiation when the value of nD,L-lactide/nminoglucoside units was increased from 20 : 1 to 40 : 1. The higher percentage of grafting facilitated decreases in the crystallinity and thermal stability of the copolymers, which were attributed to the weakening intramolecular and intermolecular hydrogen bonds of CS. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012