Preparation and characterization of biodegradable poly(lactic acid)-block-poly(ε-caprolactone) multiblock copolymer

Biodegradable copolymers of poly(lactic acid)-block-poly(epsilon-caprolactone) (PLA-b-PCL) were successfully prepared by two steps. In the first step, lactic acid monomer is oligomerized to low molecular weight prepolymer and copolymerized with the (L-caprolactone) diol to prepolymer, and then the molecular weight is raised by joining prepolymer chains together using 1,6-hexamethylene diisocyanate (HDI) as the chain extender. The polymer was carefully characterized by using H-1-NMR analysis, gel permeation chromatography (GPC) thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). The results of H-1-NMR and TGA indicate PLA-b-PCL prepolymer with number average molecular weights (M-n) of 4000-6000 were obtained. When PCL-diols are 10 wt%, copolymer is better for chain extension reaction to obtain the polymer with high molecular weight. After chain extension, the weight average molecular weight can reach 250,000 g/mol, as determined by GPC, when the molar ratio of -NCO to -OH was 3:1. DSC curve showed that the degree of crystallization of PLA-PCL copolymer was low, even became amorphous after chain extended reaction. The product exhibits superior mechanical properties with elongation at break above 297% that is much higher than that of PLA chain extended products. Copyright (C) 2009 John Wiley & Sons, Ltd.