Synthesis and characterization of poly(L-lactic acid)-poly(ε-caprolactone) multiblock copolymers by melt polycondensation

Abstract

New multiblock copolymers derived from poly(L-lactic acid) (PLLA) and poly(ε-caprolactone) (PCL) were prepared with the coupling reaction between PLLA and PCL oligomers with - NCO terminals. Fourier transform infrared (FTIR), 13C NMR, and differential scanning calorimetry (DSC) were used to characterize the copolymers and the results showed that PLLA and PCL were coupled by the reaction between - NCO groups at the end of the PCL and - OH (or - COOH) groups at the end of the PLLA. DSC data indicated that the different compositions of PLLA and PCL had an influence on the thermal and crystallization properties including the glass-transition temperature (T g), melting temperature (TM), crystallizing temperature (Tc), melting enthalpy (ΔHm), crystallizing enthalpy (ΔHc), and crystallinity. Gel permeation chromatography (GPC) was employed to study the effect of the composition of PLLA and PCL and reaction time on the molecular weight and the molecular weight distribution of the copolymers. The weight-average molecular weight of PLLA -PCL multiblock copolymers was up to 180,000 at a composition of 60% PLLA and 40% PCL, whereas that of the homopolymer of PLLA was only 14,000. A polarized optical microscope was used to observe the crystalline morphology of copolymers; the results showed that all polymers exhibited a spherulitic morphology. © 2004 Wiley Periodicals, Inc.