Synthesis and degradability of a novel aliphatic polyester based on L-lactide and sorbitol .3.

Reaction of L-lactide (LLA) with sorbitol (SE) in the presence of stannous octoate (Sn oct), tetraphenyl tin (TPhT) and several other catalysts gave a series of novel polyesters. Several techniques such as nuclear magnetic resonance (n.m.r.) and Fourier transform infra-red (FTi.r.) spectroscopy, gel permeation chromatography (g.p.c.) and differential scanning calorimetry (d.s.c.) were used in order to characterize these polymers. The crystallinity of the polyesters was found to depend on the molar ratio of LLA to SB, i.e. when LLA/SB > 20/1 or > 40/1 (for Sn oct or TPhT, respectively) the polyesters are semicrystalline (from d.s.c. results) whereas at molar ratios of LLA to SE which are lower than those mentioned above the polymers become amorphous. High SE contents have an adverse effect on the thermal properties (i.e. lower T-g, T-m, and Delta H-m) and the molecular weight distribution (lower M(n) and M(w)) but they enhance their biodegradability. The latter was tested in terms of enzymatic and alkali hydrolysis. Both total organic carbon (TOC) and g.p.c. measurements confirmed the degradation of the polyesters at different hydrolysis modes.