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 stan nous octoate (Sn oct), tetraphenyl tin (TPhT) and several other cataly sts gave a series of novel polyesters. Several techniques such as nucl ear magnetic resonance (n.m.r.) and Fourier transform infra-red (FTi.r .) spectroscopy, gel permeation chromatography (g.p.c.) and differenti al scanning calorimetry (d.s.c.) were used in order to characterize th ese 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 (fo r Sn oct or TPhT, respectively) the polyesters are semicrystalline (fr om d.s.c. results) whereas at molar ratios of LLA to SE which are lowe r than those mentioned above the polymers become amorphous. High SE co ntents 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 t ested 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.