SYNTHESIS AND BIODEGRADABILITY OF NOVEL COPOLYESTERS CONTAINING GAMMA-BUTYROLACTONE UNITS

Copolymers were synthesized by ring-opening polymerization of gamma-bu tyrolactone (BL) with cyclicesters. Comonomers used were L-lactide (LL A), glycolide (GL), beta-propiolactone (PL), delta-valerolactone (VL) and epsilon-caprolactone (CL). Tetraphenyl tin was used as an initiato r. The copolymerization was carried out in bulk at 140 degrees C for 4 days and the polymers were characterized by H-1 n.m.r., C-13 n.m.r., g.p.c. and d.s.c. The BL contents of the copolymers varied in the rang e 0 and 26 mol%. The number average molecular weights were from 1.3 x 10(3) to 1.5 x 10(5). When a small amount of the BL unit was introduce d into the polymer chain, increased flexibility and excellent biodegra dability were imparted to the polymer. However, excess of BL resulted in low molecular weight polymers with substantially low yields. D.s.c. measurements showed that the copolymers had one single endothermic pe ak at lower temperatures than those of the T(m)s of each homopolymer. The BL rich copolymers were shown to be amorphous. The statistical nat ure of the synthesized copolymers was confirmed with n.m.r. analysis. The copolyesters were hydrolyzed in distilled water at 70 degrees C an d their hydrolyzability was found to be affected by the chemical struc ture and polymer composition. The hydrolyzability of glycolide or lact ide copolymers was high in comparison with other copolyesters. The BL- rich copolyesters were easily hydrolyzed. The copolymers were also hyd rolyzed with lipases from Rhizopus arrhizus, R. delemar and Candida cy lindracea in phosphate buffer solution (pH 7.0) at 37 degrees C. Copol ymers without substituents, such as the poly(BL-co-epsilon-caprolacton e)s, were easily enzymatically hydrolyzed. It is noteworthy that the n on-enzymatic hydrolysis was not affected by the presence of substituen ts. (C) 1997 Elsevier Science Ltd. All rights reserved.