Enzymatic Hydrolysis of Poly(L-lactide-co-.EPSILON.-caprolactone)s.

Abstract

Biodegradability of poly (L-lactide-co-e-caprolactone) s was evaluated with both enzymatic and non-enzymatic hydrolysis. The hydrolysis was carried out in phosphate buffer (pH 7.0) at 37°C for 24h and the enzymes used were lipases from Rhizopus arrhizus, Rhizopus delemar, and Candida cvlindracea. The hydrolyzability of these polymers was evaluated with measurement of TOC values (total organic carbon concentration) which show the amount of the hydrolyzed water-soluble products. The copolymers were synthesized by ring-opening polymerization using tin (II) octanoate as initiator. Although poly (L-lactide), poly (e-caprolactone) and their random copolymers were hydrolyzed with all three above mentioned lipases, Rhizopus arrhizus and Rhizopus delemar lipases proved to be the most effective. The extent of enzymatic hydrolysis was considerably affected by copolymer composition. The copolymer, which showed the highest susceptibility to hydrolysis, was the one containing 82 mol% e-caprolactone unit. The polymers were also non-enzymatically hydrolysed (70°C, 1 week) and the results were similar to those of enzymatic hydrolysis showing clearly the influence of copolymer composition on the TOC results. However, TOC measurements showed that the L-lactide rich copolymers, and in particular the one with 80 mol% lactide content, were more susceptible to hydrolysis. These results suggest that poly (e-caprolactone) can be easily degraded with lipase, whereas poly (L-lactide) can be also degraded with simple hydrolysis. e-Caprolactone rich oligomers, 6-hydroxycaproic acid, and lactic acid were identified with NMR as the main products of hydrolysis.