Studies on the enzymatic hydrolysis of polyesters. II. Aliphatic–aromatic copolyesters

Abstract

The dependence of the enzymatic degradation of aliphatic–aromatic copolyesters on the polymer structure has been investigated. A number of defined model copolyesters containing terephthalate units as aromatic component were synthesized. The model polymers included random copolyesters, block copolyesters and also strictly alternating copolyesters, which were made from especially synthesized and purified pre-building blocks. The biodegradability was evaluated applying a laboratory degradation test under well-defined conditions with a lipase from Pseudomonas sp. It could clearly be proven that the selectivity of the lipase concerning the aliphatic or aromatic environment near the ester bonds is not the predominant factor controlling the biodegradability of the copolyesters. As already described for aliphatic homo polyesters the biodegradation rate of the copolyesters is mainly controlled by the chain mobility of the polymers, being correlated with the difference between the melting point of the polyester and the degradation temperature. The presence of longer aliphatic domains, e.g., in block copolyesters does not facilitate the hydrolytic attack by the lipase, but longer aromatic sequences, which control the melting point of the crystalline regions, reduce the biodegradation rate. The concept of chain mobility seems to be a quite universal way to describe and predict the biodegradation rate of synthetic polyesters, independent on their composition or micro-structure.