Reaction mechanism of enzymatic degradation of poly(butylene succinate-co-terephthalate) (PBST) with a Lipase originated from Pseudomonas cepacia

An aliphatic/aromatic copolyester, poly(butylene succinate-co-terephthalate) (PBST), was prepared to investigate the effect of the aromatic units on the enzymatic degradation of the poly(butylene succinate) (PBS) derivatives in the presence of a lipase originated from Pseudomonas cepacia (Lipase PS®). The degradability of PBST was found to increase with increasing BS content. The degradation products were analyzed in detail by liquid chromatograph mass spectrometry (LC-MS). A hexamer containing one terephthalate unit was the largest fragment among the diverse fragments detected, while a pentamer was the largest one consisting only of succinate units. The oligomeric fragments cut out from the polymer chain were involved in the secondary hydrolysis into 4-hydroxybutyl succinate (BS_H) and terephthalate (BT_H). The trimeric fragments tetramethyl disuccinate (SBS_H) and succinate terephthalate (SBT_H), having both carboxyl end groups, were slowly hydrolyzed by a nonspecific mechanism. Based on these data, the overall mechanism of the enzymatic hydrolysis of this aliphatic/ aromatic copolyester is proposed, in which PBST undergoes endo hydrolysis.