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(R)). 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 (BSH) and terephthalate (BTH). The trimeric fragments tetramethyl disuccinate (SBSH) and succinate terephthalate (SBTH), 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.