Mechanism of enzymatic hydrolysis of poly(butylene succinate) and poly(butylene succinate-co-L-lactate) with a lipase from Pseudomonas cepacia

Enzymatic hydrolysis of poly(butylene succinate) (PBS) and poly(butylene succinate-co-L-lactate) (PBSL) has been studied by using a lipase originated from Pseudomonas cepacia. It has been found that the drawn fibers of PBSL are readily hydrolyzed by the action of the lipase, while those of PBS undergo little enzymatic hydrolysis. Since the polymer films of PBS and PBSL are readily hydrolyzed under the same conditions, the enzymatic hydrolysis should depend not only on the crystallinity but also on the molecular orientation. The molecular weight of the samples gradually decreases with incubation time, because nonspecific hydrolysis occurs on the main chains of both PBS and PBSL even in the absence of lipase. The enzymatic hydrolysis of PBS and PBSL gives 4-hydroxybutyl succinate (HBS) as the main product with traces of succinic acid and butane-1,4-diol together with L-lactic acid in the case of PBSL. In addition, the hydrolysis rate of the carboxyl end-capped PBS is much slower than that of the original or hydroxyl end-capped PBS. These results imply a hydrolysis mechanism involving the preferential exo-type chain scission from the carboxyl terminals.