Evidence for Selective Hydrolysis of Aliphatic Copolyesters Induced by Lipase Catalysis

High molar mass random poly(butylene succinate-co-butylene sebacate), P(BS-co-BSe), and poly(butylene succinate-co-butylene adipate), P(BS-co-BA), with different compn., were synthesized and subjected to enzymic hydrolysis by Lipase from Mucor miehei or from Rhizopus arrhizus. The enzymic hydrolysis of P(BS-co-BSe)s and P(BS-co-BA)s films produced a mixt. of water-sol. monomers and co-oligomers that were sepd. and identified by online high performance liq. chromatog./electrospray ionization mass spectrometry (HPLC/ESI-MS). Optimization of the HPLC anal. allowed the sepn. of isobar co-oligomers, differing only for the co-monomers sequence. Oligomers with the same monomer compn. and molar mass but different sequence were identified by HPLC/ESI-MS-MS online anal. The results obtained show a preferential hydrolytic cleavage induced by the lipases used. In particular, these enzymes prefer cleaving sebacic ester bonds in P(BS-co-BSe) copolymers, whereas succinic ester bonds appear to be hydrolyzed faster than adipic ester bonds in P(BS-co-BA) copolyesters. 1H NMR anal. further substantiates these findings. The primary products generated by lipase hydrolysis of polyester films underwent further degrdn. at longer reaction times. The HPLC/ESI-MS anal. of these mixts. at various times provided the first evidence that lipase catalysis is active also in water soln., a hydrophobic effect induced by the aliph. units of these polyesters.