Enzyme-catalyzed synthesis of aliphatic polyesters in organic media: Study of transesterification equilibrium shift and characterization of cyclic compounds

Enzyme-catalyzed synthesis of aliphatic polyesters in organic media from methyl diesters and diols was carried out at stoechiometric ratio in the presence of supported lipases (li-pozyme^® and novozyme^®). Two systems were studied to shift the thermodynamic equilibrium which limits the conversion. In the first one, the solution flows through a molecular sieve in which methanol is adsorbed. In the second one, methanol is eliminated by nitrogen bubbling. The system with nitrogen bubbling in hydrophobic solvents at 60°C works best when novozyme^® is used as catalyst. Despite a high fractional conversion (p> 0.99), the number-average molar mass is not very high (M?;_n = 3050 eq. PS). In relation to the nature of monomers, cycles with DP = 2–20 were characterized by chromatographic analyses and mass spectrometry. Their formation explains why high polycondensates cannot be obtained. © 1995 John Wiley & Sons, Inc.