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 (lipozyme(R) and novozyme(R)). 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 degrees C works best when novozyme(R) 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. (C) 1995 John Wiley & Sons, Inc.