Enzyme-catalyzed polyester synthesis in organic medium: Ring-chain equilibrium

Enzyme-catalyzed synthesis of aliphatic, unsaturated and semi-aromatic polyesters from methyl diesters and diols was carried out in toluene at 60 degrees C in the presence of supported lipases. Whatever the monomer structure, rings were formed concurrently to linear chains excepted when dimethyl fumarate was used. The yield of rings depends on several parameters such as the monomer structure and the initial concentration of the reactive functions and strongly influences the average molar masses of the unfractionated samples. For aliphatic, unsaturated and semi-aromatic polyesters, the molar cyclization equilibrium constants (K) were determined and it would appear that the molar distribution of the ringed species obeys Jacobson-Stockmayer equation : LnK = LnB - 5/2 Lnn, where B and n represent a constant and the number of monomer units of each type in the ring, respectively.