Synthesis of aliphatic polyesters by controlled ring-opening polymerization of cyclic esters. Characterization, properties, transesterification reactions.

The polymerization of (D,L)-Lactide at room temperature in solution using Y (OCH(2)CH(2)OiPr)(3) and Ln(5)(mu-O)(OiPr)(13) with Ln = La, Sm, Y, Yb as i nitiators was studied. According to kinetic data, a controlled type polymer ization is observed for most of the systems. La mu-oxoisopropoxide is the m ast reactive initiator, but leads to a substantial broadening of molecular weight distribution at high conversions. The nature of transesterification reactions was studied by SEC, C-13 NMR and MALDI-TOF MS techniques. For Sm and Y-mu-oxo initiators only limited intermolecular ester exchange occurs, while with La mu-oxoinitiator and with Y(OCH(2)CH(2)OiPr)(3) initiator, but after a long time of the polymerization reaction, both inter and intramole cular transesterification occur with formation of cyclics.