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 (μ‐O)(OiPr) 13 with Ln = La, Sm, Y, Yb as initiators was studied. According to kinetic data, a controlled type polymerization is observed for most of the systems. La μ‐oxoisopropoxide is the most reactive initiator, but leads to a substantial broadening of molecular weight distribution at high conversions. The nature of transesterification reactions was studied by SEC, 13 C NMR and MALDI‐TOF MS techniques. For Sm and Y‐μ‐oxo initiators only limited intermolecular ester exchange occurs, while with La μ‐oxoinitiator and with Y(OCH 2 CH 2 OiPr) 3 initiator, but after a long time of the polymerization reaction, both inter and intramolecular transesterification occur with formation of cyclics.