Polymerization of lactides and lactones. II. Ring-opening polymerization of epsilon-caprolactone and DL-lactide by organoacid rare earth compounds

Ring-opening polymerization of lactone and lactide have been initiated with rare earth organoacid compounds, such as lanthanum acetate in bulk. The po lymerization mechanism is in agreement with the "nonionic-coordination-inse rtion" mechanism, which involves the selective cleavage of the acyl-oxygen bond of the monomer. These organoacid rare earth initiators can give high y ield of medium to high molecular weight products. An interesting aspect of this investigation is the good agreement between the performance of the ini tiator and the solubility of the initiator in the monomer. However, the rel atively slow initiation step makes it difficult to control the molecular we ight and results in a broad molecular weight distributions. (C) 1999 John W iley & Sons, Inc.