Controlled Polymerization of dl-Lactide and ε-Caprolactone by Structurally Well-Defined Alkoxo-Bridged Di- and Triyttrium(III) Complexes

Abstract

We have prepared the yttrium(III) alkoxides [(LMe2)(HLMe2)Y3(OCH2C6H5)4] (3) and [(S-LMe)Y]2·2(HOCH2C6H5) (1·2BnOH) through treatment of two previously developed complexes with benzyl alcohol. Complex 3 possesses a novel cluster structure that appears to be retained in solution and is capable of polymerizing both dl-lactide (LA) and e-caprolactone (CL). The polymerizations are controlled as evidenced by the linear nature of molecular weight versus conversion plots and [M]/[3] ratios. The kinetics of LA polymerization using 3 are first-order with respect to the monomer at low [LA]/[Y] ratios. The polymerization of CL is zero-order in monomer. Complex 1·2BnOH possesses a dimeric structure previously seen in both the solid and solution state. However, the added presence of benzyl alcohol moieties in 1·2BnOH increases the rate of LA polymerization and allows for control over the molecular weights of isolated polylactide, a feature unseen in earlier reported dimers. The complex 1·2BnOH is not active for the po...