Controlled polymerization of DL-lactide and ε-caprolactone by structurally well-defined alkoxo-bridged di- and triyttrium(III) complexes

We have prepared the yttrium(III) alkoxides [(L-Me2)(HLMe2)Y-3(OCH2C6H5)(4)] (3) and [(S-L-Me)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 epsilon-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]I[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 polymerization of CL.