Salen Complexes of Zirconium and Hafnium: Synthesis, Structural Characterization, Controlled Hydrolysis, and Solvent-Free Ring-Opening Polymerization of Cyclic Esters and Lactides

Dinuclear salen compounds of zirconium and hafnium are efficient initiators for the solvent-free ring-opening polymerization of cyclic ester monomers and lactides. There is a correlation between the theoretical and experimental number-average molecular weights (Mn's) in these polymerizations. Polymerization of β-butyrolactone gives poly(3-hydroxybutyrate) with a good Mn and molecular weight distribution.