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. © 2011 American Chemical Society.