Bis(phenyl-β-diketonato)titanium(IV) ethoxide complexes: Ring-opening polymerization of L-lactide by solvent-free microwave irradiation

A range of functionalized bis(phenyl-β-diketonato)titanium(IV) ethoxide complexes of the type [Ti(L)2(OEt)2], containing two asymmetric or symmetric phenyl-β-diketonate ligands (L), have been synthesized and fully characterized. Single crystal X-ray diffraction has been used to confirm that all structures crystallize with the ethoxide ancillary ligands in a cis arrangement and NMR spectra show characteristic ligand rearrangement in solution. The complexes have been screened as catalysts in the ring-opening polymerization (ROP) of l-lactide (L-LA) to yield polylactide (PLA), by using microwave (MW) and conventional heating. The resulting polymers have high molecular weights but high polydispersity index (PDI) which are suggestive of transesterification. However, unlike conventional heating methods, the polymerization by MW reaction leads to a retention in stereochemistry of the resulting polymer in significantly shorter time periods.