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Group 4 Salalen Complexes and Their Application for the Ring-Opening Polymerization of rac-Lactide

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journal contribution
posted on 02.08.2010, 00:00 by Emma L. Whitelaw, Matthew D. Jones, Mary F. Mahon
In this paper, we report the preparation and characterization of a series of unsymmetrical group 4 metal complexes based on ONNO salalen-type ligands. In these examples, the ligand is unsymmetrical with an amine and an imine nitrogen center. All complexes {except Hf(3)(OiPr)2} adopt a β-cis configuration in the solid state, which is also in agreement with solution-state NMR spectroscopic measurements. The complexes have been tested for the ROP of rac-lactide (both in solution and under melt conditions). Narrow polydispersities have been seen (1.07−1.82). The Ti(IV) complexes produce atactic PLA, whereas the Zr(IV) complexes form PLA with a heterotactic bias. Hf(IV) complexes have been shown to produce isotactic PLA with a Pm of 0.75. The kinetics for all initiators have been investigated and are discussed.