Abstract
Titanium complexes (1–3) of unsymmetric N2O2 ligands (H2L) were prepared. The reaction of H2L with NaH and then with TiCl4 in THF gave a mononuclear complex LTiCl2 (1). In the presence of 0.5 equiv of water in THF, the hydrolysis of complex 1 produced an oxo-bridged dinuclear complex (μ-O)[LTiCl]2 (2). The mononuclear Ti complex LTi(OiPr)2 (3) was prepared by combining H2L with Ti(OiPr)4 in dry toluene. Complexes 1–3 are able to catalyze the living control ring-opening polymerization (ROP) of lactide to afford polylactide (PLA) with a narrow molecular weight distribution (Mw/Mn = 1.03–1.19). The kinetic studies show a first-order dependency in monomer. The microstructure analysis of the resultant polymer implies that the complexes possess isotactic selectivity and the isotactic-riched polylactide (Pm = 0.68–0.73) can be produced. The polymerization of l-lactide proceeds at a faster rate than the polymerization of rac-lactide, which is consistent with the isoselectivity in the polymerization.
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