Ring Opening Polymerization of Lactide Promoted by Alcoholyzed Heteroscorpionate Aluminum Complexes

The alcoholysis of the heteroscorpionate methyl aluminum complex (bpzmp)AlMe2 (1) (bpzmp = 2,4-di-tert-butyl-6-(bis-(3,5-dimethylpyrazol-1-yl)methyl)phenoxo), promoted both by phenol and isopropanol, has been investigated. The reaction of 1 with phenol afforded the dimeric mono(phenoxo) derivative 2, whereas the alcoholysis of 1 with the less acidic isopropanol involved the coordinated heteroscorpionate ligand and led to the tetrahedral complex 3 in which the aluminum atom is surrounded by one kappa(2)-N,O- coordinated bpzmp ligand and one eta(1)-O- coordinated ppzmp ligand (ppzmp = 2,4-di-tert-butyl-6-(i-propoxy-(3,5-dimethylpyrazol-1-yl)methyl)phenoxo). Complexes 1-3 have been tested in the ring opening polymerization (ROP) of L-lactide. The dimeric mono(phenoxo) derivative 2 was inactive in the ROP of L-lactide. Quite surprisingly, complex 3 was found to be active in ROP of L- and rac-lactide, showing a good molar-mass control. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3632-3639, 2010