Ring opening polymerization of lactide promoted by alcoholyzed heteroscorpionate aluminum complexes

Abstract

Abstract The alcoholysis of the heteroscorpionate methyl aluminum complex (bpzmp)AlMe 2 ( 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 κ 2 ‐N,O − coordinated bpzmp ligand and one η 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. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3632–3639, 2010