Controlled ring-opening polymerization of ε-caprolactone promoted by in situ formed yttrium alkoxides

The ring-opening polymerization of epsilon-caprolactone has been initiated by [tris(hexamethyl-disilyl)amide]yttrium in the presence of an excess of 2-propanol. This initiating system is very active even at high alcohol-to-Ti molar ratio. Polymers with controlled molecular parameters (M-n, end groups) and low dispersity are formed as result of fast alkoxide/alcohol exchange. At molar excess of 2-propanol higher than 100, this exchange is no longer quantitative. The in situ formed active species involved in this new initiating system are different from those ones present in the commercial yttrium oxo-isopropoxide Y-5(mu-O)((OPT)-P-i)(13) cluster. Evidence is provided by H-1 NMR spectroscopy.