Active center determinations on MgCl2-supported fourth- and fifth-generation Ziegler-Natta catalysts for propylene polymerization

Active center determinations on different Ziegler-Natta polypropylene catalysts, comprising MgCl2, TiCl4, and either a diether or a phthalate ester as internal donor, have been carried out by quenching propylene polymerization with tritiated ethanol, followed by radiochemical analysis of the resulting polymers. The purpose of this study was to determine the factors contributing to the high activities of the catalyst system MgCl2/TiCl4/diether-AlEt3. Active center contents (C*) in the range 2-8% (of total Ti present) were measured and a strong correlation between catalyst activity and active center content was found, indicating that the high activity of the diether-containing catalysts is due to an increased proportion of active centers rather than to a difference in propagation rate coefficients. (c) 2006 Wiley Periodicals, Inc.