Propylene polymerization over MgCl2-supported TiCl4 catalysts bearing different amounts of a diether internal electron donor: Extrapolation to the role of internal electron donor on active site

Abstract

In this work, the composition of MgCl2-supported Ziegler-Natta (ZN) catalysts bearing different amounts of 9,9-bis(methoxymethyl)fluorine (BMMF) and the propylene polymerization over these catalysts are investigated. Based on the experimental results, the models of active sites suitable for ZN catalysts with/without internal donor BMMF are established, and they can be described as follows: atactic site (I)—isolated TiCl4 monomeric species on the (110) lateral cut (around which there is no complexes), weakly isospecific site (II)—semi-isolated and surrounded TiCl4 monomeric species on the (110) lateral cut (in the vicinity of which BMMF or other TiCl4 is adsorbed), and highly isospecific site (III)—dimeric TiCl4 species (Ti2Cl8) on the (104) lateral cut. Meanwhile, the mechanism underlying the role of BMMF on active sites is revealed (i) convert atactic sites (I) to weakly isospecific site (II) by occupying either or both of L1 or/and L2 vacancies around site; (ii) improve the isotacticity of weakly isospecific site (II) in donor-free ZN catalyst by adsorbing at L2 vacancy or/and replacing the Cl for TiCl4 at L1; and (iii) replace highly isospecific site (III). In addition, these roles of BMMF are successively achieved according to the amount of BMMF added. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012