Modifications of the active sites distribution in the Ziegler‐Natta polymerization of propylene using Lewis acids

Heterogeneous Ziegler‐Natta precatalysts (with phthalate as internal donor) were modified by treatments with various Lewis acids (MCl_n with M = Ga, Sn, Si, and Sb and n = 3, 4, or 5) before their use in the polymerization of propylene. If performed on previously “detitanated” precatalysts, treatments with SnCl₄ and SiCl₄ lead to a slight activation but especially to an increase of the tacticity whereas GaCl₃ and SbCl₅ treatments deactivate the catalyst. The modification method applied to conventional unmodified precatalysts gave similar trends. A significant increase of tacticity (and/or of T_m) and a narrowing of the molecular weight distribution were observed in the case of SnCl₄ and SiCl₄ treatments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2631–2635, 2010