A few considerations on some catalysts for olefin polymerization

Among many precursors and catalysts for alpha-olefins polymerization, one seems to be particularly interesting, because it has not been completely clarified yet. We refer especially to precursors obtained via reaction between Mg-alkyls and SiCl4. The products of this reaction are not well known; in fact, under some operating conditions, a special form of MgCl2 is obtained, showing x-ray diffraction peaks in the angular region lower than 15° (2 theta), which corresponds to the 5.9 A interplanar spacing, characteristic of alpha-MgCl2. Under other conditions, MgCl2 is obtained in the well known and strongly disordered delta structure. By employing these precursors, some catalytic systems for alpha-olefins polymerization have been prepared. In this paper, the peculiar aspects of these precursors and catalysts are described, particularly focusing on the correlation between structure and performances in ethylene and propylene polymerization.