Hartree-Fock and density functional theory analysis of propylene insertionin Al(CH3)(3)/TiCl3/TiO2 (red.) in the presence of a Lewis base

Titanium tetrachloride heterogenized on reduced TiO2 was recently described as an active catalyst for ethylene polymerization. This catalytic system a lso permits propylene polymerization with lower activity, however, with low polydispersity, high molecular weight and with the good isotacticity of 78 %. The isotacticity of this polymer can be increased by addition of a Lewis base. The behavior of the active site, in the presence of a Lewis base, wa s studied by ab initio Hartree-Fock and density functional theory. The atom ic charge values obtained suggest that methyl benzoate used as a Lewis base makes the active site more susceptible to coordination with propylene. (C) 1999 Elsevier Science B.V. All rights reserved.