Syndiospecific Polymerization of Styrene with Half-Sandwich Titanocene Catalysts. Influence of Ligand Pattern on Polymerization Behavior

As modifications of the effective catalyst precursor for syndiospecific styrene polymerization, namely [2-Me-thBenz[ e ]Ind]TiCl 3 ( Ic ), [2,3-Me 2 -thBenz[ e ]Ind]TiCl 3 ( IIc ), [1,2,3-Me 3 -thBenz[ e ]Ind]TiCl 3 ( IIIc ), and [2-Me-3-Ph-thBenz[ e ]Ind]TiCl 3 ( IVc ) have been synthesized to examine the influence of ligand pattern on the catalyst activity and polymer properties. These complexes, activated by methylaluminoxane (MAO), showed high activities compared with previously employed titanocene catalysts. Of all titanocenes examined, [2-Me-3-Ph-thBenz[ e ]Ind]TiCl 3 ( IVc )/MAO showed the highest activity and stability at an even fairly low Al/Ti ratio of 1000, revealed the excellent control over the stereoregular insertion of monomer, and exhibited a significant increase of the ratio of the propagation rates to chain transfer termination as evidenced by the kinetic results, thus producing polymers with the highest syndiotacticity and molecular weight. The kinetic investigations, combined with the EPR spectrum and polymerization experiments, showed that the higher activity of tetrahydrobenz[ e ]indenyl-based systems is due to a great number of active species.