Novel monotitanocene and methylaluminoxane catalyst for syndiospecific polymerization of styrene

Abstract

Syndiotactic polystyrene (sPS) was synthesized with a novel monotitanocene complex of η 5 -pentamethylcyclopentadienyltri-4-methoxyphenoxy titanium [Cp * Ti(OC 6 H 4 OCH 3 ) 3 ] activated by methylaluminoxane (MAO) in different polymerization media, including heptane, toluene, chlorobenzene, and neat styrene. In all cases bulk polymerization produced sPS with the highest activity and molecular weight. Solution polymerization produced much better activity in heptane than in the other solvents. Using a solvent with a higher dipole moment, such as chlorobenzene resulted in lower activity and syndiotacticity because of the stronger coordination of solvent with the Ti(III) active species, which controlled syndiospecific polymerization of styrene. With bulk polymerization at a higher polymerization temperature the Cp*Ti(OC 6 H 4 OCH 3 ) 3 -MAO catalyst produced sPS with high catalytic activity and molecular weight. The external addition of triisobutylaluminum (TIBA) to the Cp * Ti(OC 6 H 4 OCH 3 ) 3 -MAO system catalyzing styrene polymerization led to significant improvement of activity at a lower Al:Ti molar ratio, while the syndiotacticity and molecular weight of the yields were little affected.