Recent development of catalysts for syndiospecific polymerization of styrene

Catalysts for syndiospecific polymerization of styrene are examined. Among the transition metal complexes, complexes with titanium and one cyclopentadienyl(Cp) ligand show high catalyst activity. Titanium complexes with different substituent groups on Cp ligand were examined and a good relationship between electron density of titanium and the space for styrene coordination was found. The bulky substituent groups reduce the catalyst activity and electron donative substitution groups increase the catalyst activity. Small amount of hydrogen increases the catalyst activity. However, excess amount of hydrogen makes molecular weight distribution broaden. There seems to be two kinds of active site for the styrene polymerization under the conditions. Titanium complexes with various types of tetraphenylborates were examined. The number of fluorine on the phenyl group of berate improves the catalyst activity and by-products from the reaction of triisobutylaluminum, berate and titanium complex may coordinate the active site and decrease the catalyst activity.