Styrene polymerizations with a series of nonbridged half-titanocenes of the type Cp′TiCl 2(L) [L ) O-2,6-i Pr2C6H3, Cp′ ) , C5Me5 (Cp*, 4′)] have been explored in the presence of MAO cocatalyst under various conditions. The catalytic activities for syndiospecific styrene polymerization with a series of half-titanocenes containing an aryloxo ligand, Cp′TiCl 2(O-2,6-i Pr2C6H3), were higher than those with the trichloro analogues, Cp′TiCl3, and the activity with a series of Cp* analogues (4, 4′, 5-8) and 1,3-Me2C5H3 analogues (2, 2′, 9, 10) were highly dependent upon the anionic donor ligand used. ( t BuC5H4)TiCl2(O-2,6-i Pr2C6H3) (11) exhibited a relatively high catalytic activity for syndiospecific styrene polymerization at 25°C when both [PhMe 2NH]B(C6F5)4 and a mixture of Al i Bu3/Al(n-C8H17)3 were used as the cocatalyst, and the activity with a series of (1,3-Me2C5H3)TiCl2(OAr) depended on the aryloxide ligand used. The role of the anionic donor ligand, like the aryloxide ligand, toward both the catalytic activity and the Mw values of polystyrene has thus been observed irrespective of the kind of cocatalyst employed.

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