Syndiotactic polymerization of styrene catalyzed by dinuclear half-titanocenes with bridging hexamethyltrisiloxanediylbis(cyclopentadienyl) and pentamethylenediylbis(cyclopentadienyl) ligands

The styrene polymerizations were carried out with the new dinuclear half-titanocenes, hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride) (1) and pentamethylenediylbis (cyclopentadienyltitanium trichloride) (2) in the presence of a modified methylaluminoxane cocatalyst. The styrene polymerization behavior of the above dinuclear titanocene catalysts and the property of the obtained polystyrene (PS) were examined and compared with those of PS obtained by mononuclear CpTiCl₃. For a given polymerization condition, the catalyst activity was in the following order; CpTiCl₃>2>1. The syndiotactic index (SI) of PS was dependent on the catalyst structure and decreased in the order of 1>CpTiCl₃>2. The weight-average molecular weight (M_ω) of PS produced with dinuclear 1 and 2 was much higher than that of PS generated from mononuclear CpTiCl₃, and the polydispersity index (M_ω/M_ν) of the polymer by 1 and especially by 2 was larger than that of the polymer by CpTiCl₃. Although the pentamethylene-bridged titanocene 2 exhibited higher activity and lower SI of PS than the hexamethytrisiloxane-bridged complex 1, the M_ω and M_ω/M_ν of PS prepared with the dinuclear half-titanocene 2 were almost identical to those of PS with complex 1.