Abstract
Zirconium and titanium complexes containing hydrotris(pyrazolyl)borate (Tp) or hydrotris(3,5-dimethylpyrazolyl)borate (Tp *) as a ligand have been examined as polymerization precatalysts for ethylene, propylene and styrene. Activation of the group 4 transition-metal complexes by methylaluminoxane exhibits a greater catalytic activity in ethylene polymerization for TpMCl 3 (M=Zr, Ti) than for the corresponding mono-cyclopentadienyl analogue, CpMCl 3. Dimethyl substitution on the pyrazolyl groups enhances the activity for the Zr complex (Tp *ZrCl 3), but not for the Ti complex (Tp *TiCl 3). Complete substitution of O tBu or OPh groups for Cl ligands in Tp *ZrCl 3 greatly decreases the activity. Mono substitution of an OPh group for one Cl ligand in Tp *TiCl 3 does not affect the activity. The addition of propylene comonomer reduces the catalytic activity of Zr complexes containing Tp or Tp * to a considerable degree. The Tp and Tp * complexes of Zr and Ti produce atactic polymers from styrene.
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