(A) study on the homogeneous and supported metallocene catalysts for olefin polymerization

Abstract

Olefin polymerization was performed to study the methodologies involved in the preparation of supported metallocene catalyst systems and the nature of the corresponding active sites involved in olefin polymerization. The influence of modification and heterogenization of homogeneous metallocenes on catalytic performances and on the final polymer properties was also examined. The new homogeneous polymerization catalysts, $Cp^*M(TEA)$ (M = Ti, Zr, and Hf, TEA = triethoxyamine), were used for ethylene homopolymerization and ethylene/1-hexene copolymerization to correlate catalytic behaviors of these catalyst with the polymer properties such as molecular weight and melting temperature. The catalytic activities in ethylene polymerization increased with mole ratio of Al/metal and decreased in the order of $Cp^*Ti(TEA) ＞ Cp^*Zr(TEA)$ ≫ Cp^*Hf(TEA)$. However, molecular weight (Mv) and melting temperature (Tm) of polyethylene obtained over $Cp^*Zr(TEA)/MAO$ catalyst were much larger and higher than those over Zr or Hf catalysts. Active species of each catalyst was different due to different electronic and steric effects of the ligands on active metal center. Copolymerization with $Cp^*Ti(TEA)$ catalyst resulted in a good incorporation of 1-hexene into the polyethylene main chain but did not with two other catalysts. The content of 1-hexene comonomer in the polymer main chain increased with the $C_6/C_2$ mole ratio in the feed. The role of ancillary TEA ligands in $Cp^*Ti(TEA)/MAO$ was found very different from that of ancillary Cl ligand in $Cp^*TiCl_3$. The chlorine ligand was detached from the central Ti atom which was activated to $Ti^{3+}$, while the TEA ligand remained attached to the metal atom during the activation by MAO. Styrene homopolymerization and styrene-ethylene copolymerization were carried out using various titanium-based organometallic catalysts with methylaluminoxane as a cocatalyst. Activities in styrene homopolymerization, which were quite high ...