Catalysis
Mikhail A. Matsko; Vladimir A. Zakharov; Marina I. Nikolaeva; Tatiana B. Mikenas
Abstract
The data on the effect of ethylene concentration on polymerization rate for several modifications of modern highly active titanium–magnesium catalysts TiCl4/MgCl2 are presented. These catalysts differ in titanium content and conditions of support preparation, activities, and the shape of kinetic ...
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The data on the effect of ethylene concentration on polymerization rate for several modifications of modern highly active titanium–magnesium catalysts TiCl4/MgCl2 are presented. These catalysts differ in titanium content and conditions of support preparation, activities, and the shape of kinetic curves. It is found that the observed order of polymerization rate with respect to ethylene in the range of ethylene pressures of 0.5–6 bar is 1.8-2.1 for all catalysts used (polymerization at 80°C, AlEt3 used as a cocatalyst). When AlEt3 was replaced with Al(i-Bu)3, the reaction order decreased to 1.3-1.4. In order to elucidate the possible reasons for the observed high order with respect to ethylene, we analyzed the data on the effect of monomer concentration on the molecular weight of polyethylene. The results gave grounds for suggesting that the observed order with respect to monomer is attributable to the effect of ethylene concentration on the number of active sites. The possible reaction scheme explaining the nonlinear dependence of the polymerization rate on monomer concentration was proposed based on these data.
Catalysis
Toshiaki Taniike; Keisuke Goto; Minoru Terano
Abstract
Heterogeneous Ziegler-Natta and homogeneous metallocene catalysts exhibit greatly different active sitenature in olefin polymerization. In our previous study, it was reported that MgCl2-supported titanocenecatalysts can generate both Ziegler-Natta-type and metallocene-type active sites according to the ...
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Heterogeneous Ziegler-Natta and homogeneous metallocene catalysts exhibit greatly different active sitenature in olefin polymerization. In our previous study, it was reported that MgCl2-supported titanocenecatalysts can generate both Ziegler-Natta-type and metallocene-type active sites according to the type of activators.The dual active site nature of the supported titanocene catalysts was further explored in the present study: The influence of the ligand structure of titanocene precursors was studied on the nature of active sites when supported on MgCl2 in ethylene and propylene homopolymerization, and ethylene/1-hexene copolymerization. It was found that the reducibility of titanocene precursors by alkylaluminum is closely related to the appearance of the dual active site nature, while the kind of olefin did not affect the type of active sites formed during polymerization. The Ziegler-Natta-type active sites produced poorly isotactic polypropylene and less branched polyethylene, while the metallocene-type active sites produced atactic polypropylene and exhibited much higher incorporation efficiency for 1-hexene.
