Catalysis
Zenghui Zhao; Tatiana Mikenas; Vladimir Aleksandrovich Zakharov; Marina Nikolaeva; Mikhail Matsko; Elena Bessudnova; Wei Wu
Abstract
The new highly active supported vanadium-magnesium catalyst (VMC) has been studied in α-olefin (1-butene, 1-hexene)/ ethylene copolymerization in the presence of hydrogen. Data on the effect of α-olefin/ethylene ratio in copolymerization on the content of branchings in copolymers, kinetic ...
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The new highly active supported vanadium-magnesium catalyst (VMC) has been studied in α-olefin (1-butene, 1-hexene)/ ethylene copolymerization in the presence of hydrogen. Data on the effect of α-olefin/ethylene ratio in copolymerization on the content of branchings in copolymers, kinetic profile, copolymer yield, molecular weight and molecular weight distribution of copolymers have been obtained. It was found that both α-olefins are effective chain transfer agents in the ethylene-α-olefins copolymerization. The copolymerization ability of VMC is much higher than that of the well known titanium-magnesium catalysts. It was found that the use of optimal conditions of ethylene/α-olefin polymerization on the VMC catalyst makes it possible to obtain copolymers with a high yield (10-16 kg gcat-1 cat for 2 h) the copolymers having broad and bimodal MWD. Data on the branchings distribution in copolymers prepared with VMC catalyst have been obtained via fractionation of copolymers on the fractions with narrow polydispersity (Mw/Mn ≈ 2). Quite a uniform distribution of branchings over fractions with different molecular weight was found in distinction to inhomogeneous distribution of branchings in copolymers produced over the well known supported titaniu-magnesium catalyst.
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.
