The influence of magnesium dichloride as support on molecular weights of the polyethylenes produced by Ziegler-Natta catalyst

Document Type : Original research

Authors

Boreskov Institute of Catalysis SB RAS, pr. Akademika Lavrentieva, 5, 630090 Novosibirsk, Russia

Abstract

The paper presents data on the effect exerted by magnesium dichloride in Ziegler-Natta catalysts on the activity and molecular weight of polyethylene (PE) produced by ethylene polymerization in the absence or presence of hydrogen. It was found that ethylene polymerization in the absence of hydrogen over titanium-magnesium catalysts (TMCs) with different ratio of titanium chloride and magnesium dichloride (Ti/Mg = 0.5 and 0.07), oxidation state of titanium (TiCl3 or TiCl4) and structural characteristics of the catalysts leads to the formation of PE with a close molecular weight. At the same time, PE obtained over a δ-TiCl3 catalyst has a much (threefold) higher molecular weight. The introduction of hydrogen during polymerization for decreasing the molecular weight of PE is accompanied by a sharp drop in activity of the δ-TiCl3 catalyst, in distinction to the highly active supported TMC containing 3 wt. % Ti. Data about the effect of hydrogen content during polymerization on the molecular weight of PE were used to calculate the ratio of rate constants for polymer chain transfer with hydrogen (KtrH) and polymer chain propagation reaction (Кр). This value was close for TMCs of different composition containing magnesium dichloride. In the case of δ-TiCl3, the KtrHр value was approximately two times lower compared to TMCs.

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Main Subjects


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Articles in Press, Accepted Manuscript
Available Online from 02 November 2024
  • Receive Date: 11 October 2024
  • Revise Date: 02 November 2024
  • Accept Date: 02 November 2024
  • First Publish Date: 02 November 2024