Synthesis and characterization of novel chromium catalyst and polyethylene with high molecular weight

Abstract

Mononuclear carbon bridged cyclopentadienyl chromium complexes of the type [(C₅H₄) C (C₅H₁₀)CH₂(C₅H₄N)]CrCl₂(1), [(C₅H₄)C(CH₃)₂CH₂(C₅H₄N)]CrCl₂(2) and homodinuclear chromium complex of the type (CH₃)₂{[(C₅H₃)C(CH₃)₂CH₂(C₅H₄N)]CrCl₂}₂(3) were prepared by treatment of the lithium salts of cyclopentadiene ligands with pyridyl group with CrCl₃(THF)₃ in THF solution. All complexes were structurally characterized by mass spectra and elemental analysis. The structure of complex 1 was determined by X-ray diffraction analysis. Activated by MAO, complexes 1 and 2 are efficient catalysts in the polymerization of ethylene yielding polyethylene (BE) with a high molecular weight (M_v ranging from 225800 to 637800 g·mol⁻¹, 30≤T_p≤70°C under 0.9 MPa monomer pressure). High activities of polymerization are related to the unique electronic and steric structure of complexes 1 and 2. The melting points of the polymers determined by DSC and characterization data of¹³C NMR all show the synthesis of linear polyethylene (LPE) with a low branching extent.

Keywords

cyclopentadienylchromium / catalyst / ethylene polymerization / crystal structure

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