Synthesis and Characterization of Novel Chromium Catalyst and Polyethylene with High Molecular Weight

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 (Mv ranging from 225800 to 637800 g·mol−1, 30≤Tp≤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.