Ethylene polymerization by 3-oxa-pentamethylene bridged dinuclear metallocene (Ti, Zr)/MAO systems

Two hetero-atom containing bridged dinuclear metallocene complexes, (CpMCl₂)₂(C₅H₄CH₂CH₂OCH₂CH₂C₅H₄) M = Ti (1), Zr (2)], have been synthesized by treating the disodium salt of the corresponding ligand (C₅H₅CH₂CH₂)₂O with two equivalents of CpTiCl₃ and CpZrCl₃ · DME, respectively, in THF at 0 °C and characterized by ¹H- and ¹³C-NMR, MS and IR spectroscopy. Homogenous ethylene polymerization by those complexes has been conducted systematically in the presence of methylaluminoxane (MAO). The influences of reaction parameters, such as MAO]/Cat] molar ratio, catalyst concentration, ethylene pressure, temperature and time, have been studied in detail. The catalytic activities of the dinuclear complexes 1 and 2 were higher than those of (MeCpTiCl₂)₂(C₅H₄CH₂C₆H₄CH₂C₅H₄) (3), (CpZrCl₂)₂(C₅H₄CH₂C₆H₄CH₂C₅H₄) (4) and the mononuclear metallocenes Cp₂TiCl₂ and Cp₂ZrCl₂, respectively. Complex 2 showed high catalytic activity at high temperature (50-100 °C) and high pressure (6 bar). The molecular weight distributions of polyethylene produced by 1 and 2 (MWD = 2.49 and 5.90) were broader than those using the corresponding mononuclear metallocenes (MWD = 2.05 and 2.15). The melting points of the polyethylene produced ranged from 129 to 133 °C, indicating a high linearity and a high crystallinity.