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.