Add time:09/24/2019         Source:sciencedirect.com

4,4′-Bis(methylene)biphenylene bridged homodinuclear titanocene (3) and zirconocene (4) have been synthesized by treatment of CpTiCl3 and CpZrCl3 · DME with Na2[C5H4CH2C6H4-p-C6H4CH2C5H4], respectively, in THF and characterized by 1H NMR and element analysis. After activation with methyl aluminoxane (MAO), these catalysts were used for the homogeneous polymerization of ethylene. The influences of reaction conditions, such as temperature, time, catalyst concentration and molar ratio of MAO/Cat. on ethylene polymerization were investigated in detail. The catalytic activities of 3 and 4 are more than three times higher than that of the phenyldimethylene bridged homodinuclear metallocene of titanocene (5) and zirconocene (6), respectively, and also twice higher than that of Cp2TiCl2/MAO and Cp2ZrCl2/MAO, respectively. However, the catalytic activity of 3 is nearly half as high as that of 4, which reached 1.31 × 106 g PE/mol cat h. The molecular weight of polyethylene increases simultaneously with prolongation of polymerization time. GPC spectra show that 3 and 4 produce polyethylene with broad molecular weight distribution (4.28 and 3.18). The high melting points of the products (131–134 °C) indicate that the polyethylene formed is highly linear and highly crystalline.

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