Ethylene polymerization by novel 4,4′-bis(methylene)biphenylene bridged homodinuclear titanocene and zirconocene combined with MAO

Abstract

4,4′-Bis(methylene)biphenylene bridged homodinuclear titanocene ( 3) and zirconocene ( 4) have been synthesized by treatment of CpTiCl 3 and CpZrCl 3 · DME with Na 2[C 5H 4CH 2C 6H 4- p-C 6H 4CH 2C 5H 4], 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 Cp 2TiCl 2/MAO and Cp 2ZrCl 2/MAO, respectively. However, the catalytic activity of 3 is nearly half as high as that of 4, which reached 1.31 × 10 6 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.