Ethylene polymerization catalyzed by using two-component metallocene catalysts

Polyethylene with broad molecular weight distribution can be obtained by using catalytic systems consisting of two or more catalyst, components. An asymmetrically bridged metallocene compound [(CH3)(2)C(eta-C5H4)(eta-C9H6)]ZrCl2 and different unbridged metallocene compounds (Cp)(2)ZrCl2, (Cp)(2)ZrCl2 and (Cp)(2)ZrCl2 were used to constitute three catalytic systems cocatalyied with MAO for ethylene polymerization. Polyethylene with short chain branch and broad molecular weight distribution was obtained. By changing the molar ratio of two-component metallocene catalysts and polymerization temperature, the activity of the ethylene polymerization and the molecular weight and molecular weight distribution of the resultant polyethylene were investigated. The molecular weight and molecular weight distribution of polyethylene were determined by viscometry and GPC. The melt point and crystallinity of polyethylene samples were determined by DSC. The results showed that the molar ratio and polymerization temperature had important effect on the activity and molecular weight. The results indicated that it was possible to tailor molecular weight and molecular weight distribution by changing the molar ratio of the two-component metallocene catalysts and polymerization temperature in ethylene polymerization with two-component metallocene catalyst systems.