Zirconium and Hafnium Complexes Bearing Salen Ligands for the Polymerization of Ethylene

A series of previously synthesized homoleptic and heteroleptic complexes of zirconium and hafnium were used for the polymerization of ethylene. Upon activation with methylaluminoxane, all the complexes serve as pre-catalysts for the polymerization of ethylene. The effects of polymerization time, reaction temperature, solvents, and methylaluminoxane to catalyst ratio on the polyethylene yield were investigated. The catalyst activity depends on the coordination environment of the metals. The highest activity obtained was 5.91 × 104 g of polyethylene/[(mol of catalyst) h] under the optimized conditions of hexane as a solvent, reaction time and temperature of 30 min and 50°C respectively, and MAO to catalyst ratio of 1000 : 1.