Abstract—A series of zirconium catalysts based on tridentate 8-hydroxyquinoline Schiff base ligands were prepared and successfully used for polymerization of ethylene. The highest activities of the prepared catalysts were obtained at polymerization temperatures about 30–45ºC. By increasing the [Al]/[Zr] molar ratio productivity of all the catalysts enhanced to an maximum value then decrease at higher [Al]/[Zr] molar ratio with the exception of catalyst 4, which showed no optimum activity in the range studied. Also, the activities and selectivities to produce low-carbon olefins were profoundly influenced by the catalysts structure indicating the dramatic effects of the substitution on the polymerizations behavior. Fouling of the reactor was strongly related to polymerization parameters like as monomer pressure and [Al]/[Zr] ratio in the homogeneous polymerization. Heterogeneous polymerization of ethylene using the catalysts and the MAO modified silica decreased the fouling. The obtained polyethylenes have a melting point of about 125–130°C, crystallinities of about 45–55% and PDI of 2.45–3.45.

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