Abstract Two FI-type catalysts of Bis[N-(3,5-dicumylsalicylidene)- naphthylaminato]zirconium(IV) dichloride (catalyst (a)) and Bis[N-(3,5-dicumylsalicylidene)-anthracylaminato] zirconium(IV) dichloride (catalyst (b)) were prepared and used for ethylene polymerization comparatively. Methylaluminoxane (MAO) was used as cocatalyst. Polymerization reactions of ethylene using the prepared catalysts at the different conditions of polymerization were carried out. Plurality of the fused aromatic rings on the N atom of the imine in the catalyst structure affected the polymerization activity andmolecular weight of the resulting polymer as well. Productivity of the prepared catalysts increased with the addition of [Al]/[Zr] molar ratio. The highest activity was observed at about 35–40 °C for the catalysts. The catalyst (b) produced higher viscosity average molecular weight (Mv) of the obtained polyethylene, while generally the activity of the catalyst (a) was higher than the catalyst (b). Similar behavior was observed for the polymerization carried out at the monomer pressure of 2 to 6 bars using the catalysts. The higher the pressure the more activity of the catalysts obtained, in the range studied. Crystallinity and melting point of the obtained polymer were between 55–65% and 120–135 °C respectively. Higher pressure increased both the crystallinity and the Mv values of the resulting polymer. The polymerization was carried out using different amounts of hydrogen. Higher amount of hydrogen could increase the activity of the catalysts. A linear dependence between the polymerization time and the molar weight was observed, however the polydispersity was broadened with the time.

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