Summery: A Ziegler-Natta catalyst of MgCl2 (ethoxide type)/TiCl4 has been synthes- ized. In order to obtain ultra high molecular weight polyethylene (UHMWPE) tri- isobutylaluminum which is less active to chain transfer was used as cocatalyst. Slurry polymerization was carried out for the polymerization of ethylene while, dilute solution viscometry was performed for the viscosity average molecular weight (Mv) measurement. The effect of [Al]/[Ti] molar ratio, temperature, monomer pressure and polymerization time on the Mv and productivity of the catalyst have been inves- tigated. The results showed increasing [Al]/[Ti] ratio in the range of 78–117, decreased the Mv of the obtained polymer from 7.8
106 to 3.7
106 however, further increase of the ratio, resulted in decreased of by much slower rate up to [Al]/[Ti]¼588. The higher pressure in the range of 1–7 bars showed the higher the Mv of the polymer obtained, while increasing temperature in the range of 50 to 90 8C decreased the Mv from 9.3
106 to 3.7
106 . The Mv rapidly increase with polymerization time in the first 15 minutes of the reaction, this increase was slowly up to the end of the reaction (120 min). Increasing [Al]/[Ti] ratio raised productivity of the catalyst in the range studied. Rising reaction temperature from 50 to 75 8C increased the productivity of the catalyst however, further increase in the temperature up to the 90 8C decreased activity of the catalyst. Monomer pressure in the range 1 to 7 bars yields higher productivity of the catalyst. Also by varying polymerization conditions synthesizing of UHMWPE with Mv in the range of 3
106 to 9
106 was feasible.

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