Synthesizing UHMWPE using Ziegler-Natta catalyst system of MgCl_2(ethoxide type)/TiCl_4/tri-isobutylaluminum

摘要

A Ziegler-Natta catalyst of MgCl_2 (ethoxide type)/TiCl_4 has been synthesized. In order to obtain ultra high molecular weight polyethylene (UHMWPE) triisobutylaluminum 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 investigated. The results showed increasing [Al]/[Ti] ratio in the range of 78-117, decreased the Mv of the obtained polymer from 7.8 × 10~6 to 3.7 × 10~6 however, further increase of the ratio, resulted in decreased of by much slower rate up to [Al]/[Ti] = 588. 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°C decreased the Mv from 9.3 × 10~6 to 3.7 × 10~6. 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°C increased the productivity of the catalyst however, further increase in the temperature up to the 90°C 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 × 10~6 to 9 × 10~6 was feasible.