Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO 2 /MgCl 2 (ethoxide type)/TiCl 4 /Di‐ n ‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

The bisupported Ziegler–Natta catalyst system SiO 2 /MgCl 2 (ethoxide type)/TiCl 4 /di‐ n ‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐ n ‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n ‐heptane from 45 to 70°C. The effects of the TEA and H 2 concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H 2 concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H 2 reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H 2 concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H 2 . Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003