Comparative study of propylene polymerization using monosupported and bisupported titanium‐based Ziegler–Natta catalysts

Heterogeneous Ziegler–Natta systems—MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate (DNBP)/triethylaluminum (TEA)/dimethoxymethylcyclohexylsilane (DMMCHS) and SiO₂/MgCl₂ (ethoxide type)/TiCl₄/DNBP/TEA/DMMCHS—were studied for the polymerization of propylene. The slurry polymerization of propylene was carried out with the catalyst systems in n‐heptane. Both systems performed with optimum activity at a particular Al]/DMMCHS]/Ti] molar ratio. The ratio to reach the highest activity was much lower for the bisupported catalyst system. The productivity of the bisupported catalyst was higher than that of the monosupported one. Polypropylene of a high isotacticity index (II; >96%) was obtained with both systems and did not significantly change with an increasing Al]/DMMCHS]/Ti] molar ratio. The addition of hydrogen as a chain‐transfer agent reduced II of the polymers obtained with both systems. The effect of the polymerization temperature (40–75°C) on the viscosity‐average molecular weight (M_v) and II showed a decrease in both cases. The bisupported catalyst system produced a polymer with higher M_v. The effect of temperature on II was similar for both the monosupported and bisupported systems. A monomer pressure of 2.02 × 10⁵ to 0.8 × 10⁶ Pa increased M_v of the obtained polymer. II of the polymer slightly decreased with increasing monomer pressure. The titanium content of the catalyst was 1.70 and 3.55% for the monosupported and bisupported systems, respectively. The surface area of the bisupported catalyst was higher than that of the monosupported catalyst. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2220–2226, 2006