Influence of propene pressure on the isotacticity of polypropene produced with typical C1‐symmetric metallocene and Ziegler‐Natta catalysts

Abstract Polymerization of propene was conducted at 40°C under reduced pressure (0.35 – 1.0 atm) using the C1‐Symmetric threo‐iPr(3‐tBuCp)(3‐tBuInd)ZrCl2/MAO and TiCl4/MgCl2/Al(iBu)3 catalyst systems and the effect of propene pressure on the microstructure of the resulting isotactic polypropene was investigated. In the case of C1‐symmetric metallocene, the [mmmm]‐pentad fraction decreased moderately with decreasing propene pressure, but the magnitude of decrease was much smaller than those reported by Busico et al. using typical C2‐symmetric metallocenes. Whereas, the [mmmm]‐pentad fraction of isotactic polypropene obtained with the conventional Ziegler‐Natta catalyst did not change so much in the pressure range. Thus, epimerization of the growing polymer chain was found to be drastically dependent upon the catalyst system.