New C1-Symmetric Metallocenes for the Polymerization of Olefins

For the polymerization of propene in solution three new C₁-symmetric metallocenes, (I) (Me₂C(PhCp)(Flu)]ZrCl₂, (II) [Me₂C(cHCp)- (Flu)]ZrCl₂, and (III) [PhMe₃PenFlu)]ZrCl₂, were compared. The zirconocene (III) is more stereorigid than (I) and (II) and, therefore, has special properties. At a polymerization temperature of 30 °C, (I) in combination with MAO exhibits the highest activity of 7500 kg PP/(mol Zrh*c_p), which is about 5 times higher than the unsubstituted [Me₂C(Cp)(Flu)]ZrCl₂ catalyst. At 60 °C however, compound (III) is much more active than the others due to the higher thermal stability. A strong dependence of the activity on the propene concentration is observed with all catalysts. The high molecular weight of the polypropene produced by (III) is of particular interest; it is two to four times higher than that of polymers synthesized with the other C₁-symmetric zirconocenes. All three catalysts produce polymers with a hemiisotactic microstructure. (III) affords a polymer with more isotactic blocks while polymer produced by (I) has more syndiotactic blocks.