Control of stereoerror formation with high-activity 'dual-side' zirconocene catalysts: A novel strategy to design the properties of thermoplastic elastic polypropenes

The new C₁-symmetric complexes rac-[1-(9-η⁵-fluorenyl)-2-(2- methylbenz[e]-1-η⁵-indenyl)ethane]zirconium dichloride (14a), rac-[1-(9- η⁵-fluorenyl)-2-(4,5-cyclohexa-2-methyl-1-η⁵-indenyl)ethane]zirconium dichloride (14b), and rac-[1-(9-η⁵-fluorenyl)-2-(5,6-cyclopenta-2-methyl- 1-η⁵-indenyl)ethane]zirconium dichloride (15) were prepared in up to 93% yield. These compounds, activated with methyl aluminoxane, exhibit high active propene polymerization rates which remain constant over hours, even at elevated polymerization temperatures of 50 and 70 °C. The two different coordination sites of these 'dual-side' catalysts lead to isotactic polypropenes with variable amounts of stereoerrors, depending on the monomer concentration. The 2-methyl substituent of the indenyl ligands results, at the same time, in significantly increased molecular weights of the polymer products (up to 2.3 x 10⁵ g mol^-1), the bulk properties of which can be adjusted from flexible, semicrystalline thermoplastic to excellent thermoplastic elastic.