A new class of thermoplastic elastic polypropenes prepared with a high activity "dual-side" zirconocene catalyst

It is well known that the mechanical properties of highly isotactic polypropene depend on the crystalline structure of the material. Up to now, the polymer properties were modified by varying either the processing conditions - e.g., extrusion, annealing etc. - or the composition - e.g., blending, nucleation. Highly active ethylene bridged C₁-symmetric zirconocene catalysts can be used to design the material properties by varying the crystallinity of thermoplastic (elastic) polypropenes. With the new unsymmetric catalyst rac-dichloro[1-(9-fluorenyl)-2-(R, S)-(5,6-cyclopenta-2-methylinden-1-η⁵-yl)ethane]zirconium (IV)/MAO (1) polypropenes of variable isotacticities are accessible. The variable and thus defined use of two different sides of the catalytically active species allows the placement of single, cumulated and consecutive [rr]-triads within an isotactic polymer chain. The formation of these stereoerrors is adjusted in an arbitrary manner by the polymerization conditions temperature and monomer concentration. The mechanical properties of polypropenes produced with 1/MAO vary from tough thermoplastic to excellent elastic. Stress-strain behavior of these physically crosslinked elastomers can be designed similar to the ones of polyisoprene or partly crosslinked natural rubber.