Syndiotactic polymerization of propylene: Single-site vanadium catalysts in comparison with zirconium and nickel

The syndiotactic-specific polymerization of propylene can be promoted by si ngle-site catalysts based on vanadium, nickel and group IV metals. The poly merization mechanisms are reasonably well established for nickel and group IV metals. The polymerization mechanisms are reasonably well established fo r nickel and group IV metals. For vanadium catalysts the polymerization mec hanisms reported in the literature are still debatable, since the stereoche mistry of the monomer insertion is well known, but the active species have never been isolated. In this paper the mechanisms concerning Ni and group I V metal catalysts are briefly summarized and proposed mechanisms concerning vanadium are compared within one another.