Homogeneous vanadium-based catalysts for the Ziegler–Natta polymerization of a-olefins

First published as an Advance Article on the web 12th September 2002 Although their activity is often inferior to that of other systems, the use of vanadium-based catalysts in homoge-neous Ziegler–Natta polymerizations allows the preparation of high-molecular-weight polymers with narrow molecular-weight distributions, ethene/a-olefin copolymers with high a-olefin incorporation, and syndiotactic polypropene. The main reason for the low activity of these catalysts is their deactivation during catalysis by reduction of active vana-dium species to low-valent, less active or inactive species. We here present an up-to-date review of this area with particular emphasis on the attempts to improve catalyst performance and stability by the use of additives or ancillary ligands.