Modification of Ziegler-Natta catalysts by cyclopentiadienyl-type ligands: Activation of titanium-based catalysts

Conventional Ziegler-Natta catalysts, based on TiCl4 supported on MgCl2, were modified by substituting a part of the chlorides by cyclopentadienyl (and derivatives) ligands. Although these catalysts are very active (activities up to 105 g PE/g catalyst/h) they exhibit a conventional Ziegler-Natta behavior (methylaluminoxane is not necessary, polyethylene produced with a rather broad molar weight distribution, low sensitivity to hydrogen). It was attributed to cluster effects: an increase of the number of conventional TiCl4 active sites by adding cyclopentadienyl ligands on titanium neighbors.