PROPYLENE POLYMERIZATION WITH UNBRIDGED METALLOCENES - LIGAND EFFECTSON THE SELECTIVITY FOR ELASTOMERIC POLYPROPYLENE

Bis(2-arylindenyl)zirconium dichlorides activated by methylaluminoxane produce elastomeric polypropylene with a stereoblock microstructure. In an effort to experimentally explore the importance of the 2-arylind ene ligand in producing these materials, a series of catalysts was inv estigated that differed significantly from the parent ligand architect ure. In particular, we sought to examine the influence of ligand aryl stacking on the polymerization behavior of these metallocenes. We disc overed that the bis(2-arylindenyl) framework is important for the prod uction of elastomeric polypropylene by this type of unbridged complex. Small changes in the fundamental catalyst structure upset the delicat e balance between ligand rotation and monomer insertion resulting in,t he production of amorphous polymers.