Image Number 6 for United States Patent #5589556.
Catalyst and process for the stereospecific propagation of a polymer chain derived from an ethylenically unsaturated monomer which contains 3 or more carbon atoms or is substituted vinyl compound. The catalysts comprise stereorigid metallocenes in which a structural bridge is not required for stereorigidity. The ring structures of the metallocene catalyst are substituted cyclopentadienyl rings. The substituent groups on the cyclopentadienyi rings impart stereorigidity to the catalyst by virtue of a sterically hindered relationship between the rings sufficient to prevent rotation of the rings. The catalyst is contacted with a C.sub.3 + alpha olefin or other ethylenically unsaturated compound in a polymerization reaction zone and maintained in contact with the catalyst in the reaction zone under polymerization conditions to produce a stereospecific polymer.