Activation and Stereospecific Control in Propylene Polymerization with MgCl2 Supported Ziegler-Natta Catalysts

In the isotactic polymerization of propene using MgCl2 supported Ziegler catalysts the addition of small amounts of a Lewis base to the cocatalytic solution causes a severe reduction of the activity of the aspecific sites, but enhances the activity of the isospecific sites; further addition of the same Lewis base cause moderate inhibition of all kinds of sites. These effects are observed with a variety of components of the cocatalytic solutions: both different alkylaluminiums and various aromatic esters or aromatic silanes. These results support the idea of alkylaluminium complexed with the Lewis base as major components of the isospecific sites.