Catalyst system for the polymerization of olefins

A catalyst system for the polymerization and copolymerization of olefins, said system comprising:

• (a) a conventional Ziegler-Natta catalyst component wherein the conventional Ziegler-Natta catalyst component comprises:
• a solid catalyst component prepared by:
• (i) suspending a dialkoxy magnesium in an aromatic hydrocarbon that is liquid of normal temperatures, (ii) contacting the dialkoxy magnesium with a titanium halide and further contacting the resulting composition a second time with the titanium halide, and (iii) contacting the dialkoxy magnesium with a diester of an aromatic dicarboxylic acid at some point during the treatment with the titanium halide in (ii);
• and
• (b) an electron donor described by the formula:
• ##STR6## wherein R.sub.1 is an alkyl or cycloalkyl group of 3 or 5 carbon atoms having mirror image symmetry containing a secondary carbon atom attached to the silicon atom;
• R.sub.2 and R.sub.3 are each independently an alkyl or aryl group;
• and R.sub.4 is an alkyl or cycloalkyl group of 1-6 carbon atoms having mirror image symmetry with a secondary carbon atom attached to the silicon atom;
• and
• (c) an organoaluminum compound;
• said system being characterized by:
• (i) a catalyst efficiency of over 30 kilograms of polymer product per gram of catalyst in one hour as the mole ratio Si/Ti as derived from the Si in compound (b) to the Ti from compound (a) is within the range of 4-200.