Ethylene-propylene block copolymerization process and product

A continuous sequential vapor phase block copolymerization process for the production of impact resistant ethylenepropylene polymers at high productivity rates, which comprises:

• (A) providing a preformed propylene polymer in finely divided form, said preformed polymer containing active catalyst residues and having been prepared by polymerizing propylene in the presence of a catalyst composition containing the components
• (a) an aluminum trialkyl or an aluminum trialkyl at least partially complexed with an electron donor compound, and
• (b) titanium tri- or tetrahalide supported on magnesium dihalide, or a complex of a titanium tri- or tetrahalide with an electron donor compound supported on magnesium dihalide, the components (a) and (b) being provided in a molar ratio of Al/Ti between about 10 and about 200;
• (B) introducing said preformed polymer, ethylene and propylene into at least one continuously agitated reaction zone,
• (C) introducing an additional quantity of component (a) to said reaction zone, said quantity ranging from about 5 to about 50% of the quantity in the preparation of the prepolymer;
• and
• (D) polymerizing said ethylene and propylene monomers in the vapor phase in the reaction zone onto said preformed propylene prepolymer.