Block copolymerization process

A continuous sequential vapor phase block copolymerization process for the production of impact resistant ethylene-propylene 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 at least partially complexed with an aromatic acid ester electron donor compound wherein the aluminum trialkyl is one containing from 1 to 8 carbon atoms in the alkyl groups and the molar ratio of trialkyl aluminum to electron donor ranges between 2 and about 5, and
• (b) a complex of a titanium tri- or tetrahalide with an aromatic acid ester electron donor compound supported on magnesium dihalide wherein the titanium content of component (b) is about 1 and about 3 weight percent,
• wherein catalyst components (a) and (b) are provided to the reaction zone in a molar ratio of Al/Ti of between about 10 and about 200;
• (B) introducing said preformed polymer into at least one continuously agitated reaction zone;
• (C) introducing ethylene and propylene monomers to said reaction zone in a molar ratio of ethylene to propylene of from about 0.15 to about 0.3;
• (D) polymerizing said ethylene and propylene monomers in the vapor phase in the reaction zone onto said preformed propylene prepolymer at a temperature of from about 50.degree. F. to about 210.degree. F.