Copolymerization catalyst and process for polymerizing impact resistant ethylene-propylene polymers

Claim 1

In the process for preparing impact resistant ethylene-propylene polymers having high impact properties combined with high stiffness, which process comprises: (a) preparing a propylene prepolymer by polymerizing propylene in a first liquid phase reaction zone in the presence of a first catalyst system comprising: (i) a highly active solid catalyst component comprising titanium tetrachloride, magnesium chloride, and an electron donor, (ii) as cocatalyst a compound AlR 3 where R represents an alkyl group of from 2 to 8 carbon atoms, and (iii) a selectivity control agent which may be partly or totally complexed with the co-catalyst; (b) separating the propylene prepolymer from volatile constituents; and (c) introducing said separated propylene prepolymer, ethylene monomer and propylene monomer into at least one vapor phase reaction zone; the improvement wherein a second catalyst system is introduced into said vapor phase reaction zone, said second catalyst system comprising the solution prepared by: (i) polymerizing a C 5 -C 9 alpha-monoolefin in a second liquid phase reaction zone in the presence of a second catalyst system selected from the group consisting of: (i) a MgCl 2 supported-type catalyst system comprising a highly active solid catalyst component comprising titanium tetrachloride, magnesium chloride, and an electron donor, and as cocatalyst a compound AlR 1 3 where R 1 represents an alkyl group of from 2 to 8 carbon atoms; and (ii) a Ziegler/Natta-type catalyst system comprising an active TiCl 3 catalyst component and an organo-aluminum compound of the formula AlR 2 n X 3-n where R 2 is an alkyl group of 2 to 12 carbon atoms, X is hydrogen or halogen and n has a value of from 0.1 to 3; and a diluent, wherein said diluent is selected such that the resulting polymer is soluble therein and wherein the amount of C 5 -C 9 alpha-monoolefin polymerized therein is about 0.05 to about 100 grams per gram of second catalyst system; and (ii) recovering the resultant catalyst-diluent-polymer mass.