Polymerization of olefins in the presence of catalyst prepared from organo zirconium-chromium mixtures

A process for polymerizing one or more .alpha.-olefins which comprises conducting said polymerization under Ziegler polymerization conditions in the presence of a catalyst which comprises

• (A) at least one member of the group consisting of
• (1) at least one zirconium compound, represented by the empirical formula ##STR3## wherein R is a hydrocarbon group having from 1 to about 12 carbon atoms;
• (2) at least one hydrocarbon soluble chromium compound represented by the empirical formula ##STR4## wherein R is a hydrocarbon group having from 1 to about 12 carbon atoms and a has a value equal to the valence of Cr;
• and
• (3) a mixture of components (1) and (2) in a mole ratio of component (2) to component (1) of from about 0.05:1 to about 10:1;
• (B) a solid catalyst support containing magnesium prepared by reacting (a) a compound represented by the empirical formula MgR".sub.2.xAlR".sub.3 wherein each R" is independently a hydrocarbyl or hydrocarbyloxy group having from 1 to about 20 carbon atoms and x has a value from about zero to about 10 with (b) a halide source selected from non-metallic halides and metallic halides;
• (C) a tetrahydrocarbyloxy titanium or titanium halide compound;
• and
• (D) an organometallic activating agent;
• wherein the Mg:(Cr+Zr) atomic ratio is from about 1:1 to about 100:1;
• the Al:(Cr+Zr) atomic ratio is from about 1:1 to about 200:1;
• the (Cr+Zr):Ti atomic ratio is from about 0.5:1 to about 20:1;
• and the excess X:Al atomic ratio is from about 0.0005:1 to about 5:1.