Ethylene/propylene copolymer rubbers

A process comprising contacting ethylene, propylene, and, optionally, a diene, under polymerization conditions, with a catalyst system comprising:

• (A) a catalyst precursor comprising:
• (i) a vanadium compound, which is the reaction product of VCl.sub.3 and tetrahydrofuran;
• (ii) a modifier, which is diethylaluminum chloride or ethylaluminum sesquichloride;
• and
• (iii) a silica support for said vanadium compound and modifier,
• said catalyst precursor being in an independent or prepolymerized state,
• wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with oxygen or perchloropropene in an amount sufficient to increase the oxidation state of the vanadium by at least one;
• (B) as a cocatalyst, diethylaluminum chloride or a mixture of diethylaluminum chloride and triethylaluminum;
• and
• (C) optionally, as a promoter, ethyl trichloroacetate.

A process for the production of homogeneous polyethylene comprising contacting a mixture comprising ethylene and one or more alpha-olefins, under polymerization conditions, with a catalyst system comprising:

• (A) a catalyst precursor comprising:
• (i) a vanadium compound, which is the reaction product of
• (a) VX.sub.3 wherein each X is independently chlorine, bromine, or iodine;
• and
• (b) an electron donor, which is a liquid, organic Lewis base in which VX.sub.3 is soluble;
• (ii) a modifier having the formula BX.sub.3 or AlR.sub.(3-a) X.sub.a wherein each R is independently alkyl having 1 to 14 carbon atoms;
• each X is as defined above;
• and a is 1 or 2;
• and
• (iii) a support for said vanadium compound and modifier,
• said catalyst precursor being in an independent or prepolymerized state,
• wherein said independent catalyst precursor or said prepolymerized catalyst precursor have been pre-oxidized with an oxidant in an amount sufficient to increase the oxidation state of the vanadium by at least one;
• (B) a cocatalyst consisting essentially of a compound having the formula AlR.sub.(3-a) X.sub.a wherein R, X, and a are as defined above;
• and,
• (C) optionally, a promoter, which is a chlorinated ester having at least 2 chlorine atoms;
• a saturated or unsaturated aliphatic halocarbon having at least 3 carbon atoms and at least 6 halogen atoms;
• or a haloalkyl substituted aromatic hydrocarbon wherein the haloalkyl substituent has at least 3 halogen atoms.