High activity vanadium-based catalyst

In a catalyst system comprising:

• (A) a solid catalyst component consisting essentially of
• (1) a solid, particulate, porous inorganic carrier, as support for
• (2) the reaction product of (a) a vanadium trihalide and (b) an electron donor, and
• (3) a boron halide or alkyl-aluminum modifier,
• (B) a triethylaluminum cocatalyst, and
• (C) a halohydrocarbon polymerization promoter,
• the improvement wherein an ether activity enhancer is present in the catalyst system, said ether having the formula:
• R.sup.1 --O--R.sup.2
• wherein:
• R.sup.1 and R.sup.2 are independently monovalent hydrocarbon radicals free of aliphatic unsaturation containing from 1 to 20 carbon atoms, or together make up an aliphatic ring containing from 2 to 20 carbon atoms,
• said ether activity enhancer being present in an amount sufficient to provide a molar ratio of such either to the triethylaluminum cocatalyst of from 0.2:1 to 0.8:1.