Multistage process for producing ethylene polymer compositions

A process of producing an ethylene polymer composition in multiple stages, said process comprising polymerizing ethylene, alone, or with a comonomer, to produce an ethylene polymer in a first stage, transferring the polymer produced in the first stage into a second stage, in which a second stage ethylene is polymerized, alone, or with a comonomer, in the presence of the polymer produced in the first stage, and wherein the first stage is a slurry polymerization stage, and the polymerization in the first stage is carried out in the presence of a catalyst system comprising:

• (a) a solid catalyst precursor comprising a transition metal selected from titanium and vanadium;
• magnesium, a halide, an electron donor, and a solid particulate material comprising an inorganic oxide, and (b) an organoaluminium compound;
• and
• wherein the median particle diameter of the solid catalyst precursor, based upon the total volume of solid catalyst precursor, D50, is from 4 to 9 micrometers.