Multistage process for the polymerization of ethylene

A slurry process for preparing an ethylene polymer comprising:

• a first polymerization stage comprising the step of:
• polymerizing ethylene in the presence of a solid catalyst system and a molecular weight regulator wherein the molecular weight regulator is present in a first molecular weight regulator concentration;
• and,
• a second polymerization stage comprising the step of:
• polymerizing ethylene in the presence of the solid catalyst system and the molecular weight regulator wherein the molecular weight regulator is present in a second molecular weight regulator concentration,
• wherein the first polymerization stage and the second polymerization stage are carried out
• (a) at a temperature in the range of from 60 to 120° C., and
• (b) the solid catalyst system comprises the product obtained by contacting:
• (A) a solid catalyst component comprising Ti, Mg, halogen, and
• (B) an organoaluminum compound
• wherein the solid catalyst system has:
• (i) a porosity (PF) of at least 0.3 cm3/g;
• and,
• (ii) a surface area lower than 100 m2/g as determined by BET method, and
• wherein the first molecular weight regulator concentration is different from the second molecular weight regulator concentration, and
• wherein the resulting ethylene polymer has a melt flow ratio F/P, according to ASTM 1238, of higher than 25.