Process for the preparation of polyethylene

A process comprising contacting ethylene or ethylene and one or more comonomers in one or more fluidized bed reactors, under polymerization conditions, with a catalyst system comprising (i) a supported or unsupported magnesium/titanium based precursor in slurry form, said precursor containing an electron donor;

• and (ii) an activator containing aluminum in an amount sufficient to essentially complete the activation of the precursor, the method comprising:
• A) mixing the precursor and a portion of the activator prior to introduction into the reactor in at least one mixing procedure to prepare a partially activated precursor;
• B) mixing the partially activated precursor with the remainder of the activator to essentially complete the activation of the precursor and to prepare an essentially completely activated precursor;
• C) maintaining the mixture from (A) in slurry form;
• and
• D) introducing the mixture from (B) into the reactor with the following provisos:
• (i) the atomic ratio of aluminum to titanium is in the range of about 1:1 to about 15:1, and the mole ratio of activator to electron donor is about 1:1 to about 2:1;
• (ii) the activator is one compound or a mixture of two different compounds;
• (iii) each activator compound has the formula Al(Rn)X(3−n) wherein each R is independently a saturated aliphatic hydrocarbon radical having 1 to 14 carbon atoms;
• each X is independently chlorine, bromine, or iodine;
• and n is 1 to 3;
• and
• (iv) no additional activator is introduced into the reactor(s).