Staged reactor process

In a process for the in situ blending of polymers comprising contacting ethylene and one or more comonomers in two or more fluidized bed reactors connected in series, under polymerization conditions, with a catalyst system comprising (i) a supported or unsupported magnesium/titanium based precursor containing an electron donor and (ii) a hydrocarbyl aluminum cocatalyst in sufficient amount to complete the activation of the precursor, the improvement comprising:

• (A) increasing or decreasing the melt flow ratio and/or molecular weight of the blend by, respectively, decreasing or increasing the mole ratio of a precursor activator compound to the electron donor;
• or
• (B) increasing or decreasing the bulk density of the blend by, respectively, increasing or decreasing the mole ratio of a precursor activator compound to the electron donor with the following provisos:
• (I) the mole ratio of the precursor activator compound to the electron donor is in the range of about 0.1:1 to about 1:1;
• (II) the precursor activator compound can be one compound or a sequential mixture of two different compounds;
• (III) each precursor activator compound has the formula M(Rn)X(3−n) wherein M is Al or B;
• each X is independently chlorine, bromine, or iodine;
• each R is independently a saturated aliphatic hydrocarbon radical having 1 to 14 carbon atoms, provided that when M is Al, n is 1 to 3 and when M is B, n is 0 to 1.5;
• (IV) the activation of the precursor is carried out prior to the introduction of the precursor into the reactor;
• and
• (V) the activation in proviso (IV) is partial.