| 摘要 |
In a process comprising contacting ethylene per se or ethylene and one or mo re 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 in an amount sufficient to complete the activation of the precursor, the improvement comprising (A) mixing the precursor and the activator prior to introduction into the reactor in two or three steps, the last step being a topping-off step in which activation is completed; (B) maintaining the mixture from step (A) in slurry form; and (C) introducing the mixture from step (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 sequential mixture of two different compounds; (III) each activator compound has the formula A1(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; (IV) the activation of the precursor is essentially completed prior to the introduction of the precurso r into the reactor; and (V) no additional activator is introduced into the reactor(s). |
