| abstract |
A process is provided for producing a bimodal ethylene polymer blend comprising contacting in a first gas phase, fluidized bed reaction zone under polymerization conditions, a gaseous monomeric composition comprising a major proportion of ethylene and, optionally, hydrogen, with a non-prereduced supported titanium/magnesium precursor catalyst as primary catalyst component in combination with a hydrocarbyl aluminium reducing co-catalyst, the hydrogen/ethylene molar ratio (H₂/C₂ ratio) being no higher than about 0.3 and the ethylene partial pressure being no higher than about 100 psia, to produce a relatively high molecular weight (HMW) polymer associated with catalyst particles, transferring the HMW/catalyst particles to a second gas phase, fluidized bed reaction zone into which is also fed hydrogen and a gaseous monomeric composition comprising a major proportion of ethylene, under polymerization conditions including an H₂/C₂ ratio of at least about 0.9 and at least about 8.0 times that in the first reaction zone, and an ethylene partial pressure of at least 1.7 times that in said first reaction zone, to produce a low molecular weight (LMW) polymer deposited on and within the voids of the HMW polymer/catalyst particles, the resulting bimodal polymer blend obtained from the second reaction zone having a fraction of HMW polymer of at least about 0.35. |