| 摘要 |
A gas phase process for the production of an in situ polyethylene blend comprising contacting ethylene and at least one alpha-olefin comonomer having 3 to 8 carbon atoms with a magnesium/titanium based catalyst system including an activator and a cocatalyst in each of two fluidized bed reactors connected in series, under polymerization conditions, with the provisos that: (a) the mixture of ethylene copolymer matrix and active catalyst formed in the first reactor in the series is transferred to the second reactor in the series; (b) other than the active catalyst referred to in proviso (a) and the cocatalyst referred to in proviso (f), no additional catalyst is introduced into the second reactor; (c) in the first reactor in which a relatively high molecular weight copolymer is made: (1) the alpha-olefin is present in a ratio of about 0.01 to about 0.4 mole of alpha-olefin per mole of ethylene; and (2) optionally, hydrogen is present in a ratio of about 0.001 to about 0.3 moles of hydrogen per mole of ethylene; (d) in the second reactor in which a relatively low molecular weight copolymer is made: (1) the alpha-olefin is present in a ratio of about 0.01 to about 0.6 mole of alpha-olefin per mole of ethylene; and (2) hydrogen is present in a ratio of about 1 to about 2.5 moles of hydrogen per mole of ethylene; (e) a sufficient amount of one or more hydrocarbons is added to the first reactor or to the mixture formed in the first reactor prior to its introduction into the second reactor to provide about 0.5 to about 15 parts by weight of hydrocarbon(s) per 100 parts by weight of the in situ blend, each of said hydrocarbons being a saturated alicyclic hydrocarbon, which is liquid at process temperature, is non-polar, is essentially amorphous, and contains less than about 15 percent by weight paraffin wax; and (f) additional hydrocarbyl aluminum cocatalyst is introduced into the second reactor in an amount sufficient to restore the level of activity of the catalyst transferred from the first reactor to about the initial level of activity in the first reactor.
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