| 摘要 |
A process comprising contacting ethylene and at least one alpha-olefin comonomer having 3 to 8 carbon atoms with a transition metal based catalyst system in two fluidized bed reactors connected in series, in the gas phase, under polymerization conditions, with the provisos that: (a) the first reactor is operated at a temperature at or above the dew point of the mixture of monomers, but no higher than about 5 degrees C. above said dew point; (b) 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; (c) other than the active catalyst referred to in proviso (b), no additional catalyst is introduced into the second reactor; (d) in the reactor in which a low melt index copolymer is made: (1) the alpha-olefin is present in a ratio of about 0.01 to about 0.4 mol of alpha-olefin per mol of ethylene; and (2) optionally, hydrogen is present in a ratio of about 0.001 to about 0.3 mol of hydrogen per mol of ethylene; and (e) in the reactor in which a high melt index polymer is made: (1) optionally, alpha-olefin is present in a ratio of about 0.005 to about 0.6 mol of alpha-olefin per mol of ethylene; and (2) optionally, hydrogen is present in a ratio of about 0.001 to about 3 mols of hydrogen per mol of ethylene.
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