Process for the in situ blending of polymers

Claim 1

A process for the in situ blending of polymers wherein a higher density ethylene copolymer matrix is prepared in a high melt index reactor and a lower density ethylene copolymer is then incorporated into the ethylene copolymer matrix in a low melt index reactor comprising continuously contacting, under polymerization conditions, a mixture of ethylene and one alpha-olefin having 4 or 6 carbon atoms with a catalyst in two fluidized bed reactors connected in series, said catalyst comprising: (i) a silica supported complex consisting essentially of magnesium, titanium, halogen, an electron donor, and at least one activator compound having the formula AlR' e X' f H g wherein X' is Cl or OR'"; R" and R'" are saturated aliphatic hydrocarbon radicals having 1 to 14 carbon atoms and are the same or different; f is 0 to 1.5; g is 0 or 1; and e+f+g=3; and (ii) a hydrocarbyl aluminum cocatalyst, the polymerization conditions being such that an ethylene copolymer matrix having a melt index in the range of about 122 to about 600 grams per 10 minutes is formed in the high melt index reactor and a lower density ethylene copolymer having a melt index in the range of about 0.1 to about 1 gram per 10 minutes is formed in the low melt index reactor, each copolymer having a density of about 0.860 to about 0.965 gram per cubic centimeter and a melt flow ratio in the range of about 22 to about 70, and being admixed with active catalyst, with the provisos that: (a) the mixture of ethylene copolymer matrix and active catalyst formed in the high melt index reactor is transferred to the low melt index reactor; (b) other than the active catalyst referred to in proviso (a) and the cocatalyst referred to in proviso (e), no additional catalyst is introduced into the low melt index reactor; (c) in the high melt index reactor: (1) the alpha-olefin is present in a ratio of about 0.1 to about 3.5 moles of alpha-olefin per mole of ethylene; and (2) hydrogen is present in a ratio of about 0.5 to about 2 moles of hydrogen per mole of combined ethylene and alpha-olefin; (d) in the low melt index reactor: (1) the alpha-olefin is present in a ratio of about 0.1 to about 3.5 moles of alpha-olefin per mole of ethylene; and (2) hydrogen is present in a ratio of about 0.01 to about 0.3 mole of hydrogen per mole of combined ethylene and alpha-olefin; and (e) additional hydrocarbyl aluminum cocatalyst is introduced into the low melt index reactor in an amount sufficient to restore the level of activity of the catalyst transferred from the high melt index reactor to about the initial level of activity in the high melt index reactor.