Patent ID: 7563851

Claim:
A process for producing an ethylene polymer comprising the steps of: contacting ethylene under polymerization conditions with a catalyst system in a reactor, said catalyst system comprising a supported chromium catalyst comprising chromium oxide, an alkyl aluminum alkoxide or an alkyl aluminum alkoxide in combination with an alkyl aluminum, and a silica-containing support comprising silica selected from the group consisting of silica having: (a) a pore volume of about 1.1 to about 1.8 cm 3 /g and a surface area of about 245 to about 375 m 2 /g, (b) a pore volume of about 2.4 to about 3.7 cm 3 /g and a surface area of about 410 to about 620 m 2 /g, and (c) a pore volume of about 0.9 to about 1.4 cm 3 /g and a surface area of about 390 to about 590 m 2 /g; b) wherein the supported chromium catalyst is activated at about 400 to about 860° C.; and c) wherein at least a portion of the alkyl aluminum alkoxide or the alkyl aluminum oxide in combination with the alkyl aluminum is added in situ, such that the portion of the alkyl aluminum alkoxide or the alkyl aluminum oxide in combination with the alkyl aluminum is added into the reactor in the presence of the monomers under polymerization conditions, and is not combined with the supported chromium catalyst prior to the addition into the reactor; wherein the alkyl aluminum oxide is present in an amount such that the polymer side chain branching, of the resulting ethylene polymer is reduced as compared to an ethylene polymer produced under identical conditions in the absence of the alkyl aluminum alkoxide, and wherein the alkyl aluminum alkoxide is present in an amount to effect a final molar ratio of aluminum to chromium of from about 0.1:1 to 10:1.