Patent ID: 6982304

Claim:
A process to produce an ethylene polymer, the process comprising the steps of: blending at least one chromium oxide catalyst carried on a first support, the chromium oxide catalyst including compounds calcinable to chromium oxide at conditions used to activate the chromium oxide catalyst, and at least one silyl chromium catalyst carried on a second support to form a catalyst mixture, wherein the chromium oxide catalyst is present in an amount from about 25 to about 50 weight percent based on the total weight of the catalyst mixture and the silyl chromium catalyst is present in an amount of about 50 to about 75 weight percent based on the total weight of the catalyst mixture; introducing the catalyst mixture into a polymerization reactor, wherein at least one monomer comprising ethylene is present in the reactor and the reactor is maintained at polymerization conditions such that the at least one monomer will polymerize in the presence of the catalyst mixture; activating the chromium oxide catalyst either before or after the blending step but prior to introducing the catalyst mixture into the reactor; and, contacting the catalyst mixture and the at least one monomer in the reactor such that an ethylene polymer is formed, wherein the ethylene polymer is characterized, in comparison to an ethylene polymer prepared under the same polymerization conditions in the presence of the chromium oxide catalyst only, by an increase in environmental stress crack resistance (ESCR) at least about 400% and an increase in swell of no more than about 15%.