Olefin polymerization catalyst systems and methods for making the same

Borate activated catalyst systems and methods for making the same for gas phase or slurry phase olefin polymerization are provided. The catalyst system can include a first catalyst comprising a borate activated mono cyclopentadienyl metallocene compound and a second catalyst comprising a supported bis cyclopentadienyl metallocene complex. A supported bis cyclopentadienyl metallocene complex can be prepared to provide a preformed, supported catalyst, wherein the supported bis cyclopentadienyl metallocene complex comprises bis(1,3-methylbutyl cyclopentadienyl) zirconium dichloride. The preformed, supported catalyst can be mixed with mineral oil or hydrocarbon solvent to form a slurry. The slurry can be mixed with a borate activated mono cyclopentadienyl metallocene compound to form the borate activated catalyst system.