A process to produce a first catalyst composition is provided. The process comprises contacting at least one first organometal compound, oxygen bridged mono-cyclopentadienyl transition metal dimer, and at least one activator to produce the first catalyst composition. The activator is selected from the group consisting of aluminoxanes, fluoro-organo borates, and treated solid oxide components in combination with at least one organoaluminum compound. In another embodiment of this invention, a process to produce a second catalyst composition for producing bimodal polymers is provided. The process comprises contacting at least one first organometal compound, at least one activator, and at least one second organometal compound to produce the second catalyst composition. The first and second catalyst compositions are also provided as well as polymerization processes using these compositions to produce polymers.