A catalyst composition for polymerizing olefins to polymers having bimodal molecular weight distribution comprises two transition metal-containing metallocene compounds, a magnesium compound, an alcohol, an aluminum containing co-catalyst and a polymeric support. The transition metal in one of the metallocene compounds is zirconium and the transition metal in the second metallocene compound is selected from the group consisting of titanium, vanadium and hafnium. Polyolefin polymers made using the catalyst composition have broad molecular weight distributions and are useful in film and blow molding applications.