Ethylene and 1-hexene have been copolymerized with the catalyst system 9-fluorenylidene-1-cyclopentadienylidene-2-hex-5-enylidene zirconium dichloride/PHT (PHT = partially hydrolyzed trimethylaluminum). The resultant polymer has been characterized. The product of the copolymerization parameters r(1) . r(2) indicates a statistical distribution of the monomers in the produced poly(ethylene-co-1-hexene). Various ansa-bis(fluorenylidene) and ansa-fluorenylidene cyclopentadienylidene zirconium dichloride complexes have also been used as catalyst precursors to homopolymerize ethylene and copolymerize ethylene and l-hexene heterogeneously. For these reactions, the relationships between "bite-angle", polymerization activity, and comonomer incorporation have been investigated using PHT/silica gel and MAO/silica gel as aluminoxane type cocatalysts. The effect of comonomer on the catalytic activity is generally positive for MAO/silica gel catalysts and negative for PHT/silica gel catalysts.