This paper describes the synthesis of poly(ethylene-co-1,4-hexadiene) copolymers, which are useful intermediates for the preparation of functionalized linear low-density polyethylene (LLDPE-f). Three catalyst systems, including one heterogeneous catalyst (TiCl3.AA/Et(2)AlCl) and two homogeneous metallocene catalysts (Cp(2)ZrCl(2) and Et(Ind)(2)ZrCl2 with MAO), were used in the copolymerization reaction between ethylene and 1,4-hexadiene. In general, the homogeneous catalysts are much more effective than their heterogeneous counterparts in the incorporation of diene monomers in PE structure. Especially, the single-site Et(Ind)(2)ZrCl2/MAO catalyst with a strained geometry provides unsaturated PE with narrow molecular weight distribution and controllable diene concentration. It is not expected that the catalyst activity systematically increases with the concentration of 1,4-hexadiene. Employing a combination of unsaturated PE and borane reagents, many LLDPE-f polymers, containing borane, hydroxy, amino, and silane groups, were obtained despite heterogeneous reaction conditions. Apparently the double bonds in the side chain are located in the amorphous phase and are available for reaction with reagents.