A tandem catalytic system, composed of (eta5-C5H4CMe2C6H5)TiCl3 (1)/MMAO (modified methyl aluminoxane) and [(eta(5)-C5Me4)SiMe2(tBuN)]TiCl2. (2)/MMAO, was applied for the synthesis of ethylene-hex-1-ene copolymers with ethylene as the only monomer stock. During the reaction; 1/MMAO trimerized ethylene to hex-1-ene, while 2/MMAO copolymerized ethylene with the in situ produced hex-1-ene to poly(ethylene-hex-1-ene). By changing the catalyst ratio and reaction conditions, a series of copolymer grades with different hex-1-ene fractions at high purity were effectively produced.