A tandem catalytic system, composed of (η5-C5H4CMe2C6H5)TiCl3 (1)/MMAO (modified methyl aluminoxane) and [(η5-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.