The attempt to copolymerize ethylene and styrene using eta(3)-methllyl-nickel-diimine {[eta(3)-2-MeC3P4]Ni[1,4-bis(2,6-diisopropylphenyl)C2H2N2][PF6]} (1) associated with MAO or TMA produces polystyrene. : polyethylene and polyethylene with styrene end groups. : Characteristics of the formed polymer depend on the reaction conditions. The presence of styrene in the medium reduces the polymerization productivity and the molecular weight of polyethylene. Incorporation of styrene into polyethylene is favored by a 1/ethylene/MAO pre-contact time and depends on the amount of styrene. Maximum incorporation was 4.4 wt.-%. If styrene is introduced after the pre-contact time, a bimodol product distribution is observed, suggesting the occurrence of two different catalytic species. If the co-catalyst is changed from MAO to TMA, no copolymer is formed but the presence of styrene leads to higher amounts of branched polyethylene.