Branched polyethylene (PE) was prepared with a novel (alpha-diimine)nickel(II) complex of 2,3-bis(2,6-dimethylphenyl)-butanediimine nickel dichloride {[2,6-(CH3)(2)C6H3-N=C(CH3)C(CH3)=N-2,6-(CH3)(2)C6H3]NiCl2} activated by methylaluminoxane in the presence of a single ethylene monomer. The influences of various polymerization conditions, including the temperature, Al/Ni molar ratio, Ni catalyst concentration, and time, on the catalytic activity, molecular weight, degree of branching, and branch length of PE were investigated. According to gel permeation chromatography, the weight-average molecular weights of the polymers obtained ranged from 1.7 X 10(5) to 6.0 X 10(5), with narrow molecular weight distributions of 2.0-3.5. The degree of branching in the polymers rapidly increased with the polymerization temperature increasing; this led to highly crystalline to totally amorphous polymers, but it was independent of the Al/Ni molar ratio and catalyst concentration. At polymerization temperatures greater than 20degreesC, the resultant PE was confirmed by C-13-NMR to contain significant amounts of not only methyl but also ethyl, propyl, butyl, amyl, and long branches (longer than six carbons). The formation of the branches could be illustrated by the chain walking mechanism, which controlled their specific spacing and conformational arrangements with one another.