Long—chain branched polyethylene was prepared by a bianary catalyst system[Cat 1：bis(α— naphthalidine)-butanediimine)NiBr2 and Cat 2：bis(2

6-diisopropylphenyl)-acenaphthenediimine NiBr2]．The binary catalyst system showed a good synerglc effect．Its polymerization activity(4．6×105g PE／mol Ni·h) was higher than that of either single catalyst．The resultant highly branched(94．8～144．5／1000C)PE was confirmed by 13C-NMR to contain a significant amount(27～42／1000C)of long chain branches(n≥6)．The GPC results showed that the molecular weight distribution of the polyethylene obtained with this binary catalyst system was very narrow．The explanation for this is that ethylene oligomerizes in the Cat 1 active site

and the produced vinyl end group oligomers serving as comonomers in shu copolymcrize with the growing polyethylene chain in the active site of Cat 2．