The polymerizations of norbornene were investigated using a series of bis(O-ketoamino)nickel(II) complexes(1-6) in combination with methylaluminoxane (MAO) in toluene solution. The effects of catalyst structure, Al/Ni molar ratio, reaction temperature, and reaction time on catalytic activity and molecular weight of the polynorbornene were examined in detail. The electronic effect of the substituent around the imino group in the ligand is stronger than the steric bulk one on the polymerization activities, and the activities are in the order of 1 > 2 > 4 > 5 > 6 > 3. The obtained polynorbornenes were characterized by means of H-1-NMR, C-13-NMR, FTIR, TG, and WAXD techniques. The analyses results of polymers' structures and properties indicate that the polymerization reaction of norbornene runs in vinyl-addition polymerization mode. The obtained polynorbornene was confirmed to be vinyl-type and atactic polymers and showed good thermostability (T-dec > 458 degrees C) and were noncrystalline but had short-range order. (c) 2006 Wiley Periodicals, Inc.