Vinyl-addition polymerization of norbornene was accomplished by two novel dinuclear diimine nickel dichloride complexes in combination with methylaluminoxane (MAO). The activities were moderate. The catalyst structure, Al/Ni molar ratio, solvents, and polymerization temperature all affected the catalytic activities. The obtained polynorbornenes were characterized by H-1-NMR, C-13-NMR, FTIR, DSC, WAXD, and intrinsic viscosity measurements. The vinyl-addition polymers were amorphous but with a short-range order and high packing density. The polynorbornenes showed glass transition temperatures (T-g) above 240degreesC and decomposed above 400degreesC. The catalyst structure and polymerization conditions have effects on the molecular weight and the microstructure of the polymers. The nickel complex with bulkier substituents in the ligand produced polynorbornene with a higher packing density and higher regularity and, therefore, with higher T-g. (C) 2003 Wiley Periodicals, Inc.