Novel Nickel-diimine pre-catalyst (1NiBr 2) containing N,N-bis(diphenylmethylene)-ethylenediamine ligand was able to quantitatively polymerize norbornene (NBE) into polynorbornene (PNBE) at 50 °C upon activation with methylaluminoxane (MAO). The monomer concentration governs the rate of reaction and the polymer characteristics. Thermal and spectral analysis revealed the polymerization pathway to occur via vinyl addition and not ring opening. The homopolymerization of 1-hexene or ethylene could not be achieved using 1NiBr 2/MAO catalyst system, but the presence of 1-hexene did not prevent the quantitative polymerization of NBE without 1-hexene incorporation. The characteristics of the polymers formed were found to be different in terms of solubility and molecular weight compared to those of the product generated by the homopolymerization of NBE in the absence of 1-hexene. Here 1-hexene acted as a chain transferring agent and control the molecular weight of PNBEs produced. © 2011 Springer-Verlag.