[3-Cyano-2-(2,6-diisopropylphenyl)aminopent-2-en-4-(phenylimine) tris (pentafluorophenyl)borate](eta(5)-C5H5)ZrCl2, [(B(C6F5)(3)-NC-nacnac)CpZrCl2], precatalyst (2) can be treated with low concentrations of methylaluminoxane (MAO) to generate active sites capable of copolymerizing ethylene with 1-octadecene or norbornene under mild conditions. A series of poly(ethylene-co- octadecene) and poly(ethylene-co-norbornene) copolymers were prepared, and their properties were characterized by NMR, differential scanning calorimetry, and mechanical analysis. The results show that this system produced poly(ethylene-co- octadecene) copolymers with a branching content of about 8 mol %. However, upon increasing the comonomer concentration, a drastic reduction in the M-n of the product is observed concomitant with an increase in comonomer incorporation. This leads to a gradual decrease in Young's modulus and stress at break, indicating an increase in the "softness'' of the copolymer. In the case of copolymerizations of ethylene and norbornene, the catalytic system (2/MAO) shows a substantial decrease in reactivity in the presence of norbornene and generates copolymer chains in which 5-10 mol % norbornene is in blocks. We also observe that ethylene norbornene copolymers exhibit a high degree of alternating insertions (close to 50%), as determined by NMR spectroscopy. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1535-1542, 2011