Three new three‐dimensional geometry bulky α‐diimine ligands (L) containing electron‐donating and electron‐withdrawing groups, 9,10‐dihydro‐9,10‐ethanoanthracene‐11,12‐di(Ar)imine (Ar = p‐PhCH3, L1; Ar=p‐PhCl, L2; Ar=p‐PhCF3, L3.), and their corresponding single Ni(II) catalysts,NiL2Br2 (Ni(L1)2Br2, Ni(L2)2Br2, and Ni(L3)2Br2, were synthesized and the molecular structure were determined by X‐ray crystallography. All NiL2Br2 catalysts were tested for norbornene polymerization and copolymerization of norbornene with 1‐alkene after activation with B(C6F5)3. The results that the polymerization catalytic activities for norbornene up to 105 gpolymer/molNi·h even at 140 °C, shown that NiL2Br2 catalysts have high thermal stability. Meanwhile, catalysts with electron‐withdrawing groups could achieve higher reactivity. The obtained poly(NB‐co‐1‐alkene)s were confirmed to be vinyl‐addition copolymers and noncrystalline. All copolymers exhibited high 1‐alkenes insertion ratio, good thermal stability (Td > 375 °C), high molecular weight (up to 105 g/mol), good solubility in common organic solvents and could be processed into films with good transparency in the visible region. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3495–3505