Five types of unsymmetrical bis(arylimino)acenaphthenes, 1-[2,4,6-(CHPh₂)₃C₆H₂N]-2-(ArN)C₂C₁₀H₆ (Ar = 2,6-Me₂Ph L1, 2,6-Et₂Ph L2, 2,6-i-Pr₂Ph L3, 2,4,6-Me₃Ph L4 and 2,6-Et₂-4-MePh L5), each containing a single N-2,4,6-tribenzhydrylphenyl group, have been prepared and fully characterized. The interaction of L1–L5 with (DME)NiBr₂ (DME = 1,2-dimethoxyethane) afforded the corresponding 1:1 nickel(II) bromide chelates, LNiBr₂ (Ni1–Ni5), in good yield. Distorted tetrahedral geometries are a feature of the X-ray structures of Ni1 and Ni3; broad paramagnetically shifted peaks are seen in the ¹H NMR spectra for all the nickel complexes in solution. Upon activation with relatively low amounts of Et₂AlCl or Me₂AlCl (200–700 equivalents), Ni1–Ni5 exhibited exceptionally high activities for ethylene polymerization (up to 1.07 × 10⁷ g of PE (mol of Ni)⁻¹ h⁻¹), displayed good thermal stability [2.97 × 10⁶ g of PE (mol of Ni)⁻¹ h⁻¹ even at 90 °C] and produced hyperbranched polyethylenes. Dynamic mechanical analysis and stress–strain testing reveal that the polymeric materials possess good elastomeric recovery and high elongation at break, indicating a promising alternative material to thermoplastic elastomers (TPEs).