ortho/para-Chlorinated α‑Diimine Nickel Precatalysts Resulting Polyethylenes with Improved Mechanical Properties and Controlled Crystallinity

A series of ortho/para-chlorinated N-(6-benzhydryl-2,4-dichlorophenylimino)-N’-aryliminoacenaphthylene derivatives as ligands (L1-L6, aryl = 2,6-dimethylphenyl (L1), 2,6-diethylphenyl (L2), 2,6-diisopropylphenyl (L3), 2,4,6-trimethylphenyl (L4), 2,6-diethyl-4-methylphenyl (L5), 6-benzhydryl-2,4-dichlorophenyl (L6)) were successfully synthesized and used for their corresponding nickel complexes (Ni1-Ni6). All organic compounds were comprehensively characterized using NMR, FT-IR, and EA techniques; the nickel complexes had their components determined through FT-IR and EA analysis, and the unambiguous molecular structures of representative nickel complexes were confirmed via single-crystal X-ray diffraction, revealing that Ni1 and Ni3 possessed a distorted octahedral geometry around the nickel center. Upon activation with EASC, all nickel complexes demonstrated high catalytic activity (4.7 to 37.9 × 106 g mol–1 h–1) for ethylene polymerization, with Ni1 achieving peak performance (12.2 × 106 g mol–1 h–1) at 50 °C in 30 min. Impressively, the catalytic system demonstrated exceptional thermal stability, maintaining high activity above 9 × 106 g mol–1 h–1 across a broad temperature range (40–70 °C) with minimal fluctuations. Contrary to typical chain-walking behavior observed in α-diimine nickel catalysts, the resultant polyethylene exhibited high crystallinity and minimal long-chain branching despite narrow polydispersity (Đ = 1.8–2.9) and moderate molecular weights (tens of thousands). Systematic modulation of ligand structure and polymerization conditions enabled precise control over crystallinity (Xc: 6.4 to 62.6%), which was directly correlated with tunable mechanical properties (σb: 1.9–13.1 MPa, εb: 178.8–1030.6%). Representative samples of the resultant polyethylene displayed exceptional tensile strength (13.1 MPa), high elongation at break (1030.6%), and notable elastic recovery (65%), suggesting new types of thermoplastic elastomers.