2-[2,6-Bis(4,4′-difluorobenzhydryl)-4-methylphenylimino]-3-aryliminobutylnickel complex precatalysts tuning polyethylene elastomers with different molecular weights

A series of 2-[2,6-bis(4,4'-difluorobenzhydryl)-4-methylphenylimino]-3-aryliminobutylnickel complexes was synthesized and fully characterized using FT-IR, elemental analysis, and single-crystal X-ray diffraction in the case of Ni1. The structural analysis revealed significant deviation from ideal tetrahedral geometry. When activated with MAO, these complexes demonstrated superior catalytic performance compared to previously reported unsymmetrical 2,3-bis(arylimino)butylnickel analogs. The optimized system, incorporating <i>ortho</i>-difluorobenzhydryl and <i>para</i>-methyl electron-donating groups, achieved an exceptional activity of 26.56 × 10⁶ g(PE) mol^-1 (Ni) h^-1. The resulting polyethylenes exhibited a broad spectrum of microstructures, ranging from semi-crystalline to nearly amorphous, with unimodal ultra-high molecular weights (<i>M</i> _w: 4.33-26.72 × 10⁵ g mol^-1) and tunable branching degrees (62-200/1000 C) achieved through a controlled chain-walking mechanism. The unique balance of molecular weight and crystalline-amorphous regions in these polymers translated to outstanding mechanical properties, including tensile strengths of 1.68-13.42 MPa, elongations at break of 388-529%, and elastic recoveries of 21-73%. Notably, the Ni1/Et₂AlCl catalyst system demonstrated enhanced thermal stability for ethylene polymerization, achieving a higher activity of 2.56 × 10⁶ g(PE) mol^-1 (Ni) h^-1 at 90 °C compared to 1.94 × 10⁶ g(PE) mol^-1 (Ni) h^-1 at 70 °C for Ni1/MAO. However, the polymers produced with Ni1/Et₂AlCl exhibited lower molecular weights (2.67-10.90 × 10⁵ g mol^-1) and inferior mechanical properties, underscoring the critical role of molecular weight in determining material properties.