Unsymmetrical Fluorinated α‑Diimine Nickel Catalysts with Synergistic Steric and Fluorine Effects: toward Ethylene-Based Elastomers and Polar Copolymers

Polyolefin
elastomers and polar-functionalized polyethylene
are
crucial high-performance materials, yet their synthesis is constrained
by trade-offs among molecular weight, polar comonomer incorporation,
and catalyst stability. To address these challenges, we developed
a series of unsymmetrical α-diimine Ni(II) catalysts (Ni1–Ni5) that integrate steric shielding
with a “fluorine effect.” Incorporation of a bulky dibenzhydryl
substituent enhances thermal stability, while an ortho-fluorinated N-aryl unit electronically modulates
the active site and suppresses chain transfer. These catalysts exhibit
high activity and robustness in ethylene polymerization, affording
polyethylene with high molecular weights (Mn up to 2.99 × 105 g·mol–1). Notably, the optimal catalyst further enables direct
copolymerization of ethylene with long-chain ω-unsaturated alcohols
and esters, yielding functionalized polyethylenes with appreciable
polar comonomer incorporation. Furthermore, the resulting materials
display excellent elastomeric properties, including excellent tensile
strength (up to 34.6 MPa) and significantly enhanced elastic recovery
(SR up to 68%), demonstrating the effectiveness of this catalyst design
strategy.