Fluoro-enriched α-diimine nickel precatalysts for enhanced thermostability in synthesis of polyethylene elastomer

The microstructural, thermal, and physical properties of α-diimine nickel-catalyzed polyethylene are customizable due to the unique chain-walking characteristic of these catalysts. Through a stepwise reaction strategy, a set of five new 1,2-bis(imino)acenaphthenequinone-nickel complexes, each adorned with seven fluoro groups were prepared and then evaluated for ethylene polymerization. Employing two alkylaluminium cocatalysts individually (EASC or MMAO), these nickel precatalysts displayed high polymerization activities (up to 2.9 × 10⁷ g mol⁻¹ h⁻¹ at 30 °C), producing branched polyethylene with high molecular weights (M_w ≈ 10⁵ g mol⁻¹) and excellent mechanical properties. Compared to previous analogues, the incorporation of a higher number of fluoro groups gave higher thermal stability with an exceptionally high activity of 2.7 × 10⁶ g mol⁻¹ at 100 °C. The branching density varied from 63 to 94/1000C at 30 °C, depending on the ligand structure, while increase of temperature raised the branching degree to 109/1000C at 100 °C. These variations in branching significantly influenced the polymer melt temperature, mechanical, and elastic properties, resulting in polyethylene with high tensile strength (σ_b = up to 11 MPa), low Young modulus (E = up to 5.5 MPa), and good elastic properties (SR = up to 61 %).