High-Performance -Diimine Nickel Complexes for Facile Access of PE Elastomers with Exceptional Material Properties

For practicable elastomeric polyethylene, achieving high catalyst thermal stability and activity, along with precise control of polymer properties such as branching density, molecular weights, and distribution, is crucial but challenging. In this study, two sets of symmetrical alpha-diimine nickel complexes, each comprising four nickel bromide or chloride complexes, were synthesized and investigated their performance for ethylene polymerization under various reaction conditions. Upon activation with either Et2AlCl or MMAO cocatalysts, these complexes displayed not only high activity but also generated high molecular weight polyethylenes with controlled polydispersity and a substantial number of branches. The catalyst with the least steric hindrance displayed the remarkable high activity (up to 1.2x10(7) gmol(-1)h(-1)). Notably, nickel bromides demonstrated higher activity compared to their chloride counterparts. The investigation into the effect of reaction temperature on catalytic performance revealed that NiBrMe-MMAO system displayed high thermal stability (activity up to 2.51x10(6) gmol(-1)h(-1) at 100 degrees C) and consistently yielded high polymer molecular weights with narrow polydispersity over a broad temperature range of 30-100 degrees C. Of significant note, mechanical analysis of the resulting polyethylene demonstrated excellent ultimate tensile strength and high strain at break. Particularly, the polyethylene sample prepared at 100 degrees C exhibited ultimate tensile strength up to 10 MPa with 1863% maximum strain at break and a strain recovery of up to 54.9% after ten cycles at a fixed strain of 300%, indicating excellent material properties of prepared thermoplastic polyethylene elastomers (TPE).