Multifluoro Enhanced 1,2‑bis(imino)acenaphthylnickel Precatalysts for Ethylene Polymerization: Control of Chain Walking and Polyethylene Properties

Abstract

A series of multifluoro enhanced 1,2bis(imino)acenaphthene derivatives has been synthesized and used in forming their nickel complexes via a facile two step strategy. Upon activation with EASC (ethylaluminum sesquichloride), all complexes exhibited exceptionally high activities and produced high to ultra-high molecular weight polyethylenes, displaying the remarkable thermal endurance from 30°C to 80°C with minimal activity loss. Chain walking was heavily affected by the ligands substituents and polymerization temperature, which resulted in semicrystalline to highly branched polyethylene. The lower branched sample correlated with higher melting temperatures as well as higher densities, which directly corresponded to the tunable mechanical and elastic properties. Notably, the polyethylene obtained at high polymerization temperature (80°C) maintained an exceptional tensile strength (23.4 MPa) with a high elongation at break (935%) as well as outstanding toughness (8990 MJ m⁻³) and good elastic recovery (74%). Furthermore, polyethylene prepared in n-hexane, an industrially relevant solvent, exhibited higher branches and superior elastic recovery in comparison to those produced in toluene. Moreover, easily prepared nickel complexes were well identified by spectroscopic measurements along with the single crystal X-ray diffraction revealing distorted tetrahedral, octahedral, and square pyramidal geometries.