Thermostability promotion of α-diimine nickel precatalysts tailored with 2,6-bis(bis(4-fluorophenyl)methyl)-3,4,5-trimethoxyaniline for PE elastomer synthesis

Abstract

The influence of axial steric hindrance in α-diimine nickel catalysts on ethylene polymerization is paramount for enhancing the catalytic performance especially in terms of thermal stability and polymer molecular weights. In this study, a set of five nonsymmetrical 1,2-bis(arylimino)acenaphthene–nickel complexes, incorporating 2,6-bis(bis(4-fluorophenyl)methyl)-3,4,5-trimethoxyaniline and 2,4,6-trialkylaniline moieties, was prepared to tailor the catalytic attributes for ethylene polymerization. In-depth studies on the polymerization of ethylene, using two different cocatalysts and different reaction conditions, revealed exceptional catalytic activities for these precatalysts with activity levels as high as 20.3 × 10⁶ g mol⁻¹ h⁻¹ at 30 °C and high molecular weights of the obtained polyethylene with adjustable branching degrees and distributions. Reactions at elevated temperatures validated the enhanced thermal stability of Ni-Me₂ precatalysts, displaying a noteworthy activity of 1.4 × 10⁶ g mol⁻¹ h⁻¹ at 100 °C. Polyethylene derived from more sterically hindered nickel complexes exhibited relatively higher molecular weights and branching degrees compared to less hindered analogues. This trend was consistent across mechanical and elastic properties, which ranged from 6.1 MPa to 10.6 MPa and 26% to 49%, respectively. Moreover, the manipulation of branching degree by increasing the reaction temperature led to an elastic recovery of up to 63%, indicating potential formation of thermoplastic polyethylene elastomers.