Synthesis of high MFI polyolefin elastomers using dibenzosuberyl iminopyridyl Ni(ii) catalysts†

Abstract

Recently, nickel-based α-diimine catalysts have been widely used in the preparation of polyolefin elastomer materials. However, the polyolefin materials obtained from this system often exhibit high molecular weights, leading to a low melt flow index (MFI) and difficulties in film processing. Herein, we first report the synthesis and characterization of a class of nickel dibenzosuberyl iminopyridyl catalysts, featuring backbones and arylamine substituents with varying electronic effects. These catalysts demonstrate high activity (10⁶ g mol⁻¹ h⁻¹) in ethylene polymerization and enable the synthesis of polyethylene elastomers with moderate molecular weights (53.8–156.9 kg mol⁻¹) and branching densities (55–87/1000 C). The electronic properties of the catalyst backbone and the arylamine substituents have a general influence on ethylene polymerization and the properties of the resulting products. However, increasing the polymerization temperature significantly reduced the polymerization activity and altered the molecular weight and branching density of the obtained polyethylene elastomers. Mechanical property tests of these polyethylene elastomers reveal excellent elongation at break (1617%–1729%) and moderate tensile strength at break (5.46–10.58 MPa) and elastic recovery ratios (30%–45%). MFI tests, as well as transmittance and volume resistivity measurements, indicate that the obtained polyethylene elastomer materials possess high MFR (16–22 g per 10 min), high transmittance (84–89%), and high volume resistivity (151–321 × 10¹⁵ Ω m), making them suitable for use as photovoltaic encapsulant films.