Nickel-catalyzed direct synthesis of hyperbranched liquid oligoethylene†

Abstract

Late transition metal-catalyzed ethylene chain-walking polymerization offers a remarkably convenient method for synthesizing hyperbranched polyethylene. In this study, we created a series of pyridine-imine Ni(ii) complexes with axially flexible cycloalkyl substituents, tailored for the production of hyperbranched oligoethylene oils (HBOEOs). These complexes exhibited moderate activity in HBOEO synthesis, reaching rates of up to 4.90 × 10⁵ g mol⁻¹ h⁻¹. The resulting products exhibited low molecular weights (325–523 g mol⁻¹) and high branching densities (110–167/1000C). NMR analysis verified their diverse branching structures, with a significant proportion of hyperbranched motifs. Notably, the activity, structure, and properties of the HBOEOs produced by the catalytic system were significantly influenced by alterations in the catalyst structure and oligomerization conditions. Specifically, when compared to rigid phenyl substituents, flexible cycloalkyl substituents proved more effective in promoting the catalytic system to produce HBOEOs with a higher degree of branching and improved liquefaction properties.