Targeting Highly Linear Polyethylenes with Different Molecular Weights Through Finely Tuning Substituents

Abstract

Targeting phase-change materials with cheap and clean advantages, the linear polyethylenes are highly demanded along with the correlations between the dispersity and melting range or the molecular weight and melting point. A series of 4,4'-dichlorobenzhydryl-substituted 2,6-diaryliminopyridyliron dichlorides (Fe1 – Fe5) is prepared and used as efficient catalysts in polymerizing ethylene to form polyethylenes with highly linear property but having different molecular weights and dispersity. Activated with MAO, all iron precatalysts perform high activities up to 2.0 × 10⁷ g of PE (mol of Fe)⁻¹ h⁻¹ resulting bimodal polyethylenes; meanwhile, activated with MMAO, the analog systems efficiently polymerize ethylene for polymers with lower molecular weights, being as polyethylene waxes. Combining the features of substituents with different electronic and steric effects, therefore, their catalytic performances have been finely controlled in tailoring microstructures of resultant polyethylenes. In addition, all iron complexes are fully characterized by FT-IR spectroscopy, high resolution mass spectroscopy and elemental analysis; moreover, the representative complexes Fe3 and Fe4 are confirmed by the single crystal X-ray diffraction.