Synthesis of chain‐end functionalized highly branched polyethylene waxes using sterically open α‐diimine Ni(II) catalysts

Abstract

Our previous research showed that bis(benzocyclopentyl) α‐diimine Pd(II) complexes can facilitate chain transfer and polar monomer insertion in ethylene (co)polymerization. In this study, we synthesized two bis(benzocyclopentyl) α‐diimine Ni(II) complexes with different backbones. The Ni(II) complexes exhibited high activities (0.63–7.23 × 106 g·mol−1 h−1) and produced low molecular weight (2.7–7.8 kg mol−1) polyethylene waxes with high branching densities (43–86/1000 C) in ethylene polymerization. The use of a catalyst with a butyl backbone resulted in polyethylene waxes with significantly higher molecular weights. The axial substituent restriction strategy employed in the nickel catalyst allows for a sterically open structure, reducing the molecular weight of the resulting polyethylene by over two orders of magnitude, compared to ethyl catalysts without axial restrictions. This enables the production of polyethylene wax grade products with improved properties. The branched polyethylene wax chain ends were found to be aryl‐functionalized according to NMR characterization analysis, while the double bonds were absent. Also, the choice of solvent affects the branching, molecular weight, and chain end composition of the polyethylene wax.