Immobilization of α-diimine nickel (II) catalysts on multi-walled carbon nanotube for slurry ethylene polymerization

Abstract

Homogeneous α-diimine nickel (II) catalyst complexes, with and without amino para-aryl position functionality, were synthesized. These complexes were immobilized on carboxyl, hydroxyl, and acyl chloride functionalized multi-walled carbon nanotubes to form five novel heterogeneous α-diiminonickel catalysts. Immobilization was performed by covalent or electrostatic bonding via methylaluminoxane (MAO) linker or amide linkage. All the immobilized catalysts were fully characterized and their structures and supporting efficiencies were determined. Both the nature of α-diimine ligands and the kind of interaction between anchored catalyst complexes and multi-walled carbon nanotube surface influenced the catalytic performance, microstructure, and morphology of obtained polyethylenes. Catalysts immobilized by covalent bonds showed higher activities than physisorbed ones with the trend of activity rising versus temperature. Reaction between ligand amino para-aryl position and multi-walled carbon nanotube acyl chloride functionality resulted in immobilization through amide linkage. This procedure prepared catalyst with the lowest relative weight loss in thermogravimetry analysis and highest activities up to 5863 g PE mmol−1Ni h−1. The catalyst produced polyethylene with dense botryoidal morphology, highest molecular weight distributions and highest melting points up to 14.1 at 60 °C and 133 °C at 30 °C in polymerization trials, respectively.