Fluorine and hydroxyl containing unsymmetrical a-diimine Ni (II) dichlorides with improved catalytic performance for ethylene polymerization. (15th March 2023)

• Record Type: Journal Article
• Authors: Wu, Ruikai; Stieglitz, Lucas; Lehner, Sandro; Jovic, Milijana; Rentsch, Daniel; Neels, Antonia; Gaan, Sabyasachi; Rieger, Bernhard; Heuberger, Manfred
• Is Part Of: European polymer journal. Volume 186(2023)
• Publication Date: 2023-03-15
• Subjects: a-Diimine Ni (II) complexes -- Ethylene polymerization -- Catalytic behavior -- Polyethylene, polymer branches -- High molecular weight; Polymers -- Periodicals; Polymerization -- Periodicals; Polymères -- Périodiques; Polymérisation -- Périodiques; Polymerization; Polymers; Periodicals; Electronic journals; 547.705
• DOI: 10.1016/j.eurpolymj.2023.111830
• Languages: English
• ISSNs: 0014-3057

Abstract

Graphical abstract: Highlights: New series of novel a -diimine Ni (II) complexes with electronic and steric features. High catalytic activity and remarkable thermal stability in ethylene polymerization. Tailored chain-walking process and tunable PE microstructures. Abstract: A series of new tailored a -diimine Ni (II) complexes (Ni-OH, Ni-FOH, Ni-PhOH, and Ni-PhFOH ) containing bulky ortho - N -aryl groups with various dibenzhydryl substitutes was successfully synthesized, characterized and applied in ethylene polymerization. The a -diimine ligands and Ni (II) complexes were characterized by 1 H, 19 F, and 13 C NMR, elemental analysis, and high resolution electrospray ionization mass spectrometry (ESI-HRMS). The X-ray crystallographic study of metal complexes Ni-OH, Ni-FOH, and Ni-PhFOH revealed their distorted tetrahedral geometry. An unsymmetrical steric-enhancement design approach was employed to modulate the competition between the monomer insertion and the chain-walking process in ethylene polymerization. This facile design resulted in a high catalytic activity and yielded high molecular weight PE. The catalytic activity of these complexes was optimized by varying the polymerization conditions (temperature, time, and ethylene pressure), use of co-catalysts and variation of the Al/Ni ratio. When activated with modified methylaluminoxane (MMAO), these Ni complexes exhibited the activity as high as 29.1 × 10 6 g of PE (mol of Ni) −1 h −1 ), with a molecular weight of 1.81 × 10 6 g mol −1 . Their thermal stability was well pronounced at elevated temperatures; high activity of 2.88 × 10 6 g of PE (mol of Ni) −1 h −1 and high molecular weight PE (0.86 × 10 6 g mol −1 obtained at 90 °C). PEs with tunable branches and high melting points (127.5 °C) were obtained, which is a typical feature of LLDPE. The incorporation of fluorine atoms on N -aryl groups had a strong positive influence on the catalytic activity of the Ni complexes and favored the chain-growth process in the ethylene polymerization. Surprisingly, the simultaneous presence of terminal hydroxyl group in these complexes did not adversely affect their catalytic activity, while offering the possibility for covalent attachment to the solid supports for future heterogeneous polymerization.