Second coordination sphere effect of benzothiophene substituents on chain transfer and chain walking in ethylene insertion polymerization

• Published in: Polymer (Guilford) Vol. 245; p. 124707
• Main Authors: Wang, Hui, Duan, Gaokun, Fan, Huijun, Dai, Shengyu
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 06.04.2022; Elsevier BV
• Subjects: Benzothiophene; Catalysts; Chain transfer; Coordination; Diimide; Ethylene polymerization; High temperature; Low temperature; Mechanical properties; Molecular weight; Naphthyl and benzothiophene groups; Nickel; Polyethylene; Polyethylenes; Polymerization; Second coordination sphere effect; Thermal stability; α-diimine Ni(II) catalysts; Second coordination sphere effect; Ethylene polymerization; Naphthyl and benzothiophene groups; α-diimine Ni(II) catalysts
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/j.polymer.2022.124707

Recently, the α-diimine Ni(II) and Pd(II) catalysts bearing various diarylmethyl substituents on the N-aryl group have drawn much attention. In this work, two bulky diarylmethyl α-diimine Ni(II) catalysts bearing naphthyl and benzothiophene groups were synthesized and employed in ethylene polymerization. The Ni(II) complex bearing naphthyl groups exhibited high activities (ca. 106 g mol−1 h−1) and yielded highly branched (60–70/1000C) polyethylenes with high molecular weights (Mn up to 784.5 kg/mol) in ethylene polymerization. Moreover, this complex exhibited excellent thermal stability at high temperatures, and the polyethylene products obtained demonstrated good mechanical properties (SR up to 59%). Meanwhile, the Ni(II) complex bearing benzothiophene groups displayed high activities (ca. 106 g mol−1 h−1), and generated lightly branched (15–37/1000C) polyethylene with particularly high molecular weights (Mn up to 2017.6 kg/mol) at low temperatures. At high temperatures, the polymerization activity and the molecular weight of the obtained polyethylene decreased significantly. The second coordination sphere effect of benzothiophene substituents is considered to be responsible for the above experimental results. Synopsis: The Ni(II) complex bearing naphthyl groups yielded highly branched polyethylenes with good elastic recovery while Ni(II) complex containing benzothiophene groups generated lightly branched UHMWPE. [Display omitted] •Suppression of chain transfer and chain walking via second coordination sphere effect of benzothiophene substituents.•Polyethylene products obtained demonstrated good mechanical properties.•Lightly branched (15–37/1000C) polyethylene with particularly high molecular weights (Mn up to 2017.6 kg/mol).