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

Abstract

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.