Synthesis of High-Molecular-Weight Branched Polyethylene Using a Hybrid "Sandwich" Pyridine-Imine Ni(II) Catalyst

You Ge; Qi Cai; Yuyin Wang; Jiangang Gao; Yue Chi; Shengyu Dai

doi:10.3389/fchem.2022.886888

Synthesis of High-Molecular-Weight Branched Polyethylene Using a Hybrid "Sandwich" Pyridine-Imine Ni(II) Catalyst

Front Chem. 2022 May 4:10:886888. doi: 10.3389/fchem.2022.886888. eCollection 2022.

Authors

You Ge^{1

2}, Qi Cai¹, Yuyin Wang³, Jiangang Gao¹, Yue Chi³, Shengyu Dai^{1

2}

Affiliations

¹ School of Chemical and Environmental Engineering, Anhui Polytechnic University, Wuhu, China.
² Institutes of Physical Science and Information Technology, Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of Education, Anhui University, Hefei, China.
³ Key Laboratory of Advanced Structural Materials of Ministry of Education, College of Material Science and Engineering, College of Chemistry and Life Science, Advanced Institute of Materials Science, Changchun University of Technology, Changchun, China.

Abstract

Most pyridine-imine Ni(II) and Pd(II) catalysts tend to yield low-molecular-weight polyethylene and ethylene-based copolymers in olefin insertion polymerization, as the unilateral axial steric structure of such complexes often cannot provide effective shielding of the metal center. In this study, we synthesized a series of hybrid "semi-sandwich" and "sandwich" type pyridine-imine Ni(II) complexes by incorporating diarylmethyl or dibenzosuberyl groups onto 8-aryl-naphthyl motif. The as-prepared Ni(II) complexes afforded highly branched polyethylene with high molecular weights (level of 10⁵ g/mol), and moderate activities (level of 10⁵ g/(molh)) in ethylene polymerization. Most interestingly, compared to "semi-sandwich" Ni(II) complexes bearing (2-diarylmethyl-8-aryl)naphthyl units, the "full-sandwich" counterpart containing (2-dibenzosuberyl-8-aryl)naphthyl motif was able to produce higher-molecular-weight polyethylene with higher branching density. In addition, the effect of remote non-conjugated electronic substituents in diarylmethyl groups of the Ni(II) system was also observed in ethylene polymerization.

Keywords: Ni(II) and Pd(II) catalysts; high-molecular-weight; highly branched; hybrid “sandwich”; pyridine-imine.