Synthesis of Branched Polyethylene and Ethylene-MA Copolymers Using Unsymmetrical Iminopyridyl Nickel and Palladium Complexes

Abstract

It is usually challenging to obtain high-molecular-weight polyethylene in the iminopyridyl Ni(II) and Pd(II) system due to the only one side axial steric structure of the iminopyridine ligand. In this study, the effectiveness of the dibenzosuberyl substituent in retarding the chain transfer in the iminopyridyl Ni(II) and Pd(II) catalysts has been demonstrated. The complexes Ni5 and Pd5 with phenyl and dibenzosuberyl substituents are noted to generate polyethylene and ethylene-MA copolymers with significantly higher molecular weight as compared to the complexes Ni1−4 and Pd1−4 with various diarylmethyl moieties. The synergistic effect of phenyl and dibenzosuberyl groups can further enhance the function of the catalyst to suppress the chain transfer. Further, polyethylene, ethylene oligomers, and ethylene-MA co-oligomers obtained in this study are observed to be highly branched. In addition, the iminopyridyl palladium catalysts can effectively promote the copolymerization of ethylene and MA to obtain the polar functionalized ethylene-MA co-oligomers with high incorporation ratios (up to 15.2 mol %).

Direct synthesis of hyperbranched ethene oligomers and ethene‐MA co‐oligomers using iminopyridyl systems with weak neighboring group interactions

“…The iminopyridyl system has been known for the synthesis of low-molecular weight polyethylene since it was reported 20 years ago. 13 Many researchers [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] have been successful in improving the system through the Huijun Fan and Guoyong Xu are equal first authors. introduction of bulky ortho-aryl substituents, modification of the pyridine backbone and regulation of electronic effects (Chart 1A-D).…”

“…The activity, molecular weight and microstructure of the products yielded in the system can be highly modulated. [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] Recently, we developed a series of N-terphenyl iminopyridyl Ni(II) and Pd(II) complexes and they were highly effective in the preparation of hyperbranched ethene oligomers and ethene-MA co-oligomers (Chart 1D). [32][33] A π-interaction of a phenyl group with the metal center is responsible for the results of the above experiments.…”

“…The iminopyridyl system has been known for the synthesis of low‐molecular weight polyethylene since it was reported 20 years ago 13 . Many researchers 13–31 have been successful in improving the system through the introduction of bulky ortho‐aryl substituents, modification of the pyridine backbone and regulation of electronic effects (Chart 1A–D). The activity, molecular weight and microstructure of the products yielded in the system can be highly modulated 13–31 .…”

“…Many researchers 13–31 have been successful in improving the system through the introduction of bulky ortho‐aryl substituents, modification of the pyridine backbone and regulation of electronic effects (Chart 1A–D). The activity, molecular weight and microstructure of the products yielded in the system can be highly modulated 13–31 . Recently, we developed a series of N‐terphenyl iminopyridyl Ni(II) and Pd(II) complexes and they were highly effective in the preparation of hyperbranched ethene oligomers and ethene‐MA co‐oligomers (Chart 1D).…”

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

“…( Fan et al, 2021 ; Yan et al, 2022 ; Fan et al, 2022 ) In addition, the effectiveness of a single dibenzosuberyl group in unsymmetrical iminopyridyl Ni(II) and Pd(II) catalysts in retarding the chain transfer was also demonstrated ( Chart 1E ). ( Ge et al, 2021 ) In this study, the dibenzosuberyl and 8-aryl-naphthyl units are integrated into the pyridine-imine nickel catalyst at the same time and the resulting hybrid “sandwich” catalyst is capable of catalyzing ethylene polymerization to yield highly branched polyethylene with high molecular weights ( Chart 1F ).…”