Suppression of Chain Walking and Chain Transfer in Ethylene (Co)Polymerization with Iminodibenzyl Substituents Containing Second Coordination Spheres

Abstract

Chain walking and chain transfer are the two most important events that determine the structure and molecular weight of the resulting polyolefin in the most imine-based late transition metal-catalyzed ethylene (co)polymerization. In this study, we have demonstrated that the nitrogen-containing iminodibenzyl substituents are effective in suppression of chain walking and chain transfer during the α-diimine Ni(II)-and Pd(II)-catalyzed ethylene (co)polymerization. For this purpose, several α-diimine Ni(II) and Pd(II) complexes with N-diphenyl or iminodibenzyl substituents have been designed, prepared, and described. In the case of nickel-catalyzed ethylene polymerization, the iminodibenzyl Ni(II) catalyst exhibited higher activities and yielded polyethylenes with orders of magnitude higher molecular weights than the N-diphenyl Ni(II) catalyst. Similar observations were also found in the polymerization of ethylene and copolymerization of ethylene with methyl acrylate catalyzed by the corresponding palladium catalysts. Compared to the corresponding dibenzosuberyl Ni(II) and Pd(II) catalysts, the iminodibenzyl catalysts exhibited an excellent ability to suppress the chain walking process and produced (co)polymers with significantly lower branching densities during ethylene (co)polymerization. It was proposed that the observed phenomenon is caused by second coordination sphere effects of the iminodibenzyl substituents.

Noncovalent Interactions in Late Transition Metal-Catalyzed Polymerization of Olefins

“…Chen and Dai also found that α-diimine nickel catalysts 11 and 12 (Figure ) produced more linear and higher molecular weight polyethylenes because the H···X hydrogen bonding interactions (X = F, N) significantly suppressed the chain walking and chain transfer processes during ethylene polymerization. , Besides, the H···F hydrogen bonding interactions also effectively promote the ethylene polymerization catalyzed by the α-diimine nickel catalyst 13 (Figure ) to produce higher molecular weight polyethylene. The effects of H···F hydrogen bonding interaction are clearly verified by computational approaches …”