Iterative Exponential Growth of Oxygen-Linked Aromatic Polymers Driven by Nucleophilic Aromatic Substitution Reactions

• Main Authors: Tyler J. Jaynes, Mona Sharafi, Joseph P. Campbell, Jessica Bocanegra, Kyle T. McKay, Kassondra Little, Reilly Osadchey Brown, Danielle L. Gray, Toby J. Woods, Jianing Li, Severin T. Schneebeli
• Format: Article
• Language: English
• Published: Frontiers Media S.A. 2021-04-01
• Series: Frontiers in Chemistry
• Subjects: iterative convergent/divergent polymer synthesis; SNAr reactions; nonclassical hydrogen bonding; nuclear magnetic resonance spectroscopy; polymer folding; iterative exponential polymer growth
• Online Access: https://www.frontiersin.org/articles/10.3389/fchem.2021.620017/full

This work presents the first transition metal-free synthesis of oxygen-linked aromatic polymers by integrating iterative exponential polymer growth (IEG) with nucleophilic aromatic substitution (SNAr) reactions. Our approach applies methyl sulfones as the leaving groups, which eliminate the need for a transition metal catalyst, while also providing flexibility in functionality and configuration of the building blocks used. As indicated by 1) 1H-1H NOESY NMR spectroscopy, 2) single-crystal X-ray crystallography, and 3) density functional theory (DFT) calculations, the unimolecular polymers obtained are folded by nonclassical hydrogen bonds formed between the oxygens of the electron-rich aromatic rings and the positively polarized C–H bonds of the electron-poor pyrimidine functions. Our results not only introduce a transition metal-free synthetic methodology to access precision polymers but also demonstrate how interactions between relatively small, neutral aromatic units in the polymers can be utilized as new supramolecular interaction pairs to control the folding of precision macromolecules.