High-Molecular-Weight Poly(aromatic amide) Foldamers via Living Polymerization

Polyaromatic amides (aramids) have been an important class of industrial polymers and have recently been extensively studied for biomimetic foldamer design. The inherent rigid structure and strong hydrogen (H)-bonding make linear aramids notoriously insoluble in non-H-bond-breaking solvents, and they are typically synthesized via polycondensation in H-bond-breaking solvents. Here, we report a chlorophosphonium iodide reagent that can activate aromatic carboxylic acids in the presence of aromatic primary and secondary amines. The synthesized reagent is inert toward H-bond-breaking solvents like dimethylacetamide and N-methyl-2-pyrrolidone, and allows living polymerization of aromatic amino acid monomers and oligomers in H-bond-breaking solvents for the first time. A foldamer-forming monomer was also polymerized in a living chain-growth fashion. Atomic force microscopy, scanning electron microscopy, small-angle X-ray scattering, and circular dichroism spectroscopy analyses strongly support the tubular helical nature of the synthesized foldamer.