Structural Effects\non Solubility and Crystallinity\nin Polyamide Ionomers

Although polyamides have been an industrial staple for\ndecades,\ntheir solubility and processability remain limited due to the strong\nhydrogen bonding between amide groups. Here, we report a family of\npolyamides in which aryl rings, alkyl spacers, sulfonate groups, and\namide linkages are regularly spaced along the polymer backbone, allowing\nus to probe the structural elements that affect processability. We\naccessed these polymers through a synthetic route based on an expanded\ndiamine monomer and characterized them through a range of physical\nand spectroscopic techniques. Our results show that the combination\nof sulfonate groups with increased amide content results in highly\nsoluble polymers, which can dissolve in polar solvents such as water,\nmethanol, and <i>N</i>,<i>N</i>-dimethylformamide.\nInfrared spectroscopy on the solid polymers shows that the aliphatic\namides engage in hydrogen bonding with the sulfonate groups, thus\ninhibiting ion aggregation, crystallization, and microphase separation.\nThese findings expand the avenue to sulfonate-containing polyamide\nchemistry and provide design rules for the synthesis of more processable\nionic polyamides.