Ion Transport in Precise Sulfonate Ionomers with Layered, Cylindrical, and Gyroid Morphologies

Precise spacing of ionic pendant groups along linear polymers produces well-defined nanoscale ion-aggregate morphologies and allows new insights into the ion transport mechanism. In this study, we investigate a series of new ionomers synthesized by polycondensation having sodium (Na⁺) or tetrabutylammonium ([N(C₄H₉)₄]⁺) sulfosuccinate segments precisely placed every 23 or 48 backbone carbons of a linear backbone. X-ray scattering studies suggest that these precise semicrystalline ionomers containing sodium sulfosuccinate segments form layered or bicontinuous cubic gyroid ionic nanochannels at room temperature and transition to hexagonal symmetry upon heating. In contrast, those containing tetrabutylammonium sulfosuccinate segments exhibit layered ionic aggregates and transition to liquid-like morphologies upon heating. The temperature dependence of ion transport includes both VFT and Arrhenius behavior and varies with ion aggregate morphology. Overall, increasing cation size from Na⁺ to [N(C₄H₉)₄]⁺ leads to faster ion transport due to the enhanced ion dissociation. These precise ionomers provide a promising way to design solid polymer electrolytes with interconnected ionic nanochannels for fast ion transport.

We acknowledge NSF Grant DMR (15-06726).