Gyroid and Other Ordered Morphologies in Single-Ion Conducting Polymers and Their Impact on Ion Conductivity

Lu Yan, Christina Rank, Stefan Mecking, Karen I. Winey J. Am. Chem. Soc. 2019, DOI:10.1021/jacs.9b09701

Abstract: Controlling the self-assembled nanoscale ionic aggregates in single-ion conducting polymers is a crucial step toward exceptional transport properties. We report a series of precisely-segmented polyethylene-like ionomers containing sulfonate groups (PES23) with Li+, Na+, Cs+, or NBu4+ counterions synthesized from step-growth polymerization. At room temperature, all polymers are semicrystalline with well-def̅ined nanoscale ionic layers separated by 35-38 Å, depending on the cation. In situ X-ray scattering measurements reveal that the layered ionic aggregates in PES23Li, PES23Na, and PES23Cs transform, upon melting the PE blocks, into the 3 gyroid morphology. The gyroidal ionic aggregates in PES23Li and PES23Na further evolve into hexagonal symmetry as the temperature increases. These order-to-order transitions in ionic aggregate morphologies were also confirmed by oscillatory shear rheology. The ion transport behavior of these PES23 polymers is strongly dependent on the ionic aggregate morphologies. Specifically, the 3D interconnected gyroid morphology of PES23Li exhibits higher ionic conductivity than the isotropic layered or hexagonal morphologies. This innovative and versatile molecular design of ionomers leads to unprecedented percolated gyroidal ionic aggregate morphologies that provide a continuous pathway for improved ion transport.