Structure-Property Relationships in Solvent-Swollen Sulfonated Polystyrene Ionomers

The strong coupling of ion transport to polymer segmental dynamics limits the use of polymers in applications such as lithium-ion batteries. Selectively swelling nanostructured single ion-containing polymers with solvents could tune ionic interactions, enhance segmental dynamics, and provide alternative mechanisms for improved ion transport. Without solvent, sulfonated polystyrene copolymers display a range of ionic aggregate morphologies (discrete aggregates, co-continuous structures, etc.) and segmental dynamics as a function of degree of sulfonation. To develop structure-property relationships upon solvent swelling, we incorporate organic solvents into lightly and moderately sulfonated polystyrene ionomers neutralized with lithium counterions. The influence of ion exchange capacity, solvent chemistry, solvent physical properties, and solvent content are investigated. Small- and wide-angle X-ray scattering captures morphological changes upon swelling, and broadband dielectric spectroscopy measures the characteristic relaxation timescales and ionic conductivities. These findings provide insights for designing polymer chemistries, polymer morphologies, and solvent identities to enhance ion transport.