Backbone Chemistry Determines Ion Dissociation and Nanostructure Morphology in Charged-Neutral Blends with Low-Molecular-Weight PEO

Abstract

Charged-neutral polymer blends provide a versatile platform for controlling ion dissociation, nanoscale organization, and thermodynamic behavior through polymer chemistry, making them attractive materials for applications ranging from ion-containing soft matter to single-ion polymer electrolytes. Here, we systematically investigate blends of low-molecular-weight poly(ethylene oxide) (PEO, Mw ≈ 0.5 kg mol–1) with two NaTFSI-based polyanions possessing chemically distinct backbones: polar poly(methacrylate) (PMATFSINa) and nonpolar polystyrene (PSTFSINa). By combining SAXS/WAXS, DSC, and Raman spectroscopy, we establish a direct correlation between polymer backbone chemistry, ion dissociation, morphology, and thermal behavior. PMATFSINa/PEO blends achieve ∼70% TFSI– dissociation (Raman), molecular-level miscibility accompanied by disruption of ionic aggregates (SAXS/WAXS), and rapid PEO crystallinity suppression (Xc → 0 by ∼40 wt % polyanion; DSC), yielding elevated Tg at low loadings from strong ion–dipole constraints. PSTFSINa/PEO blends exhibit ∼20–30% dissociation, hierarchical mesoscale heterogeneity (persistent aggregates + nanoscale correlations), PEO crystallinity persisting to ∼40 wt % polyanions, and Tg crossover at higher loadings driven by rigid PS domains. These findings demonstrate that polymer backbone chemistry dictates ion dissociation, which in turn governs nanoscale organization and thermal behavior, establishing molecular-level design principles for charged–neutral polymer blends and their application as single-ion polymer electrolytes.