Poly­(ethylene oxide) [PEO] ionomers are candidate materials for electrolytes in energy storage devices due to the ability of ether oxygen atoms to solvate cations. Copolyester ionomers are synthesized via condensation of sulfonated phthalates with glycol mixtures of PEO and poly­(tetramethylene oxide) [PTMO] to create random copolymer ionomers with nearly identical ion content and systematically varying solvation ability. Variation of the PEO/PTMO composition leads to changes in T g, dielectric constant and ionic aggregation; each with consequences for ion transport. Dielectric spectroscopy is used to determine number density of conducting ions, their mobility, and extent of aggregation. Conductivity and mobility display Vogel temperature dependence and increase with PEO content; despite the lower T g of PTMO. Conducting ion densities show Arrhenius temperature dependence and are nearly identical for all copolymer ionomers that contain PEO. SAXS confirms the extent of aggregation, corroborates the temperature response from dielectric measurements, and reveals microphase separation into a PTMO-rich microphase and a PEO-rich microphase that contains the majority of the ions. The trade-off between ion-solvation and low T g in this study provides fundamental understanding of ionic aggregation and ion transport in polymer single-ion conductors.

Random ionomers based on methacryl poly-(ethylene oxide) with nine ethylene oxide units on the side chain and sodium sulfonated styrene (NaSS) are synthesized by reversible addition−fragmentation chain transfer polymerization. The glass transition temperature increases gradually as ions are incorporated at low ion content then more strongly as the ion content reaches 51 mol % NaSS comonomer (1:9 ion to ether oxygen (EO) ratio), exceeding the polarizability volume overlap for contact pairs at 35 mol % NaSS comonomer. Ionomers with 51 and 70 mol % NaSS comonomer show microphase separation, as determined by X-ray scattering, where ion-rich microphases have glass transition temperature T g = 165 °C excluding many of the PEO side chains, which primarily reside in a dilute ion-pair microphase. Fourier transform infrared spectroscopy was used to characterize the fraction of sulfonates in three different association states that can be related to the static dielectric constant from dielectric relaxation spectroscopy through the Onsager equation. The ionomer with 10 mol % NaSS comonomer exhibits the highest room-temperature conductivity (∼10 −7 S/cm) that results from the best combination of number density of simultaneously conducting ions and their mobility, with no ion-rich microphase below 100 °C.

Lithium ion conduction is investigated for a polysiloxane-based single-ion conductor containing weak-binding borates and cyclic carbonate side chains, plasticized with poly(ethylene glycol) (PEG). The addition of PEG increases the conductivity by up to 3 orders of magnitude compared to the host ionomer. A physical model of electrode polarization is used to separate ionic conductivity of the ionomers into number density of simultaneously conducting ions and their mobility. A reduction in T g with increasing PEG content boosts ion mobility owing to an increase in polymer chain flexibility. Further, the PEG ether oxygens lower the activation energy of simultaneously conducting ions (from 14 to 8 kJ/mol), significantly increasing conducting ion content by 100X, suggesting that ion aggregates observed in the host ionomer are solvated by PEG. This directly reflects the disappearance of an ion aggregation peak observed in X-ray scattering, and an initial large increase in static dielectric constant (ε s ), upon addition of PEG, suggesting that ionic aggregation is significantly reduced by a small amount of PEG. Further dilution with lower dielectric constant PEG gradually reduces ε s .

Polysiloxane phosphonium single-ion conductors grafted with oligomeric PEO and with ion contents ranging from 5 to 22 mol % were synthesized via hydrosilylation reaction. The parent Br − anion was exchanged to F − or bis-(trifluoromethanesulfonyl)imide (TFSI − ). X-ray scattering data suggest ion aggregation is absent in these phosphonium ionomers, which contributes to low glass transition temperatures (below −70 °C) with only a weak dependence on both ion content and counteranion type. Conductivities weakly increase with ion content but exhibit a strong dependence on anion type. The highest conductivity at 30 °C is 20 μS/cm for dry neat ionomer, with the TFSI − anion, consistent with its relatively delocalized negative charge and large size that weaken interactions between TFSI − and the phosphonium cation.

Poly(ethylene glycol) plasticizer is blended with a PEO-based single-ion conductor to lower the glass transition temperature of the ionomer and solvate the lithium counterions. With increasing plasticizer content at room temperature, FTIR spectra indicate that the fraction of ions in isolated ion pairs increases relative to those in ionic aggregates, and X-ray scattering data