Molecular Mobility and Cation Conduction in Polyether–Ester–Sulfonate Copolymer Ionomers

Abstract

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.

Block copolymer electrolytes for rechargeable lithium batteries

“…PEO has been studied extensively as a promising candidate for polymer electrolytes due to its low glass transition temperature ( T g ), which promotes charge transport, and good ability to dissolve lithium salts . The ion transport in PEO:salt complexes is assisted by segmental motion of PEO chains in the amorphous state.…”

Dynamic cross-links to facilitate recyclable polybutadiene elastomer with excellent toughness and stretchability

“…Ionomers are polymers containing a relatively small amount (up to 10–15 mol %) of ionic groups in the polymer backbone . The ionic aggregates can act as physical cross‐links resulting in unique physical properties, such as enhanced mechanical strength and miscibility . Another important property of ionomers is their thermoplastic behavior due to the thermally reversible ionic cross‐links, thus allowing the facile processing of polymers at elevated temperature, known as ionic thermoplastic elastomers .…”

Transient Metallosupramolecular Networks Built from Entangled Melts of Poly(ethylene oxide)

“…19,20 The terminal relaxation time of the glassy plateau can also increase with the ion content, as it has been observed for example in unentangled PEO−Li + and PEO−Na + . 14,16 Furthermore, the conductivity in these systems was shown to be a direct function of the glass transition of the polymer, which determines the segmental mobility at the application temperature as well as mobility and density of conducting cations. 14 It is understood that the ion hopping process can alter the molecular motion of the chains by acting as temporary topological constraints.…”

“…14,16 Furthermore, the conductivity in these systems was shown to be a direct function of the glass transition of the polymer, which determines the segmental mobility at the application temperature as well as mobility and density of conducting cations. 14 It is understood that the ion hopping process can alter the molecular motion of the chains by acting as temporary topological constraints. 21−23 Despite numerous investigations on PEO with alkali and alkaline-earth metal salts, the complexation of PEO with transition metal ions is rarely studied.…”