Percolated ionic aggregates in precise sulfophenylated polyethylene ionomers: Morphology and ion transport*

We present a set of precise single-ion conducting ionomers that demonstrate decoupled transport of metal cations within self-assembled percolated aggregates in glassy polymer matrices. These precise ionomers consist of a polyethylene backbone with a sulfonated phenyl group pendant on every 5^th carbon, that is fully neutralized by a counterion X (Li⁺, Na⁺, or Cs⁺), p5PhSA-X. The morphologies of these ionomers are characterized with X-ray scattering, and the ion transport properties are characterized with electrical impedance spectroscopy. Both experiments are performed under vacuum, from room temperature up to 180°C. Atomistic molecular dynamics simulations elucidate that the structure of the aggregates in the ionomers is a percolated network. The characteristic length scales of these percolated aggregates as measured by X-ray scattering are ~2nm and independent of ion type. There is good agreement between simulations and experimental X-ray scattering data. The ionomers exhibit conductivity of 10^-7 to 10^-6 S/cm at 180°C and demonstrate Arrhenius behavior up to 180°C. This indicates that the ion transport is decoupled from the polymer backbone, which is consistent with a percolated aggregate within which ions travel.