Percolated aggregates in precise sulfophenylated polyethylenes: Designing pathways to facilitate proton and ion transport

We present a set of precise, ring-opening polymerized, single-ion conducting polymers that self-assemble into percolated aggregates. These aggregates serve as pathways for rapid proton conductivity in the hydrated state (proton exchange membrane) and transport metal cations in the anhydrous state (solid polymer electrolyte). These polymers consist of a polyethylene backbone with a sulfonated phenyl group pendant on every 5^th carbon. We study this polymer in the pure acid form (p5PhSA) under hydrated conditions and fully neutralized by different counterions (p5PhSA-X, X⁺=Li⁺, Na⁺, or Cs⁺) in anhydrous conditions, using X-ray scattering, electrical impedance spectroscopy, and atomistic molecular dynamics (MD). In hydrated p5PhSA, the polymer backbone nanophase separates from the percolated acid/water domain, through which the protons travel. p5PhSA has proton conductivity of 0.28 S/cm at 40°C and 95% relative humidity, exceeding that of Nafion. The dry p5PhSA-X polymers form fully percolated ionic aggregates, and have metal cation transport decoupled from the glassy polymer backbone up to at least 180°C. This behavior results from the percolated nature of p5PhSA (-X) and demonstrates the potential of precise polymers to effectively form pathways for facilitating transport.