Proton transport through acid aggregates in a hydrated precise sulfophenylated polyethylene*

Hydrated acid aggregates in a precise sulfophenylated polyethylene exhibit high proton conductivity. This study focuses on a new precise polymer, synthesized by ring-opening polymerization, that has a polyethylene backbone with a sulfonated phenyl group pendant on every 5^th carbon, p5PhSA. The structure of p5PhSA is characterized with X-ray scattering and the proton conductivity is characterized with electrical impedance spectroscopy. Both experiments are performed as a function of relative humidity and temperature. Sorption measurements determined the water uptake in p5PhSA as a function of humidity as well. Atomistic molecular dynamics simulations are used to elucidate the structure of the acid aggregates in the amorphous polymer matrix and are directly compared to absolute X-ray scattering data. At 40°C and 90% relative humidity, the proton conductivity of p5PhSA is 0.17 S/cm, exceeding that of Nafion. At room temperature, interaggregate distance nearly doubles from 1.8 nm at 0% relative humidity, to 3.4 nm at 100% relative humidity. The swelling of these ordered acid aggregates with water is reversible, and facilitates the proton transport through p5PhSA.