Ion transport and aggregate morphology in precise sulfophenylated polyethylene ionomers*

A set of new and amorphous precise ionomers synthesized by ring-opening polymerization exhibit decoupled ion transport. 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 (X is 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 200°C. Distance between aggregates appears independent of ion type, with an interaggregate spacing of ~1.9 nm present in the Li⁺, Na⁺, and Cs⁺ as-cast ionomers. Atomistic molecular dynamics simulations are used to elucidate the structure of aggregates in the ionomers and compared to absolute X-ray scattering data. The ionomers exhibit conductivity of 10^-8 to 10^-7 S/cm at 150°C. These materials demonstrate decoupled ion transport up to 200°C, a result of ions traveling within ionic aggregates and independent of chain dynamics.