Fully Aromatic Ionomers with Precisely Sequenced Sulfonated Moieties for Enhanced Proton Conductivity

Abstract

A series of six fully aromatic ionomers with precisely sequenced sulfonated sites along the polymer chains have been designed, prepared, and characterized as proton-exchange membranes. Two straightforward and efficient synthetic strategies based on Ullmann ether reactions and a Baeyer–Villiger rearrangement were devised to obtain bisphenol monomers with four or six phenylene units linked exclusively by ether bridges to avoid transetherification reactions. Polycondensations of these bisphenol monomers with mono- or disulfonated dihalide monomers gave high molecular weight poly(arylene ether), poly(arylene ether sulfone), and poly(arylene ether ketone) homopolymers having microblock-like structures with sulfonated moieties separated by monodisperse nonsulfonated oligo(ether) spacers. The nanoscale morphology and properties of solvent cast membranes were closely related to the nature of the oligo(ether) spacers. Small angle X-ray scattering (SAXS) measurements showed intense scattering and very narrow ionome...