Fully aromatic ionomers with precisely sequenced sulfonated moieties for enhanced proton conductivity

• Abstract in UndeterminedA 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 straight-forward 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 polyarylene ether ketone) homopolymers having microblock-like structures with sulfonated moieties separated by monodisperse non-sulfonated 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 ionomer peaks with second-order features for the polymers with the six-ring spacers. This clearly indicated that the controlled ionic sequencing enabled self-assembly of ionic aggregates with a much higher degree of organization in relation to a corresponding aromatic ionomer with a statistical distribution of the sulfonate groups. At an identical acid content, the ionomers containing meta ether linkages had lower glass transition temperatures than the all-para materials, leading to a higher water uptake and proton conductivity of the former ionomers. A membrane with an ion exchange capacity (IEC) of 2.05 meq g-1 and containing exclusively para linkages reached the same level of proton conductivity as Nafion® at 100% relative humidity (RH), and also had an excellent dimensional stability in boiling water. Under reduced RH, the conductivity of this membrane greatly exceeded that of a membrane based on a statistical copolymer analogue with a similar ionic content.

Ämnesord

NATURVETENSKAP  -- Kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences (hsv//eng)

Nyckelord

fuel cells

polymer electrolyte membranes

aromatic block copolymers

sequence-controlled polymerizations

SAXS

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