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

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Abstract

Abstract in Undetermined
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 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.

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Subject classification (UKÄ) – MANDATORY

  • Chemical Sciences

Keywords

  • fuel cells, polymer electrolyte membranes, aromatic block copolymers, sequence-controlled polymerizations, SAXS
Original languageEnglish
Pages (from-to)1447-1459
JournalMacromolecules
Volume45
Issue number3
Publication statusPublished - 2012
Publication categoryResearch
Peer-reviewedYes

Bibliographic note

Publication Date (Web): January 23, 2012 The information about affiliations in this record was updated in December 2015. The record was previously connected to the following departments: Polymer and Materials Chemistry (LTH) (011001041)