Fully aromatic ionomers with precisely sequenced sulfonated moieties for enhanced proton conductivity
Author
Summary, in English
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.
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.
Department/s
Publishing year
2012
Language
English
Pages
1447-1459
Publication/Series
Macromolecules
Volume
45
Issue
3
Links
Document type
Journal article
Publisher
The American Chemical Society (ACS)
Topic
- Chemical Sciences
Keywords
- fuel cells
- polymer electrolyte membranes
- aromatic block copolymers
- sequence-controlled polymerizations
- SAXS
Status
Published
ISBN/ISSN/Other
- ISSN: 0024-9297