Poly(N,N-diallylazacycloalkane)s for anion-exchange membranes functionalized with N-spirocyclic quaternary ammonium cations

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Abstract

The alkaline stability of organic cations tethered to anion-exchange membranes (AEMs) is essential for the long-term performance of alkaline membrane fuel cells and electrolyzers. Here, we have prepared and studied the thermal and alkaline stability of a series of polyelectrolytes functionalized with N-spirocyclic quaternary ammonium (QA) cations. N,N-diallyl azacycloalkane quaternary salts were readily synthesized by diallylation of pyrrolidine, piperidine, azepane, and morpholine, respectively. These monomers were employed in radical-initiated cyclo-polymerizations to obtain the target poly(N,N-diallyl azacycloalkane)s. 1H NMR spectroscopy revealed that the stability of the polyelectrolytes in 2 M KOD/D2O solutions critically depended on the ring size and the absence of additional heteroatoms in the ring. Thus, poly(N,N-diallyl piperidinium) showed the highest alkaline stability, with only minor signs of degradation at 120 °C after 14 days, while the polyelectrolytes based on the morpholine and azepane rings clearly degraded via both Hofmann elimination and ring-opening substitution already at 90 °C. Crosslinked water non-soluble AEMs were prepared by copolymerizing N,N-diallyl piperidinium chloride with methylbenzyldiallyl ammonium groups tethered to poly(phenylene oxide). These transparent and mechanically robust AEMs reached high OH conductivities, above 0.1 S cm-1 at 80 °C. The present work demonstrate the high alkaline stability of suitably configured N-spirocyclic QA cations, which will open up new prospects for readily accessible high performance polyelectrolytes and membranes.

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Subject classification (UKÄ) – MANDATORY

  • Engineering and Technology
  • Polymer Chemistry
  • Polymer Technologies
  • Energy Systems
Original languageEnglish
Pages (from-to)2784-2793
JournalMacromolecules
Volume50
Issue number7
Publication statusPublished - 2017
Publication categoryResearch
Peer-reviewedYes

Bibliographic note

Publication Date (Web): March 31, 2017