N-Spirocyclic Quaternary Ammonium Ionenes for Anion-Exchange Membranes

Abstract

The development of cationic polymers for anion-exchange membranes (AEMs) with high alkaline stability and conductivity is a considerable challenge in materials chemistry. In response, we here present the synthesis and properties of N-spirocyclic quaternary ammonium ionenes (spiro-ionenes) containing 5- and 6-membered rings fused by central nitrogen cations. High-molecular weight and film-forming spiro-ionenes are successfully synthesized in cyclo-polycondensations of tetrakis(bromomethyl)benzene and dipiperidines under mild conditions. These polyelectrolytes show excellent thermal and alkaline stability with no degradation detected by NMR spectroscopy after more than 1800 h in 1 M KOD/DO at 80 °C. Even at 120 °C, the spiro-ionenes display reasonable alkaline stability. Transparent and mechanically robust AEMs based on ionically cross-linked blends of spiro-ionene and polybenzimidazole reach OH conductivities up to 0.12 S cm at 90 °C. The current findings demonstrate that spiro-ionenes constitute a new class of alkali-stable anion-exchange polymers and membranes.

Poly(arylene alkylene)s with pendant N-spirocyclic quaternary ammonium cations for anion exchange membranes

“…In another approach, we prepared N-spirocyclic QA ionenes (spiro-ionenes) by cyclopolycondensation of tetrakis(bromomethyl)benzene and dipiperidines. 31 These polyelectrolytes showed excellent thermal and alkaline stability, with only slight degradation aer 336 h in 1 M KOD in D 2 O at 120…”

“…15 These results have inspired the preparation and study of a range of different AEMs functionalised with piperidinium [25][26][27][28][29] and spirocyclic QA cations. 13,[30][31][32][33][34][35] For example, we recently prepared poly (arylene N,N-dimethylpiperidinium)s by polycondensation of N-methyl-4-piperidone and electron-rich phenyl monomers via superelectrophilic activation in triic acid, followed by quaternisation reactions with iodomethane. 26 AEMs based on these polymers showed no structural degradation aer storage in 2 M NaOH at 60 C aer 360 h and a mere 5% ionic loss at 90 C aer the same period of time.…”

“…This nding is in good agreement with our earlier results on spiro-ionenes. 31 The introduction of a short alkyl spacer that increases exibility and allows ring relaxation signicantly increased the alkaline stability of the spiro-ionenes. The sample with the spacer showed no sign of Hofmann degradation aer 336 h immersion in 1 M KOD/D 2 O at 120 C. In contrast, the spiro-ionene without spacer still degraded through Hofmann elimination under the same conditions.…”

“…The sample with the spacer showed no sign of Hofmann degradation aer 336 h immersion in 1 M KOD/D 2 O at 120 C. In contrast, the spiro-ionene without spacer still degraded through Hofmann elimination under the same conditions. 31 Hence, distortion of ring conformations might severely reduce the advantage of the spirocyclic arrangement in comparison with a monocyclic one. Actually, the alkaline stability of the present N-spirocyclic QA cations proved to be lower than that of monocyclic N,N-dimethylpiperidinium cations of poly(arylene piperidinium)s, which showed less than 10% cationic loss aer 720 h storage in 2 M NaOH at 90 C.…”

Cross‐Linked Spirocyclic Quaternary Ammonium‐Based Anion Exchange Membrane with Tunable Properties for Fuel Cell Applications

“…The excellent alkaline stability of spirocyclic QA cation was also confirmed by theoretical calculations . Based on their determination of alkaline stability of the small molecules, the aromatic polymers with pendent spirocyclic QA and piperidinium cations have been synthesized and used to prepare AEMs . Hickner's work indicated that the backbone of AEMs have effect on the alkaline stability of cations, and the AEM has aromatic backbone with ether groups is not stable in alkaline condition.…”