Different anion-exchange membranes (AEMs) based on polystyrene (PS)-carrying benzyltrimethyl ammonium cations are currently being developed for use in alkaline fuel cells and water electrolyzers. However, the stability in relation to these state-of-the-art cations needs to be further improved. Here, we introduce highly alkali-stable mono- and spirocyclic piperidine-based cations onto PS by first performing a superacid-mediated Friedel–Crafts alkylation using 2-(piperidine-4-yl)propane-2-ol. This is followed by quaternization of the piperidine rings either using iodomethane to produce N,N-dimethyl piperidinium cations or by cyclo-quaternizations using 1,5-dibromopentane and 1,4-dibromobutane, respectively, to obtain N-spirocyclic quaternary ammonium cations. Thus, it is possible to functionalize up to 27% of the styrene units with piperidine rings and subsequently achieve complete quaternization. The synthetic approach ensures that all of the sensitive β-hydrogens of the cations are present in ring structures to provide high stability. AEMs based on these polymers show high alkaline stability and less than 5% ionic loss was observed by ¹H NMR spectroscopy after 30 days in 2 M aq NaOH at 90 °C. AEMs functionalized with N,N-dimethyl piperidinium cations show higher stability than the ones carrying N-spirocyclic quaternary ammonium. Careful analysis of the latter revealed that the rings formed in the cyclo-quaternization are more prone to degrade via Hofmann elimination than the rings introduced in the Friedel–Crafts reaction. AEMs with an ion-exchange capacity of 1.5 mequiv g^–1 reach a hydroxide conductivity of 106 mS cm^–1 at 80 °C under fully hydrated conditions. The AEMs are further tuned and improved by blending with polybenzimidazole (PBI). For example, an AEM containing 2 wt % PBI shows reduced water uptake and much improved robustness during handling and reaches 71 mS cm^–1 at 80 °C. The study demonstrates that the critical alkaline stability of PS-containing AEMs can be significantly enhanced by replacing the benchmark benzyltrimethyl ammonium cations with N-alicyclic piperidine-based cations.

中文翻译：

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通过N脂环族哌啶基阳离子通过Friedel-Crafts烷基化对高度碱稳定的阴离子交换膜进行功能化的聚苯乙烯。

目前正在开发基于携带聚苯乙烯（PS）的苄基三甲基铵阳离子的不同阴离子交换膜（AEM），用于碱性燃料电池和水电解槽。但是，与这些最新阳离子相关的稳定性需要进一步提高。在这里，我们首先通过使用2-（哌啶-4-基）丙烷-2-醇进行超强酸介导的Friedel-Crafts烷基化，将高度碱稳定的单环和螺环哌啶基阳离子引入PS。然后使用碘代甲烷生成N，N-二甲基哌啶鎓阳离子对哌啶环进行季铵化，或分别使用1,5-二溴戊烷和1,4-二溴丁烷进行环季铵化，以获得N-螺环季铵阳离子。因此，有可能用哌啶环官能化多达27％的苯乙烯单元，随后实现完全季铵化。合成方法可确保阳离子的所有敏感β-氢均存在于环结构中，以提供高稳定性。基于这些聚合物的AEM在90°C下在2 M NaOH水溶液中放置30天后，通过¹ H NMR光谱显示出较高的碱性稳定性和小于5％的离子损失。用N，N-二甲基哌啶鎓阳离子官能化的AEM表现出比带有N-螺环季铵盐的AEM高的稳定性。对后者的仔细分析表明，在环季铵化反应中形成的环更容易降解通过霍夫曼消除，比在Friedel-Crafts反应中引入的环要强。在完全水合条件下，离子交换容量为1.5 mequiv g ^–1的AEM在80°C时达到106 mS cm ^–1的氢氧化物电导率。通过与聚苯并咪唑（PBI）共混，可以进一步调整和改进AEM。例如，含有2 wt％PBI的AEM在处理过程中显示出减少的吸水率和坚固性，并在80°C时达到71 mS cm ^–1。该研究表明，通过将N-脂环族哌啶基阳离子替代基准苄基三甲基铵阳离子，可以显着提高含PS的AEM的关键碱性稳定性。