Alkaline stability of model anion exchange membranes based on poly (phenylene oxide) (PPO) with grafted quaternary ammonium groups: Influence of the functionalization route
Alkaline stability of model anion exchange membranes based on poly (phenylene oxide) (PPO) with grafted quaternary ammonium groups: Influence of the functionalization route
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DOI：
10.1016/j.polymer.2019.121931
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发表时间：
2019-12-17
期刊：
影响因子：
4.6
通讯作者：
Di Vona, M. L.
中科院分区：
文献类型：
--
作者：
Becerra-Arciniegas, R-A;Narducci, R.;Di Vona, M. L.
我们研究了侧甲基对基于接枝三甲基铵基团的聚（2,6-二甲基-1,4-亚苯基）氧化物（PPO）的模型阴离子交换聚合物的碱性稳定性的影响。聚合物主链通过不同的合成程序进行修饰：通过溴化途径，离聚物铵基团插入到 PPO 的结构甲基上 (Br-PPO-TMA)，而通过氯甲基化途径，铵基团在邻位连接到 PPO 的甲基基团 (Cl-PPO-TMA)。通过 NMR 和 FTIR 光谱、热重分析、吸水率、机械拉伸测试、小角 X 射线散射 (SAXS) 和阻抗谱研究膜的性能。 SAXS 分析表明 Cl-PPO-TMA 具有更好的纳米相分离，这与稍大的吸水率和离子电导率一致。还比较了两种聚合物在 80 ℃ 2 M NaOH 中老化不同时间前后的性能。热重分析显示碱处理后铵基团损失和主链醚裂解。通过溴化路线制备的样品显示出更高的离子电导率稳定性，这可能是由于铵基团的碱性攻击减少，尽管DFT计算没有显示热力学和动力学反应参数的主要差异。碱处理后，Br-PPO-TMA 化合物的机械性能下降较多。机械性能的下降可归因于醚键的碱性断裂导致 PPO 平均链长的减少。两种合成路线都有优点和缺点，但氯甲基化制备的样品具有更高的重现性和更好的机械性能被认为是最主要的优点。
We study the effect of pendent methyl groups on the alkaline stability of model anion exchange polymers based on poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) with grafted trimethylammonium groups. The polymer backbone is modified varying the synthesis procedure: by the bromination route, the ionomeric ammonium groups are inserted on the structural methyl group of PPO (Br-PPO-TMA), while by the chloromethylation route the ammonium groups are attached in the ortho-position to the methyl group of PPO (Cl-PPO-TMA). The properties of the membranes are studied by NMR and FTIR spectroscopy, thermogravimetry, water uptake, mechanical tensile tests, small-angle X-ray scattering (SAXS) and impedance spectroscopy. SAXS analysis indicates a better nanophase separation for Cl-PPO-TMA, which is consistent with a slightly larger water uptake and ionic conductivity. The properties of the two polymers are also compared before and after the aging in 2 M NaOH at 80 degrees C for different times. The thermogravimetric analysis shows the loss of the ammonium groups and the backbone ether cleavage after alkali treatments. The samples prepared by the bromination route show a higher stability of ionic conductivity, presumably due to a reduced alkaline attack of the ammonium groups, although DFT calculations do not show major differences of thermodynamic and kinetic reaction parameters. After alkaline treatment, the mechanical properties are more degraded for the Br-PPO-TMA compound. The decreased mechanical properties can be attributed to a reduction of the average chain length of PPO by alkaline scission of the ether links. Both synthesis routes have advantages and disadvantages, but the higher reproducibility and the better mechanical properties of samples prepared by chloromethylation are considered preponderant benefits.