Quaternized poly (2,6‐dimethyl‐1,4‐phenylene oxide) crosslinked by tertiary amine and siloxane for anion exchange membranes

Abstract

A series of tertiary amine and siloxane crosslinked composite anion exchange membranes were prepared by incorporating 2‐(3,4‐epoxycyclohexyl) ethyltrimethoxysilane (EHTMS) and N,N,N′,N′‐Tetramethyl‐1,6‐hexanediamine (TMHDA) into N‐Methyldiethanolamine (MDEA)‐functionalized poly (2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) backbone via sol‐gel process. The resultant membranes named as AEM‐X (X = 1, 2, 3, 4), which own a three‐dimensional (3D) cross‐linking structure, exhibit superior swelling resistance, mechanical properties, even the thermal stability is up to 220°C. Compared with AEM‐1 (contains no crosslinker), the swelling ratio of AEM‐2 obviously decreases by 10.2% at 80°C, while the OH− conductivity of AEM‐2 has a merely 1.9% decline (20.6 mS cm−1) at 80°C and can maintain 67% of its initial value in a 2 M aqueous NaOH at 80°C for 240 h. The simultaneous introduction of inorganic siloxane and organic linear crosslinker provides a new idea for the preparation of anion exchange membranes with largely improvement in dimensional stability and alkali resistance while the ionic conductivity is kept at comparatively high level.

Understanding ion diffusion in anion exchange membranes; effects of morphology and mobility of pendant cationic groups

“…According to scientific reports 9,23 , this issue can be attributed to the inability of AEMs to manage and maintain a uniform hydrophilic pathway inside the membranes during the service life. Among them, polyphenylene oxide (PPO) based polymers functionalized by trimethylammonium quaternary groups and their derivatives showed high alkaline stability and great ion transport properties, making them a promising candidate in fuel cell applications [24][25][26][27] . Also, recent studies have shown that PPO backbone tethered with long flexible alkyl chains (more than four carbon units) as a spacer or extenders bound to the cationic pendant group have better structural integrity and ion transport properties as compared to those without alkyl sidechains [28][29][30][31][32][33][34][35] , while the underlying mechanisms remained unclear.…”

Beneficial use of hyperbranched polymer in cross‐linked anion exchange membranes for fuel cells

“…Thus, some chemically modified PPO type polymers have been studied for AEMs, and they usually possessed excellent membrane-forming ability and enough mechnical strength. 4,32 In this work, we designed and fabricated a novel blend system comprising of a linear brominated PPO and a hyperbranched HVBC. The highly conductive and mechanically stable cross-linked networks with a loose "linear-hyperbranched" PPO-HVBC structure was expected to be constructed after the essential steps of cross-linking, quaternization and hydroxylation.…”

“…As a vital component of AEMFCs, anion exchange membranes (AEMs) play a crucial role in isolating gases and transporting ions. 4,5 Generally, AEMs are casted from the polymer electrolytes, which are usually composed of a polymer skeleton, mobile anions and functional cationic groups. [6][7][8] So far, a variety of polymers, including aromatic polymers (eg, polysulfones, polyetherketones, polyphenylene ethers, polybenzimidazoles, etc.)…”

“…As a vital component of AEMFCs, anion exchange membranes (AEMs) play a crucial role in isolating gases and transporting ions 4,5 . Generally, AEMs are casted from the polymer electrolytes, which are usually composed of a polymer skeleton, mobile anions and functional cationic groups 6‐8 .…”

Silica Containing Composite Anion Exchange Membranes by Sol–Gel Synthesis: A Short Review

“…The simultaneous uses of two cross-linking agents were intended to improve the dimensional stability and alkali resistance of the membrane and to maintain a good hydroxide conductivity, which reached 21 mS/cm at 80 °C. The alkaline stability displayed a moderate improvement [ 86 ]. Another approach based on BrPPO was exploited by He et al [ 87 ].…”