Synthesis of Anion Exchange Membranes with Side-Chain-Type Benzylic Cationic Groups Using Chloromethylbenzoylation

Abstract

To circumvent the shortcomings of traditional synthetic routes relying on chloromethylation or bromination of benzylic methyl groups, a novel approach, chloromethylbenzoylation, has been proposed to synthesize commercially available poly(aryl ether)s (PAEs) with side-chain-type benzylic cationic groups for anion exchange membranes (AEMs). Previous works have demonstrated that adding alkyl side chain to PAE backbones can improve the alkaline stability of the AEMs. In this work, side-chain-type benzylchloride groups have been directly introduced onto poly resorcinol ketone (PRK) via an acylation reaction between 4-(chloromethyl)benzoic acid and PRK in P2O5/CH3SO3H at 60 oC. 1H NMR and GPC confirm that 100% substitution occurred, without side reactions such as crosslinking or degradation. Robust AEMs were then obtained through amination upon introduction of trimethylammonium (TMA+) groups. The chloride ionic conductivity of the AEM was 8.8 mS/cm at 30 °C, which is competitive with that of a commercial TokuyamaÒ A201 membrane at similar IEC values. In summary, this approach represents a simple and straightforward route capable of quantitative introduction of side-chain-type benzylchloride groups without using expensive or toxic reagents, with potential applications of the resultant AEMs in energy conversion and storage and other fields.