Synthesis and properties of a new ether-free poly(bis-alkylpiperidinium) polymer for the anion exchange membrane

Developing anion exchange membranes (AEMs) with high performance and excellent alkaline stability is a huge challenge to the fuel cell. Herein, a new bispiperidinium compound is synthesized through a nucleophilic reaction between 4,4′-trimethylenebis (1-methyl piperidine) and 4-bromomethylbiphenyl. Subsequently, a novel poly(bis-alkylpiperidinium) polymer (i.e. Tmmp-Bmb-TFAc) is synthesized through the Friedel-Crafts polycondensation of bispiperidinium monomer and 1,1,1-trifluoroacetone. The synthesized ether-free Tmmp-Bmb-TFAc contains two piperidinium cations per polymer repeat unit in the main chain, which thus is employed as the AEM. The obtained AEM exhibits high ionic exchange capacity of 2.25 mmol g−1, low volume swelling of 13.6% and moderate tensile strength of 12.3 MPa in Br- form simultaneously. Meanwhile, the Tmmp-Bmb-TFAc membrane achieves a high conductivity of 45.0 mS cm−1 at 80 °C and possesses an excellent alkaline stability in 1 mol L−1 KOH at 60 °C within 480 h. Furthermore, no degradation of the polymer backbone is detected by 1H NMR spectra when immersing the membrane in 1 mol L−1 KOH at 80 °C. This work provides a gentle and facile approach on the design and preparation of ether-free AEMs with cations in the polymer main chain.