Thin, robust, and chemically stable photo-cross-linked anion exchange membranes based on a polychlorostyrene-b-polycyclooctene-b-polychlorostyrene ABA triblock polymer

A polychloromethylstyrene-b-polypolycyclooctene-b-polychloromethylstyrene ABA triblock polymer was used as a backbone in a study to produce a chemically and mechanically robust anion exchange membrane (AEM). The material is easily scalable and the polypolycyclooctene segment (low Tm) makes the membrane flexible to handle. Comparison of the non-crosslinked triblock polymer functionalized with different cations namely; piperidinium, pyrrolidinium, tris(2,4,6-trimethoxyphenyl) phosphonium, and the benchmark trimethylammonium cation showed that the piperidinium functionalized membrane with an ionic exchange capacity of ca. 1.36 mmol.g− 1 had the highest OH− conductivity ca. 95 mS·cm− 1 at 80 °C, 95% RH, and the highest Cl− conductivity of ca. 31 mS·cm− 1 at 70 °C, 95% RH. The membrane with the piperidinium cation was the most chemically stable when immersed in 1 M KOH at 80 °C (with only 16% degradation after 14 days) compared to all the other cation functionalized membranes studied here. Photo-crosslinking with 1,10-decanedithiol (DT) eliminated the melting behavior of the polycyclooctene black and improved the mechanical stability of the films allowing < 20 μm large area transparent membranes to be produced. The DT cross-linking reduced the membrane swelling on all length scales as shown by small angle X-ray scattering, water uptake, and dimensional swelling data, and allowed the membrane to be fully intact even at fully hydrated states based on the tensile strength measurements.