Durability and performance of polystyrene-b-poly(vinylbenzyl trimethylammonium) diblock copolymer and equivalent blend anion exchange membranes

Anion exchange membranes (AEM) are solid polymer electrolytes that facilitate ion transport in fuel cells. In this study, a polystyrene-b-poly(vinylbenzyl trimethylammonium) diblock copolymer was evaluated as potential AEM and compared with the equivalent homopolymer blend. The diblock had a 92% conversion of reactive sites with an IEC of 1.72 ± 0.05 mmol g⁻¹, while the blend had a 43% conversion for an IEC of 0.80 ± 0.03 mmol g⁻¹. At 50°C and 95% relative humidity, the chloride conductivity of the diblock was higher, 24–33 mS cm⁻¹, compared with the blend, 1–6 mS cm⁻¹. The diblock displayed phase separation on the length scale of 100 nm, while the blend displayed microphase separation (∼10 μm). Mechanical characterization of films from 40 to 90 microns thick found that elasticity and elongation decreased with the addition of cations to the films. At humidified conditions, water acted as a plasticizer to increase film elasticity and elongation. While the polystyrene-based diblock displayed sufficient ionic conductivity, the films' mechanical properties require improvement, i.e., greater elasticity and strength, before use in fuel cells. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 41596.