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 + or - 0.05 mmol g-1, while the blend had a 43% conversion for an IEC of 0.80 + or - 0.03 mmol g-1. At 50oC 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 (approximately 10 micrometers). 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. Published in Applied Polymer Science, v132 n10 article 41596 p1-9, 2015. Sponsored in part by ARO, grant no. W911NF-11-1-0462. The original document contains color images.