Ion transport properties of mechanically stable symmetric ABCBA pentablock copolymers with quaternary ammonium functionalized midblock. Issue 7 (7th February 2017)

• Record Type: Journal Article
• Authors: Ertem, S. Piril; Caire, Benjamin R.; Tsai, Tsung‐Han; Zeng, Di; Vandiver, Melissa A.; Kusoglu, Ahmet; Seifert, Soenke; Hayward, Ryan C.; Weber, Adam Z.; Herring, Andrew M.; Coughlin, E. Bryan; Liberatore, Matthew W.
• Is Part Of: Journal of polymer science. Volume 55:Issue 7(2017)
• Page Start: 612
• Page End: 622
• Publication Date: 2017-02-07
• Subjects: anion exchange membrane -- block copolymers -- conducting polymers -- ionomers -- ion conductivity -- inverse morphology -- morphology -- mechanical properties -- mechanically robust -- pentablock copolymer; 547
• DOI: 10.1002/polb.24310
• Languages: English
• ISSNs: 0887-6266

Abstract

ABSTRACT: Anion exchange membranes (AEMs) are a promising class of materials for applications that require selective ion transport, such as fuel cells, water purification, and electrolysis devices. Studies of structure–morphology–property relationships of ion‐exchange membranes revealed that block copolymers exhibit improved ion conductivity and mechanical properties due to their microphase‐separated morphologies with well‐defined ionic domains. While most studies focused on symmetric diblock or triblock copolymers, here, the first example of a midblock quaternized pentablock AEM is presented. A symmetric ABCBA pentablock copolymer was functionalized to obtain a midblock brominated polymer. Solution cast films were then quaternized to obtain AEMs with resulting ion exchange capacities (IEC) ranging from 0.4 to 0.9 mmol/g. Despite the relatively low IEC, the polymers were highly conductive (up to 60 mS/cm Br − at 90 °C and 95%RH) with low water absorption (<25 wt %) and maintained adequate mechanical properties in both dry and hydrated conditions. X‐ray scattering and transmission electron microscopy (TEM) revealed formation of cylindrical non‐ionic domains in a connected ionic phase. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys.2017, 55, 612–622 Abstract : Ionic block copolymers have been studied to understand structure–morphology–property relationships of ion conducting membranes. Symmetric di‐ and triblock copolymers are known to exhibit improved conductivities given their well‐defined morphologies forming nonconducting and conducting domains. At high ion concentrations, however, the nonconducting domains do not provide sufficient mechanical integrity to form robust membranes. Here, anion conductivity and mechanical properties of a midblock quaternized symmetric pentablock copolymer is presented in conjunction with investigations of the phase‐separated morphology.