Angela Mohanty - Stable Elastomeric Anion Exchange Membranes Based on Quaternary Ammonium-Tethered SEBS Triblock Copolymers

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Mohanty, A.D.; Kim, Y.S.; and Bae, C., Stable Elastomeric Anion Exchange Membranes Based on Quaternary Ammonium-Tethered SEBS Triblock Copolymers,Macromolecules, 2015, 48, 7085

  Abstract:

 A chemically stable and elastomeric triblock copolymer, polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene

(SEBS), was functionalized with various benzyl- and alkyl-substituted quaternary ammonium (QA) groups for anion exchange

membrane (AEM) fuel cell applications. Synthetic methods involving transition metal-catalyzed CH borylation and Suzuki

coupling were utilized to incorporate six diff erent QA structures to the polystyrene units of SEBS. Changes in AEM properties as

a result of diff erent QA moieties and chemical stability under alkaline conditions were investigated. Anion exchange polymers

bearing the trimethylammonium pendants, the smallest QA cation moiety, exhibited the most signifi cant changes in water uptake

and block copolymer domain spacing to off er the best ion transport properties. It was demonstrated that incorporating stable

cation structures to a polymer backbone comprising solely CH and CC bonds resulted in AEM materials with improved longterm

alkaline stability. After 4 weeks in 1 M NaOH at 60 and 80  ° C, SEBS-QA AEMs remained chemically stable.   Fuel cell tests

using benzyltrimethylammonium-containing SEBS (SEBS-TMA) as an AEM demonstrated excellent performance, generating

one of the best maximum power density values and lowest ohmic resistance with low Pt catalyst loaded electrode reported thus

   

far. Both polymer backbone and cation functional group remained stable after 110 h lifetime test at 60 °C.

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