New Polyethylene Based Anion Exchange Membranes (PE–AEMs) with High Ionic Conductivity

By Zhang, Min; Kim, Hyung Kyu; Chalkova, Elena; Mark, Fedkin; Lvov, Serguei N. & Chung, T. C. Mike
Published in Macromolecules NULL 2011

Abstract

This paper discusses a new class of high performance polyethylene-based anion exchange membranes (PE -AEMs) that contain a wide concentration range of pendant (flexible) ammonium chloride (NR3+Cl -) groups and with or without a cross-linked PE matrix structure. The chemistry involves a metallocene-mediated polymerization of ethylene, silane-protected α,ω-amino-olefin [CxN(SiMe3)2], with or without styrenic diene (cross-linker), to form ethylene/CxN(SiMe3)2 copolymers and ethylene/CxN(SiMe3)2/diene terpolymers, respectively. The resulting co- and ter-polymers were completely soluble in common organic solvents and were solution-casted into uniform films (thickness, 50 -70 μm; without backing material) and then thermal cross-linked in ethylene/CxN(SiMe3)2/diene case, further interconverting the silane-protected amino groups into the desired -NR3+Cl - groups (R: H, CH3, and C3H7) under solid state conditions. The resulting PE -NR3+Cl - and cross-linked x-PE -N(CH3)3+Cl - membranes were systematically studied to understand how the PE structure (-NR3+Cl - concentration, R group, cross-linking density, etc.) affects ionic conductivity, water uptake, film stability, and ion selectivity. For comparison, several commercially available AEMs were also examined. Evidently, an x-PE -N(CH3)3+Cl - membrane, with 28.1 mol % -N(CH3)3+Cl - groups and 0.2 mol % cross-linkers, shows moderate water swelling and outperforms all commercial membranes with exceptionally high ionic conductivities of 119.6 mS/cm in 2 N HCl solution and 78.8 mS/cm in 2 N HCl -0.2N CuCl solution at room temperature.

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