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

• Published in: Macromolecules 2011-08, Vol.44 (15), p.5937-5946
• Main Authors: Zhang, Min, Kim, Hyung Kyu, Chalkova, Elena, Mark, Fedkin, Lvov, Serguei N, Chung, T. C. Mike
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Organic polymers; Physicochemistry of polymers; Polymer industry, paints, wood; Polymers with particular properties; Preparation, kinetics, thermodynamics, mechanism and catalysts; Technology of polymers
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma200836d

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 [C x N(SiMe3)2], with or without styrenic diene (cross-linker), to form ethylene/C x N(SiMe3)2 copolymers and ethylene/C x N(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/C x N(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.