The conductivity and physical properties of the ion conductive channels in a multiblock copoly(arylene ether) polymer was quantitatively measured as a function of (i) block size, (ii) number of tethered head-groups per polymer repeat unit and (iii) type of cation head-groups. Multiblock copoly(arylene ether)s with 1, 2, 3 and 4 alkyl chain tethered quaternary ammonium head-groups on each hydrophilic repeat unit. Synthesis was by polycondesation, Friedel-Crafts, and reduction reactions. The effect of the number of ionic groups on the ion exchange capacity (IEC), morphology and properties of the anion exchange membranes was investigated. As the ionic group density increased, both the ionic conductivity and water uptake of the membranes increased. The 3-tether membrane formed the most efficient ionic channels as determined by the highest ionic conductivity/IEC. The 2, 3, and 4-tether (per hydrophilic repeat unit) membranes had 9 to 10 bound waters of hydration per ionic group pair. The optimum membrane had three head-groups per hydrophilic repeat unit (X3Y5-3): 130.6 mS/cm ionic conductivity at 80oC, 58.3% water uptake, IEC of 1.83 meq/g. All the membranes showed acceptable thermal stability and alkaline stability in 1 M KOH at 60oC for 1000 h. As the number of head-groups per hydrophilic repeat unit increased, the mechanical strength of the membranes decreased. The two-tether (per hydrophilic repeat unit) block copolymer was used to compare three previously reported head-groups: quaternary trimethylammonium, quinuclidium, and tris(2,4,6-trimethoxyphenyl)phosphonium cations in terms of size of the conducting channels, ionic conductivity of the mobile hydroxide ion, mechanical properties, quantity of productive and unproductive water, and chemical stability of the membrane in base. The interdomain spacing acquired from small angle X-ray scattering showed that multiblock copolymers with larger cations formed larger ion conduction channels in the membrane, however, the larger channel size was not an advantage. The morphology and membrane properties of films quaternized before casting were compared to membranes quaternized after casting.

Conductive channel architecture in anion conducting multiblock copolymers

256th National Meeting (2018)

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