Characterisation of ion transport in sulfonate based ionomer systems containing lithium and quaternary ammonium cations

Two sulfonated ionomers based on poly(triethylmethyl ammonium 2-acrylamido-2-methyl-1-propane sulfonic acid) (PAMPS) and containing mixtures of Li⁺ and quaternary ammonium cations are characterised. The first system contains Li⁺ and the methyltriethyl ammonium cation (N1222) in a 1:9 molar ratio, and the ⁷Li NMR line widths showed that the Li⁺ ions are mobile in this system below the glass transition temperature (105°C) and are therefore decoupled from the polymer segmental motion. The conductivity in this system was measured as 10^-5 Scm^-1 at 130°C. A second PAMPS system containing Li⁺ and the dimethylbutylmethoxyethyl ammonium cation (N114(2O1)) in a 2:8 molar ratio showed much lower conductivities despite a significantly lower Tg (60°C), possibly due to associations between the Li⁺ and the ether group on the ammonium cation, or between the latter cations and the sulfonate groups.