| Résumé | The proton conductivity of solvent-cast proton exchange membranes (PEM) prepared from sulfonated poly(ether ether ketone) (SPEEK) was found to be sensitive to the choice of casting solvent and the membrane drying conditions. Using proton nuclear magnetic resonance (NMR) spectroscopy, several factors were shown to affect proton conductivity in PEMs. NMR revealed the formation of strong interactions between SPEEK polymer and the casting solvents dimethylformamide (DMF) and dimethylacetamide (DMAc), commonly used in PEM preparation. DMF readily hydrogen-bonds with the polymers' sulfonic acid groups starting at temperatures as low as 60 C. However, DMAc is much less susceptible to hydrogen bonding, which occurs only above 100 C. Both DMF and DMAc solvent interactions with SPEEK during PEM preparation significantly affect the proton conductivity properties. In addition, both solvents are prone to thermal decomposition resulting in dimethylamine which also strongly hydrogen-bonds with SPEEK. The presence of residual sulfuric acid originating from SPEEK preparation has a catalytic effect on the thermal degradation of DMF and DMAc. Under high temperature treatment of films, residual sulfuric acid reacts with both DMF and DMAc, causing their degradation resulting in the formation of N,N-dimethylaminium hydrogensulfate which is also believed to have a negative effect on proton conductivity. |
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