Proton Mobility in Sulfonated PolyEtherEtherKetone (SPEEK): Influence of Thermal Crosslinking and Annealing

Sulfonated PolyEtherEtherKetone (SPEEK) was thermally treated at 180 and 140 degrees C to study the effects of polymer cross-linking and annealing on the water uptake and proton conductivity. The kinetics of the cross-linking reaction can be quantitatively described with an activation energy of (100 +/- 2)kJ/mol. The proton mobility u(H+) depends on the proton concentration c(H+) in excellent agreement with the power law u(H+) = c(H+)3 observed above the percolation threshold of hydrated nanometric channels. The proton mobility can be described by porosity and tortuosity as phenomenological parameters. Polymer annealing reduces the free volume and porosity of membranes. The proton conductivity can be modulated by changing the hydration number.