The cross-link reaction between macromolecular chains of sulfonated poly(ether ether ketone) (SPEEK) by thermal treatment above 150 degrees C in presence of dimethylsulfoxide (DMSO) is investigated by various techniques, including elemental analysis, acid-base titration, infrared spectroscopy, water uptake (WU) measurements, and thermogravimetry. The conditions of thermal treatment are analyzed. The cross-linking reaction occurs in at least three more or less activated and deactivated positions with different activation energies, leading to different time dependencies of the cross-link reaction. The role of residual solvent DMSO is studied particularly: the cross-linking depends significantly on the amount of solvent in the membranes. Implications on WU and thermal stability are of particular importance for the development of high performance proton-conducting membranes

The thermal and mechanical behavior, the water uptake (WU), and water diffusion coefficient of sulfonated poly(ether ether ketone) (SPEEK)membranes annealed at 180 degrees C for different times were explored by high-resolution thermogravimetric analysis, mechanical tensile tests, dynamic mechanical analysis, and WU measurements. The mechanical and thermal stability increased with the thermal treatment time, i.e., with the degree of crosslinking. The effect of residual casting solvent, dimethyl sulfoxide (DMSO), on the WU within SPEEK was probed. In presence of residual DMSO, crosslinked SPEEK exhibited higher water sorption at low and medium relative humidity (RH), and lower water sorption at high RH. These membranes have properties well adapted to fuel cell applications

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