Preparation and evaluation of a proton exchange membrane based on crosslinkable sulfonated poly(ether ether ketone)s

A series of crosslinkable sulfonated poly(ether ether ketone)s (SPEEKs) containing propenyl groups were synthesized by aromatic nucleophilic substitution reactions. 1H NMR spectra were used to confirm the DS of polymers. The resulting polymers showed high molecular weights and good solubility and could be cast into tough membranes. The SPEEK membranes in acid form possessed good thermal stabilities and mechanical properties. The methanol diffusion coefficients ranged from 9.70 × 10−8 to 4.18 × 10−7 cm2 s−1, which were much lower than that of Nafion 117® (2.38 × 10−6 cm2 s−1). The proton conductivity of the SPEEK-3 membranes (0.072 S cm−1) was close to that of Nafion 117® (0.083 S cm−1) at 85 °C under the same testing conditions. These results showed that the synthesized materials might have potential applications as the proton exchange membranes for PEMFCs.