Synthesis and properties of sulfonated poly(ether ether ketone ketone) containing tert-butyl groups as proton exchange membrane materials

A series of sulfonated poly(ether ether ketone ketone)s (SPEEKKs) containing tert-butyl groups were synthesized by aromatic nucleophilic substitution reactions. The polymers with high molecular weights showed good solubility and film-forming capabilities. 1H NMR spectra were used to confirm the DS of polymers. The SPEEKK membranes exhibited good thermal and oxidative stabilities and excellent mechanical properties. The proton conductivities of the SPEEKK-40 and SPEEKK-50 membranes were close to that of Nafion 117 at 80 °C under the same testing conditions. The membranes maintained the original proton conductivities even after a boiling water test for 24 h, indicating the excellent hydrolytic stabilities of the membranes. These results demonstrated that the SPEEKK membranes might have very good prospects in proton exchange membranes fuel cell applications.