Iodination of sulphonated poly(ether ether ketone) through N-iodoimide electrophilic substitution of phenoxy beta-hydrogen

Sulphonated poly(ether ether ketone) (SPEEK) exhibits excellent mechanical properties as a proton exchange membrane. However, its proton conductivity remains insufficient for practical applications. To address this limitation, a covalent incorporation of proton-conductive functional groups into the SPEEK matrix is proposed to establish continuous proton transport channels. Herein, through an iodination reaction of N-iodosuccinimide with SPEEK, we have successfully synthesised iodinated sulphonated poly(ether ether ketone) (I-SPEEK) with an iodination efficiency of 71.0% as confirmed by ion chromatography. This work proposes tentative reactivity positions and mechanistic hypotheses for the sulphonation of poly(ether ether ketone) and the subsequent iodination of SPEEK. Effective introduction of iodine is confirmed by Fourier-transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies. Meanwhile, I-SPEEK serves as a precursor that provides grafting sites for hydrophilic groups (e.g. vinyl-silanes via the Heck reaction), offering a novel strategy for subsequent studies to introduce proton-conductive moieties.