Iodination of Sulphonated Poly(ether ether ketone) through N-iodoimide Electrophilic Substitution of Phenoxy Beta-hydrogen

Abstract

Sulphonated poly(ether ether ketone) (SPEEK) demonstrates 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 reaching 71.0% as confirmed by ion chromatography. This work proposes tentative reactivity position and mechanistic hypotheses for a sulphonation of Poly(ether ether ketone) and the subsequent iodination of SPEEK. Effective introduction of iodine is confirmed using 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 Heck reaction), offering a novel strategy for subsequent studies to introduce proton-conductive moieties.