Anion-conducting sulfaminated aromatic polymers by acid functionalization

A simple synthesis technique for the preparation of anionic conducting membranes is presented. In the first step, poly-ether-ether-ketone (PEEK) reacts with chlorosulfonic acid to produce chlorosulfonated PEEK, which in a second step is transformed by reaction with a secondary amine, dimethyl- or diethylamine, into sulfaminated PEEK. The sulfaminated PEEK is cast and the membranes are functionalized in a last step by reaction with various aqueous acid solutions, including HCl, HBr, HNO3, H2SO4, and H3PO4. The spectroscopic, thermal, mechanical, permeability and electrical properties of the membranes are determined and discussed. The combination of appealing properties, such as high elastic modulus (∼1300 MPa), high thermal stability, low cation permeability, respectable anionic conductivity (2-4 mS cm-1), and a relatively simple and inexpensive synthesis make these new ionomers very promising for applications especially in acidic media, like in vanadium redox flow batteries.