Electrochemical synthesis of ion exchange polymers: Comparison between hydroxide and proton conductors

We report the electrochemical synthesis of proton- and hydroxide-conducting ionomers. Sulfonated poly(phenyl ether) with various degree of functionalization was synthesized starting from a precursor isomer mixture or from pure ortho- or para-hydroxybenzenesulfonic acid. The ionic conductivity can be related to the different ion exchange capacity of the ionomers. Two hydroxide-conducting ionomers were prepared from (N-allyl-N-benzyl-N,N-dimethyl)ammonium iodide (ABDMA) or N-(p-vinylbenzyl)-N, N,N-trimethylammonium chloride (VBTMA). The ionic conductivity of VBTMA polymer is two orders of magnitude higher than that of ABDMA. This result can be explained by the different structure of the two polymers, which changes the ion mobility drastically. The electrochemical synthesis of ionomers is a promising research field, where many advances can be made by clever choice of highly functionalized precursor monomers with appropriate positions of the ionic groups.