Ion clustering behavior of “precise” phosphonated polymers

Polymers functionalized with phosphonic acid groups are promising candidates of proton exchange membranes for fuel cells that can be operating at high temperatures. This is owing to the amphoteric nature and self-dissociation ability of phosphonic acid groups, unlike sulfonic acid counterparts, thereby allowing acid groups to form hydrogen-bond networks in the absence of moisture. In the present study, we report the synthesis of polymers bearing phosphonic acid groups at the precise position. For this purpose, controlled radical polymerization of styrene phosphonate was carried out, where the substitution positions were varied based on ortho, metal, para directing groups. It has been revealed that polymers tethered with phosphonic acid groups at meta and ortho positions display suppressed ion clustering behavior than those with para position acid group, attributed to the dominant hydrogen bonding interactions of neighboring acid groups.