Phosphonated Polymers with Fine-Tuned Ion Clustering Behavior: Toward Efficient Proton Conductors

Abstract

We report the controlled synthesis, self-assembly, and ion transport properties of polystyrene bisphosphonate (PSbP) and polystyrene phosphonate (PSP) based polymers, revealing that ion clustering in PSbP (characterized by precisely determined phosphonate group location) was markedly suppressed compared to that in PSP despite the 2-fold higher phosphonic acid group concentration in the former. Moreover, confinement of PSbP chains to ordered nanoscale domains in PSbP-based block copolymers offered a platform for creating nearly homogeneous ionic phases with a radically decreased potential barrier to ion conduction. Notably, the decrease in the degree of polymerization of PSbP chain in the block copolymers by half (i.e., the lower acid group contents) led to 2-3 times improved anhydrous conductivity with incorporated ionic liquids, contrary to the results commonly reported for a range of acid-tethered polymers. Our work provides a first-time demonstration of well-defined self-assembled morphologies of bisphosphonate block copolymers, opening a new chapter in the development of highly conductive phosphonated polymers and thus being of importance to the field of polymer electrolytes.