Protic Poly(Diallylammonium Sulfonate)s: Toward Water-Processable Fluorine-Free Ionic Materials

In this work, we report the synthesis of a new family of fluorine-free protic poly(ionic liquid)s via free-radical cyclopolymerization of protic diallylammonium monomers. Protic ionic liquid monomers based on diallylmethylammonium (DAMAH⁺) and diallylammonium (DAAH₂ ⁺), combined with different alkyl sulfonate counter-anions, were first prepared. Cyclopolymerization yielded a systematic series of six poly(diallylammonium) cations, five of which are newly reported here, combining two polymer backbones-poly(DAMAH⁺) and the newly incorporated poly(DAAH₂ ⁺)-with three fluorine-free sulfonate anions, namely mesylate (MsO^-), ethylsulfonate (EsO^-), and dodecylbenzenesulfonate (DBsO^-); the previously reported poly(DAMAH⁺MsO^-) analogue was included for direct comparison within the same series. Systematic characterization reveals how the interplay between polymer backbone and counter-anion governs solubility in water and organic solvents, glass transition temperatures (20-55°C), thermal stability (up to 300°C), and ionic conductivity (up to 10^-3 S cm^-1 at 100°C). The combination of their physicochemical properties, electrochemical stability, and water processability highlights these polymers as a versatile fluorine-free platform for electrochemical technologies. To demonstrate this potential, selected polymers were evaluated as water-processable binders for LiFePO₄ cathodes, where they delivered competitive rate capability and stable electrode performance compared to PVDF. Their protic ionic character further suggests opportunities for future applications toward proton-conducting materials. Overall, this work introduces a sustainable platform for the development of fluorine-free ionic polymers with broad potential for electrochemical technologies.