para fluoro-thiol clicked diblock-copolymer self-assembly: Towards a new paradigm for highly proton-conductive membranes

Sulfonated sPPFS-b-PBuA diblock and statistical copolymers based on 2,3,4,5,6-pentafluorostyrene PFS and butyl acrylate BuA were elaborated for Proton Exchange Membrane Water Electrolyser (PEMWE) purposes. The block copolymers (BCP) were synthetized by Nitroxide Mediated Polymerization NMP, a controlled radical polymerization technique that yields a well-defined molar mass and a low dispersity material. These diblock-copolymers have the ability to self-assemble due to the immiscibility of the two macromolecular segments PPFS and PBuA. Statistical copolymers of the similar chemical composition were synthetized by both controlled radical polymerization NMP in solution and by free radical polymerization FRP in emulsion as waterborne dispersed polymer with highest molar mass. The copolymers were sulfonated by a mild click-reaction, namely an organo-catalyzed nucleophilic substitution reaction with sodium 3-mercapto-1-propanesulfonate (SMPS) at low temperature. The morphology of the sulfonated diblock-copolymer BCP was studied by SAXS and AFM, revealing a nano-phase-segregated sulfonated membrane. The mechanical properties of the membranes were improved by ionic crosslinking with polybenzimidazole (PBI-OO). Finally, the conductive properties of the sulfonated BCPs and statistical copolymers were investigated as a function of parameters such as the morphology of the BCP, the molar mass, and the sulfonation degree of the materials.