Soft block sulfonated styrene–butadiene–styrene (SBS) triblock copolymer proton exchange membranes

Abstract

A new synthetic method that generates a middle block sulfonated SEBS proton exchange membrane through partial hydrogenation of polystyrene-b-polybutadiene-b-polystyrene and a subsequent thiol–ene click reaction and oxidation. By switching the sulfonation site from hard polystyrene end blocks to the soft poly(ethylene-r-butylene) middle block, the middle block sulfonated SEBS membranes showed lower swelling in water and greater dimensional stability than conventional polystyrene block sulfonated SEBSs with similar sulfonate concentrations because of the lack of the plasticization effect of the polystyrene block. Water uptake can be suppressed further by crosslinking unreacted carbon–carbon double bonds in the backbone after the thiol–ene click reaction by the addition of a photoacid. Crosslinked membranes showed good conductivity in water and resilient mechanical properties in stress–strain analysis.