New Hydrocarbon Proton Exchange Membranes Based on Sulfonated Styrene-Ethylene/Butylene-Styrene Triblock Copolymers

Abstract

Commercially available styrene-ethylene/butylene-styrene triblock polymer (Kraton G 1650) was partially sulfonated using a SO₃/triethyl phosphate reagent in a dichloroethane/cyclohexane mixed solvent. Films of the product were cast from lower alcohols to give elastic materials with different degrees of sulfonation (ca. 30–60%) as determined by titration. Transmission electron microscopy suggests that the cast films possess cylindrical sulfonated polystyrene domains. The films swell in water, with the extent of swelling being dependent on the sulfonation level. Ionic conductivities as high as 8.5 × 10⁻² S/cm are obtained when fully hydrated, and compare favorably to those exhibited by hydrated, sulfonated fluoropolymers such as Nafion.