Preparation, characterization, and properties of poly(styrene-b-sulfonated isoprene)s membranes for proton exchange membrane fuel cells (PEMFCs)

• Poly(styrene-b-sulfonated isoprene) membranes were prepared.
• The membranes produce proton conductivity values up to 10−1 S/cm above 60 °C.
• The membranes benefit from 50% lower methanol permeability than that of Nafion-117.
• As the hydrophilic block length is increased, the proton conductivity also increased.

A series of poly(styrene-b-isoprene) block copolymers (PSI) were synthesized by sequential anionic polymerization of styrene and isoprene. Poly(styrene-b-sulfonated isoprene) block copolymers (PSsI) were prepared via reacting the double bonds of the isoprene block with 1,4-dioxane/sulfur trioxide. The spherical-shaped ionic clusters within the PSsI membranes produce a comparable proton conductivity (10−1 S/cm above 60 °C) but benefits from approximately 50% lower methanol permeability than that of Nafion-117. Properties, such as proton conductivity and water content values, of PSsI membranes correlate highly to the content of the sulfonated isoprene block in PSsI samples even in the cases of similar IEC. As the hydrophilic block length is increased, the water content and proton conductivity also increased.

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