Synthesis and properties of highly branched star-shaped sulfonated block polymers with sulfoalkyl pendant groups for use as proton exchange membranes

• Two types of star-shaped block polymers.
• Polymers containing sulfoalkyl pendant groups.
• Exhibit considerable conductivity and oxidative stability.

Branched sulfonated copoly(ether ketone)s exhibit excellent properties for use as proton exchange membranes (PEMs). However, to date, the use of highly branched star-shaped sulfonated block polymers with flexible side chains as PEMs has not been reported. In this study, two novel types of star-shaped block poly(arylene ether sulfone)s containing sulfoalkyl pendant groups with 6% branching agent were synthesized for the first time. The properties of the polymer with hydrophilic segments surrounded by hydrophobic segments (SPAES-6s) and of the polymer with hydrophobic segments surrounded by hydrophilic segments (SPAES-6f) were investigated, with a focus on their potential use as PEMs. The block polymers SPAES-6f and SPAES-6s exhibited higher proton conductivities (0.42 S cm−1 and 0.30 S cm−1 at 80 °C) than those of the random polymer SPAES-6r and Nafion 117, and SPAES-6s exhibited better oxidative stability (435 min) and dimensional stability than SPAES-6f. The results indicate that the highly branched sulfonated block poly(arylene ether sulfone)s with sulfoalkyl pendant groups are good candidate PEM materials for fuel cell applications.