Synthesis and properties of highly branched star-shaped sulfonated block poly(arylene ether)s as proton exchange membranes

Star-shaped sulfonated block copoly(ether ketone)s exhibit excellent properties for use as proton exchange membranes (PEMs). However, very few investigations of the use of highly branched star-shaped sulfonated block polymers as PEMs have been reported. In this work, two types of highly branched star-shaped sulfonated block poly(arylene ether)s with 6% branching agent were synthesized via direct polycondensation reactions of a trifunctional core (branching agent) with sulfonated 4,4′-difluorobenzophenone, bisphenol fluorene, and 4,4′-difluorodiphenyl sulfone. The properties of a polymer with hydrophilic segments surrounded by hydrophobic segments (P1) and a polymer with hydrophobic segments surrounded by hydrophilic segments (P2) were investigated. The block polymer P1 exhibited better oxidative stability (332 min) and dimensional stability (<12%) than the highly branched sulfonated random polymer (P3), whereas P2 exhibited higher proton conductivity (0.40 S cm−1 at 80 °C) and water uptake (59.1% at 80 °C) than P3. The highly branched star-shaped sulfonated block poly(arylene ether)s exhibit greater potential than P3 for use as PEMs.