Synthesis and properties of sulfonated block poly(arylene ether)s containing m-terphenyl groups as proton conductive membranes

Abstract

We have utilized m-terphenyl (MTP) moiety as a component of hydrophobic blocks for sulfonated multiblock poly(arylene ether) copolymers. For this purpose, bisphenol-type MTP monomer was polymerized with bis(4-fluorophenyl)sulfone to obtain hydroxyl-terminated hydrophobic oligomers, which were copolymerized with sulfonated hydrophilic blocks to obtain the targeted multiblock copolymers. The block copolymers possessed high apparent molecular weight (Mw=74–180kDa) and gave bendable membranes by solution casting. Transmission electron microscopic (TEM) images revealed that the membranes exhibited hydrophilic/hydrophobic phase-separated morphology with distinct interfaces. The domain sizes were dependent on the compositions of the multiblock copolymers, indicating the sequenced structure is responsible for the morphology. The introduction of MTP moieties in the hydrophobic blocks resulted in the membrane with the higher ion exchange capacity (IEC) value (2.13meq/g) and higher proton conductivity (ca. 320mS/cm at 80°C and 90% relative humidity) than that of the previous polymers sharing the same hydrophilic but different hydrophobic (p-biphenyl, BP) moieties (1.69meq/g, ca. 200mS/cm under the same conditions, respectively). In contrast, humidity dependence of dynamic mechanical properties in MTP membranes was similar to BP membranes, suggesting the introduction of MTP moieties in the hydrophobic segments has minor impact on the mechanical stability and its dependence on the humidity.