New comb-shaped ionomers based on hydrophobic poly(aryl ether ketone) backbone bearing hydrophilic high concentration sulfonated micro-cluster

Abstract

A new difluoride monomer containing an aliphatic bridge between 2,6-difluoropheyl and hexaphenylbenzene is designed and synthesized. Then, a series of novel hexa-sulfonated poly(aryl ether ketone)s (HS-PAEK-x) containing an aliphatic spacer between hydrophobic poly(aryl ether ketone)s main chain and hydrophilic sulfonated hexaphenylbenzene are prepared from the new difluoride monomer with 4,4′-(hexafluoroisopropylidene) diphenol and 4,4′-difluorobenzophenone by nucleophilic polycondensation, and subsequent postsulfonation using chlorosulfonic acid. All the polymers give tough, flexible, and transparent membranes by solvent casting. The membranes with comparatively low ion exchange capacity (IEC) values ranging from 0.87 to 1.42 meq g−1, achieve good mechanical properties, suitable proton conductivity (111 mS cm−1) compared with Nafion 117 at 80 °C, and excellent dimensional stability (the highest swelling ratio of length is 9.2% at 80 °C). Furthermore, compared with the previous reported polymers with similar main chain, such as the polymer with pendant sulfoalkyl groups and hollow aromatic hexa-sulfonated polymer, the HS-PAEK-x exhibit higher proton conductivities at similar IEC level, which attributes to the specific molecular structure and improving morphology. Overall, all of the above-mentioned results indicate that the HS-PAEK-x membranes are good candidate materials for proton exchange membranes (PEMs).