Aromatic Poly(ether ketone)s with Pendant Sulfonic Acid Phenyl Groups Prepared by a Mild Sulfonation Method for Proton Exchange Membranes

The sulfonation selectivity of seven poly(ether ether ketone)s (PEEKs) was investigated, and several possessed targeted single-or double-substituted sites per repeated unit on pendant phenyl groups via the postsulfonation approach.The presence of the various pendant groups enabled postsulfonation to occur under mild reaction conditions, in much shorter times than required for the sulfonation of commercial PEEK.A series of poly(ether ketone)s (PEKs) with ion exchange capacity of 2.23-0.84mequiv/g could be realized by controlling the length of unsulfonated segments of both homopolymers and copolymers.These side-group sulfonation polymers had excellent mechanical properties, good thermal and oxidative stability, and good dimensional stability in hot water.The methanol permeability values of Me-SPEEKK, Me-SPEEKDK, Ph-SPEEKK, and Ph-SPEEKDK at room temperature were in the range 3.31 × 10 -7 -9.55 × 10 -8 cm 2 /s, which is several times lower than that of Nafion 117.Me-SPEEKK and Ph-SPEEKK also exhibited high proton conductivity of 0.15 S/cm at 100 °C, which is higher than that of Nafion 117.Transmission electron microscopy analysis was used to observe their microstructure for evidence of microphase separation of ionic and hydrophobic domains.The results showed these side-group-acid materials are possible inexpensive candidate materials for proton exchange membranes in fuel cell applications.