Poly(aryl ether ketone) containing flexible tetra-sulfonated side chains as proton exchange membranes

Polymer Chemistry Pub Date: 2013-11-01 DOI: 10.1039/C3PY01350B

Abstract

A new difluoride monomer containing electron-rich tetraphenylmethane was designed and synthesized. Based on this monomer along with 4,4′-(hexafluoroisopropylidene)diphenol (6FBPA) and 4,4′-difluorobenzophenone (DFB), a series of tetra-sulfonated poly(aryl ether ketone)s (TS-PAEK-x) were prepared by nucleophilic polycondensation, followed by a sulfonation reaction using chlorosulfonic acid. Tough, flexible, and transparent membranes were obtained by solvent casing. These membranes with ion exchange capacity (IEC) values ranging from 0.85 to 1.43 meq. g?1 exhibited good mechanical properties, excellent dimensional stability, and suitable proton conductivity. The largest swelling ratio (in-plane direction) with a value of 10.3% was observed from TS-PAEK-25 (IEC = 1.43 meq. g?1) membranes at 100 °C, which was much lower than that of Nafion 117 under the same conditions. The highest proton conductivity of 151 mS cm?1 was obtained from the TS-PAEK-25 membrane at 100 °C in the fully hydrated state. Compared to Nafion 117, TS-PAEK-25 with comparable water content exhibited a superior effective proton mobility (μ) value (up to 1.19 × 10?3 cm2 s?1 V?1). Under reduced humidity conditions, TS-PAEK-25 showed desired conductivity considering its lower IEC level. The results indicate that the TS-PAEK-x membranes are promising candidates for application as proton exchange membranes.

Graphical abstract: Poly(aryl ether ketone) containing flexible tetra-sulfonated side chains as proton exchange membranes
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