Influence of the polymer backbone structure on the properties of aromatic ionomers with pendant sulfobenzoyl side chains for use as proton-exchange membranes.
Six different ionomers having various aromatic polymer backbones with pendant 2-sulfobenzoyl side chains were prepared by nucleophilic aromatic substitution reactions of lithium 2,6-difluoro-2'-sulfobenzophenone with 4,4-biphenol, 2,7-dihydroxynaphthalene, 4,4-isopropylidenediphenol, 4,4-dihydroxydiphenyl ether, 4,4'-thiodiphenol, and 4,4'-thiobisbenzenethiol, respectively, to produce four poly(arylene ether)s, one poly(arylene ether sulfide), and one poly(arylene sulfide). Mechanically tough proton-exchange membranes with ion-exchange capacities in the narrow range from 1.9 to 2.3 mequiv/g were cast from the high-molecular-weight ionomers, and subsequently investigated with respect to their structure-property relationships. Glass transitions were only detected for ionomers in the sodium salt form, and increasing glass-transition temperatures (Tg) were found to give higher thermal decomposition temperatures. Analysis by small-angle X-ray scattering indicated that the ionic clustering was promoted for ionomers with flexible polymer backbones and low Tg values. The proton conductivity of the membranes at 80 °C under fully humidified conditions was found between 0.02 and 0.2 S/cm and appeared to depend primarily on the Tg.
Polymer & Materials Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden.
Elin Persson
EP
Jutemar
Patric
P
Jannasch
D003460:Crystallization / Q000379:methods*; D006841:Hydrocarbons, Aromatic / Q000737:chemistry*; D008422:Materials Testing; D008567:Membranes, Artificial; D036103:Nanotechnology / Q000379:methods*; D011522:Protons
D006841:Hydrocarbons, Aromatic; D008567:Membranes, Artificial; D011522:Protons