Influence of the Polymer Backbone Structure on the Properties of Aromatic Ionomers with Pendant Sulfobenzoyl Side Chains for Use As Proton-Exchange Membranes

摘要

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-dihydroxynaph-thalene. 4.4-isopropylidenediphenol, 4,4-dihydroxydiphenyl ether, 4.4'-thiodiphenol, and 4,4'-thiobisbenzenethiol. respectively, to produce four polytarylene etherls. one polylarylene 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-ttansition temperatures (T_g) 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 T_g 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 T_g.