Ion and Chain Mobility in a Tetrazole Proton-Conducting Polymer

The morphology, relaxation properties, and conductivity of the statistical copolymer polystyrenic (alkoxy 1<i>H</i>-tetrazole-<i>co</i>-alkoxy nitrile), an anhydrous proton conductor, were measured. The material phase-separates into hard and soft domains, the latter corresponding to a phase richer in the pendant tetrazole groups. Using dielectric and mechanical spectroscopies, two relaxation processes were observed, the slower associated with local segmental dynamics of the backbone and the higher-frequency process involving motion of the tetrazole moieties. The latter is coupled to the ionic conductivity, which means that below the principal glass transition of the material (∼313 K) the conductive mechanism remains active. Thus, the usual compromise in proton exchange membranes between mechanical stability and ion conductivity can be avoided.