Anhydrous superprotonic polymer by superacid protonation of cross-linked (PNCl₂)_n

We describe a rubbery polymer in which the conductivity reaches values typical of activated Nafion, even though it is completely anhydrous. The protons are introduced into a cross-linked polyphospazene rubber by the superacid HOTf, which is absorbed by partial protonation of the backbone nitrogens. The degree of protonation of the polymer is presumed to be higher than that for the unpolymerized molecular liquid (PNCl₂)₃, where NMR analysis suggests the protonation is about 20%, because the conductivity of the latter is much lower. At a mole fraction of HOTf of x = 0.5 (i.e., H:N = 1), we find that the cross-linked polymer is also much more conductive than the linear polymer with same HOTf mole fraction, implying an increased proton decoupling conduction mechanism. The decoupling of conductivity from segmental relaxation times assessed by comparison with conductivity relaxation times amounts to some 10 orders of magnitude, but with the present measurements, we cannot establish whether it is purely protonic or due equally to a mobile OTf^- or H(OTf)₂^- component.