The molecular features governing the transfer of protons in recently synthesized membranes prepared from polymeric organic amine salts are investigated with first principles based electronic structure calculations. Global minimum energy structures were determined for bisulfates and dihydrogenphosphates of monomeric fragments of 2-vinylpyridine, 4-vinylpyridine, and vinylimidazoline. The equilibrium structures fully optimized at the B3LYP/6-311G** level indicate that the energetically preferred state for the phosphates is consistently as a phosphoric acid/base pair in contrast to the bisulfates of 2-vinylpyridine and vinylimidazoline where a proton is transferred to the base resulting in the protonated base/bisulfate contact ion pair. Binding energies of the acid/base or anion/protonated base pairs were computed from equilibrium structures fully optimized with the counterpoise method to correct for basis set superposition error and show that the transfer of the proton results in substantially stronger binding. The energetics for the transfer of the proton from the acid to the amine base and revealed that if the transfer is constrained (i.e. the O–H…N hydrogen bond) a barrier of as much 2.5 kcal/mol occurs. However, if the transfer is performed without imposing any constrains on either molecule the barrier disappears. Proton transfer with phosphoric acid showed endothermic penalties of 6.0, 5.0 and 2.2 kcal/mol for 4-vinylpyridine, 2-vinylpyridine, and vinylimidazoline, respectively. This was in contrast to sulphuric acid where the penalties were exothermic by 0.8 and 4.4 kcal/mol for 2-vinylpyridine and vinylimidazoline, but only very slightly endothermic with 4-vinylpyridine. These energetics are generally consistent with the low temperature conductivities of solution-cast polymeric amine salts determined from impedance measurements. Furthermore, these results imply that the measured high temperature (i.e. > 120 °C) conductivities are not simply due to the hopping of protons but involve the mobility of the larger protonic charge carriers (i.e. phosphoric acid).

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