Different PPO-SH ionomers were obtained by sulfortation of poly(2,6 -dim ethyl- 1,4-phenyleneox i de) (PPO). The sulforiation was assessed by FTIR and XPS spectroscopies. The acid form of the ionomers was characterized by means of H-1 and C-13 MAS-NMR spectroscopies. Then, polymers were hydrated under controlled humidity atmosphere and NMR and electrical conductivity studies performed. In the hydrated samples, two stages associated with formation of hydronium (H3O+) species and proton hopping between adsorbed water molecules have been deduced. Both processes participate in the conductivity of PPO-SH samples. (c) 2007 Elsevier B.V. All rights reserved.