Series of sequenced sulfonated naphthalenic polyimides with improved solubility were prepared by polycondensation in m-cresol using aromatic diamines containing phenylether bonds and/or bulky groups. Sulfonated polyimides were characterized by NMR and IR spectroscopies. Membranes were prepared by solution casting method and characterized by determining the ion-exchange capacity, water swelling, proton conductivity whereas the morphology of polymer membranes was studied by small angle neutron scattering.