The sulfonation of poly(p-phenylenediamine) (P(pPD)) polymer was reported and described in this study. The sulfonated P(pPD) polymers (SP(pPD)) with a degree of sulfonation (S/N molar ratio) range of 0.07 -0.38 were prepared using two different methods; postsulfonation of P(pPD) polymers with fuming sulfuric acid under different reaction conditions and chemical oxidative copolymerization of p-phenylenediamine (pPD) and 2,5-diaminobenzenesulfonic acid (DABSA) monomers with different ratios, using sodium persulfate ((Na)(2)S2O8) as an oxidant. The SP(pPD) polymers obtained were fully characterized and compared by FT-IR, H-1 and C-13 NMR, GPC, WAXD, TGA and SEM. The results obtained showed that the yield, molecular weight, solubility, degree of sulfonation, molecular and morphological structure, and thermal stability of the SP(pPD) polymers are significantly dependent on the polymerization conditions and the sulfonation method. The solubility of SP(pPD) polymers was significantly improved compared to the P(pPD) polymer in most solvents due to the steric effect of the sulfonic groups (-SO3H). On the other hand, the yield, molecular weight and conductivity values obtained for the SP(pPD) polymers were always lower than the values found for P(pPD) polymer, which was attributed to the steric hindrances and the electro-withdrawing effects of the sulfonic groups on the aromatic rings. The TGA results revealed that P(pPD) and SP(pPD) polymers have good thermal stability and decompose above 300 degrees C in nitrogen. (C) 2015 Elsevier Ltd. All rights reserved.