Effect of sulfonating agent in the properties of styrene copolymers for PEMFC membranes

Two different sulfonating agents: sulfuric acid (S) and acetyl sulfate (AcS) were evaluated for chemical modification of poly (styrene-co-butyl acrylate) (StBuA) copolymer, as low-cost membranes. The reaction was carried out by direct sulfonation during 2–5 h of sulfonation time. FTIR confirmed sulfonation through the presence and widening of the several SO3H characteristic absorption bands. The molecular weight decreased after sulfonation, compared with pristine StBuA. TGA thermal analysis showed stability over 150 ᵒC with residues suggesting crosslinking and a glass transition (Tg) enhanced. Even with higher Tg values, sulfonated copolymers became flexible, as seen by their lower complex modulus (E∗). Ion exchange capacity (IEC) ranged from 0.91 to 1.53 meq g−1 and degree of sulfonation (DS) from 7 to 40%. The proton conductivity for sulfonated membranes exhibited similar or higher to Nafion membrane, particularly for S-4h membranes. A Grotthuss mechanism is envisaged for AcS and vehicular mechanism for S membranes.