The synthesis of two random copolymers was carried out by radical copolymerization. Poly(styrene-co-acrylic acid) in a 94:6 (St:AA) molar ratio, partially cross-linked with trimethylol propane trimethacrylate was synthesized by mass polymerization and then sulfonated (PSAAS-m) with sulfuric acid. On the other hand, the same random PSAA was synthesized by solution polymerization, but cross-linked with divinylbenzene and then sulfonated (PSAAS-s). Copolymers, including non sulfonated controls, were dissolved in THF and used to coat a platinum (Pt) electrode by “deep coating” and studied electrochemically by the voltamperometric cycle technique in 0.5 M H2SO4. Both non-sulfonated PSAA copolymers showed only a baseline signal, indicating no proton conductivity through them. The same result was obtained for the PSAAS-s copolymer, suggesting no proton conductivity as well. On the contrary, the copolymer synthesized in mass and highly sulfonated (PSAAS-m) showed the corresponding signals of Pt reduction, similar to the experiment carried out for the Pt electrode without any coating. Ion exchange capacity and water uptake measurements support the electrochemical findings.
