One-pot synthesis of high molecular weight sulfonated poly(oxadiazole-triazole) copolymers for proton conductive membranes

For the first time, a series of high molecular weight (1-4 × 10⁵ g mol^-1) sulfonated poly(oxadiazole-triazole) copolymers have been synthesized at high temperatures and very short reaction time, by a single-step method based on solution polycondensation reaction of non-sulfonated dicarboxylic acid, hydrazine sulphate and aromatic primary amine (sulfonated and non-sulfonated) in poly(phosphoric acid). By this fast synthetic procedure, copolymers with a high conversion to triazole groups (up to 93%) as well high sulfonation level (IEC = 1.17-1.84 mequiv. g^-1) have been obtained. The structure of the polymers was characterized by elemental analysis and ¹H NMR. Since high sulfonation levels (IEC = 1.17-1.84 mequiv. g^-1) could be obtained, membranes were prepared from these polymers and have been characterized aiming the application in fuel cells. Proton conductivity up to 6 × 10^-2 S cm^-1 at 150 °C was measured. The polymer films had good mechanical properties with storage modulus of about 3 GPa at 300 °C. These films exhibited high thermal stability with T_g up to around 440 °C.