Synthesis of sulfonated polybenzimidazoles from functionalized monomers: Preparation of ionic conducting membranes

In the present work, a new sulfonated tetraamine and the corresponding sulfonated polybenzimidazoles (sPBI) were synthesized. For the sake of determining the best polymerization conditions, a study involving model compounds was first performed. A strong acid medium was used as polymerization solvent, which allowed to obtain high molecular weight sPBI. A series of polymers with ion exchange capacity (IEC) ranging from 0 to 2.6 mequiv/g were synthesized using a non-sulfonated tetraamine as a comonomer. The chemical structure of those polymers was confirmed by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) as well as by titration. Thermogravimetric analysis (TGA) and viscosity measurement were performed as well. On the other hand, different architectures of the copolymers were prepared, i.e., random, sequenced copolymers, and blends of the homopolymers. The membranes prepared from the sPBI display low water uptake. The ionic conductivities measured in the hydrated state at room temperature ranged from 10(-6) to 4 x 10(-4) S cm(-1).