In situ polymerization: A novel route for thermally stable proton-conductive membranes

In this paper, a new solvent-free route for preparing proton-conductive membranes is proposed. Flexible and fiber-supported polymer electrolyte membranes, as potential proton exchange membranes, were readily obtained by in situ polymerization of a homogenous solution that consisted of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO, polymer)–monomer mixtures of styrene (ST) and divinylbenzene (DVB), which was pre-cast onto SEFAR PETEX fibers. Factors such as the components of the casting solution and the sulfonation time, were fully investigated. The membrane structure and components were confirmed by FTIR-ATR spectra and SEM-EDXA images, and the thermal stability was examined via TGA and DrTGA. The membrane exhibited a proton conductivity of about 0.07 S/cm at 100% humidity and at room temperature, which is close to that of Nafion 117 at identical conditions (around 0.08 S/cm), whereas its thickness (about 120 μm) was less than that of Nafion 117. The tensile strength and the elongation at the break of the membrane were 31.2 MPa and 71%, respectively, which are several times higher than those of Nafion (about 6.16 MPa tensile strength and 36% elongation ratio). The dimensional change ratio of the membrane between the wet and dry states was below 3%, which is much lower than that of Nafion 117. The membrane showed a high thermal stability up to 400 °C. The method can be applied to other compatible systems of (aromatic) polymers and (aromatic) monomers.