Siloxane Crosslinked Imidazolium PPO/PTFE Membranes for High Temperature Proton Exchange Membranes

Based on poly (2,6-dimethyl-1, 4-phenylene oxide) (PPO) , novel high temperature proton exchange membranes were prepared with high phosphoric acid content, superior proton conductivity and excellent mechanical properties. Both methylimidazole (MeIm) and triethoxysilylpropyldihydroimidazole (SiIm) were used as functional reagents to graft the imidazolium groups onto the PPO polymer, in which the imidazolium group provided the phosphoric acid interaction sites. Meanwhile crosslinking of the modified PPO was achieved by forming a crosslinked silane network via the hydrolysis reaction of SiIm in an acidmedium. Moreover, porous poly (tetrafluoroethylene) (PTFE) was used as the membrane matrix toenhance the dimensional stabilities and mechanical strength of the fabricated membranes. Physicochemical properties of composite membranes with various crosslinking degrees were investigated accordingly. The results showed that the PPO-SiIm-MeIm/PTFE composite membranes possessed dense structure, superior thermal stability, improved chemical stability, high conductivity and suitable mechanical strength simultaneously. As an example , the PPO-50% SiIm-50% MeIm/PTFE membrane with a phosphoric acid doping content of 242. 5% exhibited a conductivity of 0. 09 S/cm at 160 degrees C under no humidification conditions, and a tensile strength of 3. 6 MPa at room temperature. The results indicate that PPO-x% SiIm-y% MeIm/PTFE membranes have the potential to be used as HT-PEMs.