Sulfonated copoly(arylene ether nitriles) as proton exchange membrane with excellent mechanical and thermal properties

Abstract

A series of sulfonated biphenol poly(arylene ether nitriles) (BP-SPEN) copolymers were synthesized by the nucleophilic aromatic substitution polymerization of 2,6-difluorobenzonitrile with different ratios of hydroquinonesulfonic acid potassium salt and biphenol in the presence of potassium carbonate. The composition and structures of the BP-SPEN copolymers were characterized by Fourier transform infrared spectroscopy. Thermal properties, mechanical properties, proton conductivity, and water uptake of copolymer membranes were also investigated. The results showed that they present high glass transition temperature ranging from 131°C to 180°C and good thermal stability with the 5% weight loss temperatures in the range of 284–287°C under nitrogen atmosphere. They also exhibited good mechanical property with the tensile strength in the range of 68–109 MPa in the dry state and 31–72 MPa in the wet state. Furthermore, these copolymer membranes exhibited good water uptake ranging from 8.8% to 39.9%. Thus, the membranes had good proton conductivities in the range of 1.09 × 10⁻⁵–1.54 × 10⁻³ S cm⁻¹ at room temperature and 100% relative humidity. The influence of temperature on water uptakes, tensile strength, and proton conductivity was also investigated.