Abstract: Polybenzimidazoles (PBIs) containing ether bonds were synthesized via a facile method using 3, 3'-diaminobenzidine and 4, 4'-dicarboxydiphenyl ether as monomers and phosphorus pentoxide/methanesulfonic acid solution as solvent. PBIs with different molecular weights can be obtained by changing the reaction temperature and time. Fourier transform infrared (FT-IR) spectrometer and hydrogen nuclear magnetic resonance (¹H-NMR) were used to confirm the structure of polybenzimidazole with ether bonds, and gel permeation chromatography (GPC) was applied to measure the molecular weight of polybenzimidazole. The effects of molecular weight on the solubility of PBI as well as the mechanical properties of PBI membrane were then investigated to determine the optimum synthetic condition for PBI. The results show that when the reaction time is 2 h and the reaction temperature is 140℃, the weight-average molecular weight of the resultant PBI can reach 4.9×10⁵. The PBI shows excellent mechanical properties and good solubility in common polar solvent without addition of lithium chloride. The tensile strength, elongation at break, and tensile modulus of PBI obtained at the optimal condition are 100.8 MPa, 11.4%, and 1 609 MPa, respectively. The thermal stability of the resultant PBI was then characterized by thermogravimetic analysis, and the influence of the immersing time on the phosphoric acid (PA) doping level and the effect of temperature on the proton conductivity of PBI were investigated as well. The results show that the temperature of initial decomposition of PBI obtained at 140℃ for 2 h reaction is as high as 530℃, indicating a very outstanding thermal stability. In addition, the prepared PBI can absorb 222% of PA when it is immersed in 85% PA solution at 80℃ for 2 d. The PA-doped PBI membrane shows a proton conductivity of 16.3 mS/cm at 170℃ and a conduction activation energy of 21.0 kJ/mol under anhydrous condition, thus making it highly suitable for applications as high temperature proton exchange membrane.