Gas Transport Properties of Polynaphthoylenebenzimidazolewith an Ether Bridge Group at Elevated Temperatures

Two-stage original synthesis was used to obtain homogeneous films of polynaphthoylenebenzimidazole with an ester bridge group (PNBI-O): prepolymer (PANI-O) films were first synthesized, and then 100% thermal cyclization at 350 °C was performed to prepare PNBI-O films. The presence of micropores in PNBI-O films is shown by the CO₂ sorption method; the distinct peak is observed at ∼0.55 nm and the vast majority of micropores in PNBI-O are in the range 0.5–0.65 nm. It was established by the DMA method that the glass transition of PNBI-O takes place at 450 °C. A differential gas chromatographic method was utilized to measure gas permeability coefficients (<i>P</i>) of six gases (He, H₂, CO₂, CH₄, O₂, and N₂) at 150–250 °C. Temperature coefficients (the apparent activation energies) of permeability were determined. <i>P</i>(H₂) = 162 Barrer and ideal selectivity (α) = 16 for H₂/CO₂ were attained. These values are higher than the 2008 Robeson upper bound. The analysis of permeability of the components of H₂–CO₂ gas mixtures of various compositions at 250 °C showed that the H₂/CO₂ separation factor can be higher by 3.5 times than ideal selectivity. Thus, the capabilities of PNBI-O as the polymer for high-temperature separation membranes for the separation of industrial hydrogen-containing mixtures were demonstrated.