Polynaphthoylenebenzimidazoles for gas separation – Unexpected PIM relatives

Semi-ladder high-molecular polynaphthoylenebenzimidazoles (PNBI) were synthesized through polyaminonaphtoyleneimide (PANI) formation and thermal cyclization at 350 °C. The structures of PANIs and PNBIs were confirmed by NMR, GPC and FTIR. Polymer films were obtained from PANI pre-polymer by solution-cast technique. After thermal cyclization, the PNBI films exhibit excellent mechanical properties: tensile strength of 95–174 MPa, Young's modulus of 1.5–2.4 GPa and elongation at break of 10–50%. The PNBIs are located near the upper bound of the 1991 Robeson diagram for O 2 /N 2 , H 2 /N 2 and H 2 /CH 4 gas pairs, while the PNBI with a hexafluoroisopropylidene bridge (PNBI-4) overcomes it for CO 2 /CH 4 , approaching the upper bound of the 2008 Robeson diagram. A peculiarity of the synthesized polymers is lower gas diffusion coefficients and higher gas solubility coefficients, which are close to polypyrrolones and PIM family polymers. The higher PNBI diffusion selectivity identifies them as organic molecular sieves, as confirmed by the specific surface area of PNBI-4, which is close to PIM-1. The data obtained allows to classify the studied PNBIs as unexpected PIM relatives. The synthesized PNBIs are polymer molecular sieves and, unexpectedly, belong to the polymer of intrinsic microporosity family. • The PNBI gas transport properties have been obtained. • The studied PNBIs lie on the upper bounds of the 1991 Robeson diagrams. • PNBI-4 is higher than the upper bound on the 1991 Robeson diagram for CO 2 /CH 4 . • PNBI-4 is approaching the upper bound of the 2008 Robeson diagram for CO 2 /CH 4 . • PNBI-4 possesses a microporous structure similar to the one of PIM-1.