Synthesis and Gas Transport Properties of Polynaphthoylenebenzimidazoles with Keto- and Sulfonic Bridging Groups

Polynaphthoylenebenzimidazoles (PNBI) with keto (PNBI-СО) and sulfonic (PNBI-SO₂) bridging groups are prepared by the solid-phase polycyclization of films of corresponding polyaminoimides (PANI) synthesized by the polycondensation of 1,4,5,8-naphthalenetetracarboxylic dianhydride with 3,3',4,4'-tetraaminobenzophenone and 3,3',4,4'-tetraaminodiphenyl sulfone in N-methylpyrrolidone, respectively. The polycondensation process and the chemical structure of the resulting PANI and PNBI are controlled by ¹Н and ¹³С NMR and IR spectroscopy. It is shown that variation in the temperature of solid-state polycyclization allows for the synthesis of polymers with various cyclization degrees. The experimental values of gas permeability and diffusion coefficients for He, H₂, N₂, O₂, CO₂, and CH₄ are measured, and the solubility coefficients and ideal selectivity for various gas pairs are calculated. It is found that in terms of the permeability/selectivity ratio completely cyclized PNBI are advantageous over incompletely cyclized ones. This finding should be taken into account when choosing a polymer and a selective layer formation method to develop novel composite membranes. The gas transport characteristics achieved for completely cyclized PNBI-SO₂ and their good film-forming properties combined with a very high thermal stability of this class polymers are of great interest for further expanding the PNBI range and prospects for applying novel polymers of this class in various gas separation processes.