Synthesis and gas separation performances of intrinsically microporous polyimides based on 4-methylcatechol-derived monomers

Novel dibenzodioxane-containing dianhydride (MMBMDA) and diamine (FDBDA and MMBDA) monomers with sterically hindered contortion sites and pendent fluorene or trimethylbenzene moieties were prepared using 4-methylcatechol as a major reactant. High temperature polycondensation of these monomers and 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) enabled the synthesis of intrinsically microporous polyimides (PIM-PI) with adequately high molecular weights. The surface area, fractional free volume, and d-spacing of these PIM-PIs were 385–543 m2 g-1, 0.179-0.212, and 0.672-0.683 nm, respectively, following the order of MMBMDA-FDBDA > MMBMDA-MMBDA > 6FDA-FDBDA > 6FDA-MMBDA. Moreover, the high rigidity of MMBMDA-based PIM-PIs induced the formation of ultramicropores (<0.7 nm), which enhanced their gas-sieving capability. The PIM-PIs developed in this study showed favorable O2/N2, CO2/N2, and CO2/CH4 separation performances because of their rigid, sterically hindered and contorted architectures. In particular, MMBMDA-FDBDA exhibited comparable gas separation performances to the benchmark PIM-1 membrane.