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This study reports the preparation and characterization of a carbon molecular sieve membrane (CMSM-600) derived from a processable high molecular weight fluorinated polybenzimidazole (PBI-6F). This CMSM-600 exhibits excellent separation performance for several gas pairs. CMSM-600 permeability for CO2was more than 300 times higher than the permeability of PBI-6F, with around a 1.5-fold increase in the CO2/CH4selectivity. These values (PCO2= 7920 Barrer, αCO2/CH4= 75) were well above the 2008 Robeson upper limit. The structure of the CMSM-600 was studied by Raman, XPS, and XRD analyses. The XPS spectroscopy showed the formation of pyrrole- and pyrazine-type units within the same strand promoting a less compact structure, which would explain its high permeability values as compared to those found for other polybenzimidazole derivatives. The improvement in gas separation properties can be attributed to the formation of more open micropores maintaining the ultramicropores during the pyrolysis of PBI-6F.