Polybenzimidazole (PBI) is highly selective for H2 removal from mixtures with CO2, but it exhibits low gas permeabilities. Celazole® PBI was blended with more permeable HAB-6FDA-CI, an ortho-functional thermally rearrangeable polyimide, to improve its gas permeabilities while attempting to maintain high selectivity. A compatibilizer, 1-methylimidazole, enhanced phase dispersion when added to the casting solutions. Films containing 20–40 wt% polyimide exhibited a matrix-droplet morphology as observed by scanning and transmission electron microscopy. Heat treatment at 400 °C under inert atmosphere thermally rearranged the polyimide in the blends. After heat treatment, H2/CO2 selectivities at 35 °C doubled for Celazole® and 20–33 wt% polyimide compatibilized blends, exceeding the 2008 upper bound. Simultaneous increases in both H2 permeability and H2/CO2 selectivity were observed after heat treatment for the 33/67 wt% HAB-6FDA-CI/Celazole® compatibilized blend, which exhibited over twice the H2 permeability of Celazole® and similar selectivity. Heat treatment reduced free volume and induced para-crystallinity in the PBI phase of the blends as evidenced by x-ray scattering. Thermally treated blend films were mechanically flexible and exhibited elastic moduli and tensile strengths similar to Celazole®, despite having low elongation at break.
