Films of benzophenone-containing polyimides were cast from hexafluoro-2-propanol (HFIP) solutions and vacuum-dried just above the HFIP boiling temperature (59 degreesC) until a constant weight was achieved. Upon heating, the films exhibited 15% weight loss beginning around 150 degreesC. Using infrared spectroscopy, it was determined that the evolved gas was HFIP, and it formed a hydrogen-bonded solid-state complex with the polyimide. The films still contained nearly 15% HFIP 18 months after casting, a testament to the room temperature stability of the complex. The HFIP-complexed polyimide films exhibited higher gas permeabilities and reduced selectivities compared to the same polyimide cast from dimethylformamide. These transport properties were attributed to plasticization of the polyimide by the HFIP, as evidenced by a reduced storage modulus and glass transition temperature compared to the uncomplexed polyimide.