Solid-state complexes of hexafluoro-2-propanol with benzophenone-containing polyimides

Films of benzophenone-containing polyimides were cast from hexafluoro-2-pro panol (HFIP) solutions and vacuum-dried just above the HFIP boiling tempera ture (59 degreesC) until a constant weight was achieved. Upon heating, the films exhibited 15% weight loss beginning around 150 degreesC. Using infrar ed spectroscopy, it was determined that the evolved gas was HFIP, and it fo rmed a hydrogen-bonded solid-state complex with the polyimide. The films st ill contained nearly 15% HFIP 18 months after casting, a testament to the r oom temperature stability of the complex. The HFIP-complexed polyimide film s 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 evidenc ed by a reduced storage modulus and glass transition temperature compared t o the uncomplexed polyimide.