How fluorous is poly(2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxide-co-tetrafluoroethylene) (Teflon AF)?

We investigated poly(2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxide-co-tetrafluoroethylene (Teflon AF 2400, Tg = 240 degrees C), a stable and permeable fluorous polymer, as a transport/extraction medium for solutes for the first time. From the study of transport behavior of a series of solutes (in chloroform solution) through the film, and detailed measurement of the partitioning and diffusion of benzene in the film, we showed that the Teflon AF film is influenced by the solvent to which it is exposed. In particular, the solvent chloroform is sorbed in the film at a high concentration of 1.13 M. This plasticizes the film, so that the diffusion coefficient of benzene is about 3 orders of magnitude larger in a chloroform-equilibrated film compared to benzene coming from the gas phase into a "dry" film. The partition ratio of the polar solute 3-hydroxypyridine is dramatically higher in the case of partitioning between chloroform and a film (0.02) compared to partitioning between chloroform and the fluorous solvent FC-72 (6.7 x 10-5). Krytox FSH, a carboxylic acid terminated perfluoropolyether, plasticizes films. Tg in a 50% (w/w) film decreases to -40 degrees C. This carboxylic acid is capable of molecular recognition in the film. The noncovalent association between Krytox FSH (0.13 M in the film) and 3-hydroxypyridine increases the distribution ratio of the polar solute into the film by 41 times. In comparison, the partition ratio into a fluorocarbon solvent (FC-72) increases 15 000 times under the same conditions. As a result of imbibing organic solvent, the films of Teflon AF 2400 are not as fluorous as a fluorous liquid.