Zhao Hong, Zhang Jie, Wu Nianqiang, Zhang Xu, Crowley Katie, Weber Stephen G
Department of Chemistry, University of Pittsburgh, Pennsylvania 15260, USA.
J Am Chem Soc. 2005 Nov 2;127(43):15112-9. doi: 10.1021/ja052875p.
Fluorous media have great potential for selective extraction (e.g., as applied to organic synthesis). Fluorous polymer films would have significant advantages in fluorous separations. Stable films of Teflon AF 2400 were cast from solution. Films appear defect-free (SEM; AFM). Rigid aromatic solutes are transported (from chloroform solution to chloroform receiving phase) in a size-dependent manner (log permeability is proportional to -0.0067 times critical volume). Benzene's permeability is about 2 orders of magnitude higher than in comparable gas-phase experiments. The films show selectivity for fluorinated solutes in comparison to the hydrogen-containing control. Transport rates are dependent on the solvent making up the source and receiving phases. The effect of solvent is, interestingly, not due to changes in partition ratio, but rather it is due to changes in the solute diffusion coefficient in the film. Solvents plasticize the films. A less volatile compound, -COOH-terminated poly(hexafluoropropylene oxide) (4), plasticizes the films (T(g) = -40 degrees C). Permeabilities are decreased in comparison to 4-free films apparently because of decreased diffusivity of solutes. The slope of dependence of log permeability on critical volume is not changed, however.
氟介质在选择性萃取方面具有巨大潜力（例如，应用于有机合成）。含氟聚合物膜在氟分离中具有显著优势。由溶液浇铸出了稳定的聚四氟乙烯AF 2400膜。膜看起来无缺陷（扫描电子显微镜；原子力显微镜）。刚性芳香族溶质以尺寸依赖的方式（从氯仿溶液传输到氯仿接收相）进行传输（对数渗透率与临界体积的-0.0067倍成正比）。苯的渗透率比在类似的气相实验中高约2个数量级。与含氢对照物相比，这些膜对含氟溶质具有选择性。传输速率取决于构成源相和接收相的溶剂。有趣的是，溶剂的影响并非由于分配比的变化，而是由于溶质在膜中的扩散系数的变化。溶剂使膜发生增塑。一种挥发性较小的化合物，-COOH封端的聚（六氟环氧丙烷）（4），使膜增塑（玻璃化转变温度T(g)= -40℃）。与不含4的膜相比，渗透率降低显然是因为溶质的扩散率降低。然而，对数渗透率对临界体积的依赖斜率并未改变。
