Fluoropolymers permselective membranes

Grafting of functional monomers onto fluoropolymers produced a wide variety of permselective membranes. Grafting of styrene (with the following sulfonation), (meth)acrylic acids, 4-vinylpyridine, A-vinylpyrrolidone onto PTFE films gave membranes for reverse omosis,32-34 ion-exchange membrane,35-39 membranes for separating water from organic solvents by pervaporation,49-42 as well as other kinds of valuable membranes. 

Virtually the entire membrane manufacture today is based on laminate structures comprising a thin barrier layer deployed upon a much thicker, highly permeable support. Most are formed of compositionaUy homogeneous polysulfone, cellulose acetate, polyamides, and various fluoropolymers by phase inversion techniques in which ultrathin films of suitably permselective material are deposited on prefabricated porous support structures. Hydrophobic polymers as polyethylene, polypropylene, or polysulfone are often used as supports. A fairly comprehensive hst of microporous and ultrafiltration commercial membranes and produced companies are presented in Refs [107-109]. A review on inorganic membranes has been given in Ref. [110]. 

Hyflon AD is an amorphous perfluorinated copolymer of tetrafluoroethylene (TFE) and 2,2,4-trifluoro-5-trifluoromethoxy-l,3-dioxole (TTD). Compared to the situation in the Teflon AF series, the reduced intermolecular distance due to the structural change result in moderate fractional free volume of 23%. Thus, the gas permeabilities are lower than those of Teflon AF membranes, allowing the increase of permselectivities. While this fluoropolymer has the advantage of solubility in fluorinated liquid, such as Galden FIT 55 and HFE 7100, the permeation properties are affected by the kind of residual solvents as well. 

---