Fluorinated ethylene propylene
Fluorinated Ethylene Propylene Copolymer (FEP) is a semi-crystalline perfluorinated polymer closely linked to PTFE being a copolymer of tetrafluoroethylene and hexafluoropropylene. Its properties are similar, but mostly a little low-grade to, those of PTFE but it has the excellent practical advantage of being melt-processable (though more expensive). Compared in more detail to PTFE, it has equally superior chemical resistance and electrical properties (up to very high frequencies) and good weathering resistance.
FEP is produced by free-radical polymerization of mixtures of tetrafluoroethylene and hexafluoropropylene. The mixture is biased to compensate for the relatively low reactivity of the propylene component. The process is typically initiated with peroxydisulfate, which homolyzes to generate sulfate radicals. Because FEP is poorly soluble in almost all solvents, the polymerization is conducted as an emulsion in water, often using a surfactant such as perfluorooctanesulfonic acid (PFOS). The polymer contains about 5% of the propylene component.
Applications of Fluorinated Ethylene Propylene Copolymer (FEP) include chemical and medical equipment, chemical apparatus, wire coverings, extruded insulation and glazing film for solar panels, and coatings and protective linings.