Perfluoropolyethers (PFPEs) are a class of

organofluorine compound Organofluorine chemistry describes the chemistry of organofluorine compounds, organic compounds that contain a carbon–fluorine bond. Organofluorine compounds find diverse applications ranging from oil and water repellents to pharmaceuticals, ...

. Some types are synthetic liquid lubricants that have been used in the aerospace industry for over 30 years. The main properties of PFPE are being temperature resistant between and (depending on specific composites), having very low outgassing compared to other fluids (

vapour pressure Vapor pressure or equilibrium vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indicat ...

of ) and having a dielectric strength of around 15.7 MV/m. Perfluoropolyethers consists of a

polymer A polymer () is a chemical substance, substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeat unit, repeating subunits derived from one or more species of monomers. Due to their br ...

chain in which

monomer A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization. Classification Chemis ...

s consisting of perfluoro-

alkyl In organic chemistry, an alkyl group is an alkane missing one hydrogen. The term ''alkyl'' is intentionally unspecific to include many possible substitutions. An acyclic alkyl has the general formula of . A cycloalkyl group is derived from a cy ...

groups are joined by

ether In organic chemistry, ethers are a class of compounds that contain an ether group, a single oxygen atom bonded to two separate carbon atoms, each part of an organyl group (e.g., alkyl or aryl). They have the general formula , where R and R� ...

linkages. The bonds between

carbon Carbon () is a chemical element; it has chemical symbol, symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—meaning that its atoms are able to form up to four covalent bonds due to its valence shell exhibiting 4 ...

and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

fluorine Fluorine is a chemical element; it has Chemical symbol, symbol F and atomic number 9. It is the lightest halogen and exists at Standard temperature and pressure, standard conditions as pale yellow Diatomic molecule, diatomic gas. Fluorine is extre ...

are strong. Perfluoropolyethers are a type of

PFAS Per- and polyfluoroalkyl substances (also PFAS, PFASs, and informally referred to as "forever chemicals") are a group of synthetic organofluorine chemical compounds that have multiple fluorine atoms attached to an alkyl chain; there are 7 millio ...

. The thermal and chemical stability of PFPEs along with a

vapor–liquid equilibrium In thermodynamics and chemical engineering, the vapor–liquid equilibrium (VLE) describes the distribution of a chemical species between the vapor phase and a liquid phase. The Vapor quality, concentration of a vapor in contact with its liquid, ...

of 230 °C when mixed with the right composites make it a suitable candidate for vapor phase

soldering Soldering (; ) is a process of joining two metal surfaces together using a filler metal called solder. The soldering process involves heating the surfaces to be joined and melting the solder, which is then allowed to cool and solidify, creatin ...

technologies.

History

Perfluoropolyethers were developed in the early 1960s for the

USAF The United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...

, who needed a lubricant that would not react with

liquid Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...

or gaseous oxygen (O₂).

Manufacture

Each type of perfluoropolyether is synthesized differently: PFPE-K is obtained from HFPO by

anionic polymerization In polymer chemistry, anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of monomers initiated with anions. The type of reaction has many manifestations, but tradit ...

. For PFPE-Y and PFBE-Z, photooxidation of

hexafluoropropylene Hexafluoropropylene is the fluoroalkene with the formula CF3CF=CF2. It is the perfluorocarbon counterpart to the hydrocarbon propylene. It is mainly used to produce copolymers with tetrafluoroethylene. Hexafluoropropylene is used as a chemical i ...

and

tetrafluoroethylene Tetrafluoroethylene (TFE) is a fluorocarbon with the chemical formula . It is a colorless gas. Its structure is . It is used primarily in the industrial preparation of fluoropolymers. It is the simplest perfluorinated alkene. It was first repor ...

, respectively, is applied. PFPE-D is synthesized by anionic ring-opening polymerization of 2,2,3,3-tetrafluorooxetane. PFPE-A is obtained by an initial

esterification In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

polyethylene glycol Polyethylene glycol (PEG; ) is a polyether compound derived from petroleum with many applications, from industrial manufacturing to medicine. PEG is also known as polyethylene oxide (PEO) or polyoxyethylene (POE), depending on its molecular wei ...

with a perfluoroacyl fluoride. Then, it is converted into a fully fluorined polymer using direct fluorination. File:PFPE-K.svg, PFPE-K File:PFPE-Y.svg, PFPE-Y File:PFPE-Z.svg, PFPE-Z File:PFPE-D.svg, PFPE-D File:PFPE-A.svg, PFPE-A

Properties

PFPEs are chemically inert to many acids and

oxidant An oxidizing agent (also known as an oxidant, oxidizer, electron recipient, or electron acceptor) is a substance in a redox chemical reaction that gains or "Electron acceptor, accepts"/"receives" an electron from a (called the , , or ''electr ...

s (like fuming sulfuric acid (oleum, SO₃),

chlorine gas Chlorine is a chemical element; it has Symbol (chemistry), symbol Cl and atomic number 17. The second-lightest of the halogens, it appears between fluorine and bromine in the periodic table and its properties are mostly intermediate between ...

) and solvents, etc. PFPEs are nonflammable, and exhibit unusually high load carry capabilities. PFPEs can withstand gamma ray degradation. Electrical resistivity is 10¹⁴ ohm/cm ()

Toxicity

Do not breathe gas/fumes/vapor/spray. As this is a large class of chemicals, refer to the specific chemical's safety data sheet.

Applications

Generally, PFPEs may be used as lubricant in all sorts of bearing, plug valves, gaskets, chains, and joint bearing applications, where oxygen inertness of a material is a requirement. Examples include aircraft fuel systems, mechanical components of devices used in

airspace Airspace is the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere. It is not the same as outer space which is t ...

, deep space or high vacuum and at cryogenic temperatures. PFPEs may be used in mold release agent for plastic injection molding. As top coating lubricant on computer disc drives and Scanning Electron Microscope As anti-galling compounds. As fluid medium in ferrofluidic seals.

Semiconductor industry

In the semiconductor industry, PFPEs may be used as a vacuum grease or in

plasma etching Plasma etching is a form of plasma processing used to fabricate integrated circuits. It involves a high-speed stream of glow discharge (Plasma (physics), plasma) of an appropriate gas mixture being shot (in pulses) at a sample. The plasma source, ...

equipment, or for robots used in semiconductor wafer handling, clean rooms, and other commercial environments.

References

{{reflist Lubricants Perfluoropolyethers