View source for Perfluoropolyether

'''Perfluoropolyethers''' ('''PFPEs''') are a class of [[organofluorine compound]]. Some types are synthetic liquid lubricants that have been used in the aerospace industry for over 30 years.<ref>{{cite web |title=Spontaneous Dewetting of a Perfluoropolyether |publisher=[[National Aeronautics and Space Administration]] |author=Bradley Shogrin |date=August 1995 |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950026498.pdf |accessdate=November 29, 2017}}</ref> The main properties of PFPE are being temperature resistant between {{Convert|-58|C|K}} and {{Convert|257|C|K}} (depending on specific composites), having very low outgassing compared to other fluids ([[vapor pressure|vapour pressure]] of {{val|6|e=-8|ul=Torr}}) and having a dielectric strength of around 15.7&nbsp;MV/m.<ref>{{Cite web|url=http://www.solvay.com/en/markets-and-products/featured-products/Fomblin-PFPE-Lubricants.html|title = Fomblin® PFPE Lubricants}}</ref>

Perfluoropolyethers consists of a [[polymer]] chain in which [[monomer]]s consisting of [[perfluoro]]-[[alkyl]] groups are joined by [[ether]] linkages. The bonds between [[carbon]] and [[oxygen]] or [[fluorine]] are strong.<ref name="topda">{{cite news |title=Brief Introduction of PFPE Synthesis Methods |author=Fluorochemie |publisher=Fuzhou Topda New Material Co., Ltd. |url=https://www.fluorochemie.com/brief-introduction-of-pfpe-synthesis-methods.html |accessdate=June 27, 2022}}</ref> Perfluoropolyethers are a type of [[PFAS]].<ref>{{cite journal |last1=Kwiatkowski |first1=Carol F. |last2=Andrews |first2=David Q. |last3=Birnbaum |first3=Linda S. |last4=Bruton |first4=Thomas A. |last5=DeWitt |first5=Jamie C. |last6=Knappe |first6=Detlef R. U. |last7=Maffini |first7=Maricel V. |last8=Miller |first8=Mark F. |last9=Pelch |first9=Katherine E. |last10=Reade |first10=Anna |last11=Soehl |first11=Anna |last12=Trier |first12=Xenia |last13=Venier |first13=Marta |last14=Wagner |first14=Charlotte C. |last15=Wang |first15=Zhanyun |last16=Blum |first16=Arlene |title=Scientific Basis for Managing PFAS as a Chemical Class |journal=Environmental Science & Technology Letters |date=11 August 2020 |volume=7 |issue=8 |pages=532–543 |doi=10.1021/acs.estlett.0c00255|doi-access=free |hdl=20.500.11850/438999 |hdl-access=free }}</ref>

The thermal and chemical stability of PFPEs along with a [[vapor–liquid equilibrium]] of 230&nbsp;°C when mixed with the right composites make it a suitable candidate for vapor phase [[reflow soldering|soldering]] technologies.<ref>{{Cite web |url=https://www.asscon.de/d/pages/aktuelles/pdf/lead-free%20proc.pdf |title=Archived copy |access-date=2020-08-23 |archive-date=2021-02-27 |archive-url=https://web.archive.org/web/20210227165041/https://www.asscon.de/d/pages/aktuelles/pdf/lead-free%20proc.pdf |url-status=dead }}</ref>

== History ==
Perfluoropolyethers were developed in the early 1960s for the [[United States Air Force|USAF]], who needed a lubricant that would not react with [[Liquid oxygen|liquid]] or [[Oxygen|gaseous oxygen]] (O<sub>2</sub>).<ref name=":0">{{Cite web |title=HUSKEY Specialty lubricants |url=https://www.huskey.ru/APPLICATIONS%20AND%20BENEFITS%20OF%20PERFLUOROPOLYETHER.pdf |publisher=HUSK-ITT Corporation}}</ref>

==Manufacture==
Each type of perfluoropolyether is synthesized differently: PFPE-K is obtained from [[HFPO]] by [[anionic polymerization]]. For PFPE-Y and PFBE-Z, [[photooxidation]] of [[hexafluoropropylene]] and [[tetrafluoroethylene]], 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]] of [[polyethylene glycol]] with a perfluoroacyl fluoride. Then, it is converted into a fully fluorined polymer using direct fluorination.<ref name="topda"/><ref>{{Cite book |url=https://www.oecd.org/chemicalsafety/risk-management/synthesis-report-understanding-perfluoropolyethers-and-their-life-cycle.pdf |title=Synthesis Report on Understanding Perfluoropolyethers (PFPEs) and Their Life Cycle |date=2024 |publisher=OECD}}</ref>
<gallery widths="250"caption="Structural formulas of different types">
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
</gallery>

==Properties==
PFPEs are chemically inert to many acids and [[oxidant]]s (like [[Oleum|fuming sulfuric acid]] (oleum, [[Sulfur trioxide|SO<sub>3</sub>]]), [[chlorine gas]], [[oxygen]]) and solvents, etc.

PFPEs are non-toxic under normal conditions, nonflammable, and exhibit unusually high load carry capabilities.<ref name=":0" /><ref name=":1">{{Cite book |last=Ash |first=Michael |url=https://www.worldcat.org/oclc/747426845 |title=Handbook of green chemicals |date=2004 |publisher=Synapse Information Resources |others=Irene Ash |isbn=978-1-934764-29-9 |edition=2 |location=Endicott, NY |oclc=747426845}}</ref>{{Rp|page=275}}
PFPEs can withstand gamma ray degradation.<ref name=":0" />

Electrical resistivity is 10<sup>14</sup> ohm/cm ({{convert|20|C|F}})<ref name=":0" />

== Applications ==
Generally, PFPEs may be used as lubricant in all sorts of bearing, [[plug valve]]s, gaskets, chains, and joint bearing applications, where oxygen inertness of a material is a requirement.<ref name=":0" /><ref name=":1" /> Examples include aircraft fuel systems, mechanical components of devices used in [[airspace]], deep space or high vacuum and at cryogenic temperatures.<ref name=":0" />

PFPEs may be used in mold release agent for [[plastic injection molding]].<ref name=":0" />

As top coating lubricant on computer disc drives and Scanning Electron Microscope<ref name=":0" />{{r|:1|p=275}}

As [[Galling|anti-galling]] compounds.<ref name=":0" />

As fluid medium in [[ferrofluidic seal]]s.<ref name=":0" />

=== Semiconductor industry ===
In the semiconductor industry, PFPEs may be used as a [[vacuum grease]] or in [[plasma etching]] equipment, or for robots used in semiconductor [[Wafer (electronics)|wafer]] handling, clean rooms, and other commercial environments.<ref name=":0" />

== See also ==
* [[Krytox]], a PFPE-based lubricant

==References==
{{reflist}}

[[Category:Lubricants]]
[[Category:Perfluoropolyethers]]