Editing Polyethylene glycol (section)

==Available forms and nomenclature==
''PEG'', ''PEO'', and ''POE'' refer to an [[oligomer]] or polymer of [[ethylene oxide]]. The three names are chemically synonymous, but historically ''PEG'' is preferred in the biomedical field, whereas ''PEO'' is more prevalent in the field of polymer chemistry. Because different applications require different polymer chain lengths, ''PEG'' has tended to refer to oligomers and polymers with a molecular mass below 20,000{{nbsp}}g/mol, ''PEO'' to polymers with a molecular mass above 20,000{{nbsp}}g/mol, and ''POE'' to a polymer of any molecular mass.<ref>For example, in the [http://www.scientificpolymer.com/utils/search.asp online catalog] {{webarchive|url=https://web.archive.org/web/20061229131736/http://www.scientificpolymer.com/utils/search.asp |date=29 December 2006 }} of Scientific Polymer Products, Inc., poly(ethylene glycol) molecular weights run up to about 20,000, while those of poly(ethylene oxide) have six or seven digits.</ref> PEGs are prepared by [[polymerization]] of [[ethylene oxide]] and are commercially available over a wide range of molecular weights from 300{{nbsp}}g/mol to 10,000,000{{nbsp}}g/mol.<ref name="French-2009"/>

PEG and PEO are liquids or low-melting solids, depending on their [[molecular weight]]s. While PEG and PEO with different molecular weights find use in different applications and have different physical properties (e.g. [[viscosity]]) due to chain length effects, their chemical properties are nearly identical. Different forms of PEG are also available, depending on the [[Radical initiator|initiator]] used for the polymerization process – the most common initiator is a monofunctional methyl ether PEG, or methoxypoly(ethylene glycol), abbreviated mPEG. Lower-molecular-weight PEGs are also available as purer oligomers, referred to as monodisperse, uniform, or discrete. Very high-purity PEG has recently been shown to be crystalline, allowing the determination of a crystal structure by [[x-ray crystallography]].<ref name="French-2009">{{cite journal | vauthors = French AC, Thompson AL, Davis BG | title = High-purity discrete PEG-oligomer crystals allow structural insight | journal = Angewandte Chemie | volume = 48 | issue = 7 | pages = 1248–52 | year = 2009 | pmid = 19142918 | doi = 10.1002/anie.200804623 | url = http://users.ox.ac.uk/~dplb0149/publication/pub108.pdf }}</ref> Since purification and separation of pure oligomers is difficult, the price for this type of quality is often 10–1000 fold that of polydisperse PEG.

PEGs are also available with different geometries.
* ''Branched'' PEGs have three to ten PEG chains emanating from a central core group.
* ''Star'' PEGs have 10 to 100 PEG chains emanating from a central core group.
* ''Comb'' PEGs have multiple PEG chains normally grafted onto a polymer backbone.

The numbers that are often included in the names of PEGs indicate their average molecular weights (e.g. a PEG with {{nowrap|''n'' {{=}} 9}} would have an average molecular weight of approximately 400 [[Atomic mass unit|daltons]], and would be labeled [[PEG 400]]). Most PEGs include molecules with a distribution of molecular weights (i.e. they are polydisperse). The size distribution can be characterized statistically by its [[weight average molecular weight]] (''M''<sub>w</sub>) and its [[number average molecular weight]] (''M''<sub>n</sub>), the ratio of which is called the [[polydispersity index]] (''Đ''<sub>M</sub>). ''M''<sub>w</sub> and ''M''<sub>n</sub> can be measured by [[mass spectrometry]].

[[PEGylation]] is the act of covalently coupling a PEG structure to another larger molecule, for example, a [[therapeutic protein]], which is then referred to as a ''PEGylated'' protein. [[PEGylated interferon alfa-2a]] or [[PEGylated interferon alfa-2b|alfa-2b]] are commonly used injectable treatments for [[hepatitis C]] infection.

PEG is soluble in [[water]], [[methanol]], [[ethanol]], [[acetonitrile]], [[benzene]], and [[dichloromethane]], and is insoluble in [[diethyl ether]] and [[hexane]]. It is coupled to hydrophobic molecules to produce non-ionic [[surfactant]]s.<ref>{{cite journal|title=Force-field dependence of the conformational properties of α,ω-dimethoxypolyethylene glycol|journal=Molecular Physics|volume=107|issue=13|pages=1313–1321|doi=10.1080/00268970902794826|year=2009| vauthors = Winger M, De Vries AH, Van Gunsteren WF |bibcode=2009MolPh.107.1313W|hdl=10072/37876|s2cid=97215923|hdl-access=free}}</ref>

[[File:SArfus PEO.3D.jpg|thumb|right|Polyethylene oxide (PEO, [[molar mass distribution|M<sub>w</sub>]] 4{{nbsp}}[[atomic mass unit|kDa]]) nanometric crystallites (4 nm)]]

PEG and related polymers (PEG phospholipid constructs) are often [[sonication|sonicated]] when used in biomedical applications. However, as reported by Murali et al., PEG is very sensitive to sonolytic degradation and PEG degradation products can be toxic to mammalian cells. It is, thus, imperative to assess potential PEG degradation to ensure that the final material does not contain undocumented contaminants that can introduce artifacts into experimental results.<ref>{{cite journal | vauthors = Murali VS, Wang R, Mikoryak CA, Pantano P, Draper R | title = Rapid detection of polyethylene glycol sonolysis upon functionalization of carbon nanomaterials | journal = Experimental Biology and Medicine | volume = 240 | issue = 9 | pages = 1147–51 | date = September 2015 | pmid = 25662826 | pmc = 4527952 | doi = 10.1177/1535370214567615 }}</ref>

PEGs and methoxypolyethylene glycols are manufactured by [[Dow Chemical Company|Dow Chemical]] under the trade name ''Carbowax'' for industrial use, and ''Carbowax Sentry'' for food and pharmaceutical use. They vary in consistency from liquid to solid, depending on the molecular weight, as indicated by a number following the name. They are used commercially in numerous applications, including foods, [[cosmetics]], pharmaceutics, [[biomedicine]], dispersing agents, solvents, [[ointment]]s, [[suppository]] bases, as tablet [[excipient]]s, and as [[laxative]]s. Some specific groups are [[lauromacrogol]]s, [[nonoxynol]]s, [[octoxynol]]s, and [[poloxamer]]s.