Polyethylene glycol
147203
225631058
2008-07-14T17:19:38Z
64.15.230.129
/* Other uses */ reworded for accuracy: use of PEG in polyurethanes
{{Chembox new
| ImageFile = Polyethylene glycol chemical structure.png
| ImageSize = 188
| IUPACName = poly(oxyethylene) <small>{structure-based}</small>,<br> poly(ethylene oxide) <small>{source-based}</small><ref>J. KAHOVEC, R. B. FOX and K. HATADA; “Nomenclature of regular single-strand organic polymers (IUPAC Recommendations 2002)”; Pure and Applied Chemistry; IUPAC; 2002; 74 (10): pp. 1921–1956.</ref>
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| Section1 = {{Chembox Identifiers
| CASNo = 25322-68-3
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| Section2 = {{Chembox Properties
| Formula = C<sub>2n</sub>H<sub>4n+2</sub>O<sub>n+1</sub>
| MolarMass = 44n+18
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| Section3 = {{Chembox Hazards
| MainHazards =
| FlashPt = 182 - 287 °C
| Autoignition =
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}}
'''Poly([[ethylene glycol]])''' (PEG), also known as '''poly([[ethylene oxide]])''' (PEO) or polyoxyethylene (POE), are the most commercially important [[Ether|polyethers]]. PEG, PEO or POE refers to an [[oligomer]] or polymer of ethylene oxide. The three names are chemically synonymous, but historically PEG has tended to refer to oligomers and polymers with a molecular mass below 20,000 g/mol, PEO refers to polymers with a molecular mass above 20,000 g/mol, and POE refers to a polymer of any molecular mass.<ref>For example, in the online catalog[http://www.scientificpolymer.com/utils/search.asp] of Scientific Polymer Products, Inc., poly(ethylene glycol) molecular weights run up to about 20,000, while those of poly(ethylene oxide) have 6 or 7 digits.</ref> PEG and PEO are liquids or low-melting solids, depending on their [[molecular weight]]s. PEGs are prepared by polymerization of [[ethylene oxide]] and are commercially available over a wide range of molecular weights from 300 g/mol to 10,000,000 g/mol. 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 dependent on the [[initiator]] used for the polymerization process. The most common of which is a monofunctional methyl ether PEG (methoxypoly(ethylene glycol)), abbreviated mPEG. PEGs are also available with different geometries. ''Branched'' PEGs have 3 to 10 PEG chains emanating from a central core group. ''Star'' PEGs have 10 - 100 PEG chains emanating from a central core group. ''Comb'' PEGs have multiple PEG chains normally grafted to a polymer backbone.
Their melting points vary depending on the Formula Weight of the polymer. PEG or PEO has the following structure:
:HO-(CH<sub>2</sub>-CH<sub>2</sub>-O-)<sub>n</sub>-H
The numbers that are often included in the names of PEGs indicate their average molecular weights, e.g. a PEG with n=80 would have an average molecular weight of approximately 3500 [[Atomic mass unit|daltons]] and would be labeled PEG 3500. 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]] (Mw) and its [[number average molecular weight]] (Mn), the ratio of which is called the [[polydispersity index]] (Mw/Mn). Mw and Mn can be measured by [[mass spectroscopy]].
[[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 '''PEGylated'''). [[PEGylated interferon alfa-2a]] or -2b is a commonly used injectable treatment for [[Hepatitis C]] infection.
PEG is soluble in [[water]], [[methanol]], [[benzene]], [[dichloromethane]] and is insoluble in [[diethyl ether]] and [[hexane]]. It is coupled to hydrophobic molecules to produce non-ionic [[surfactant]]s.
==Production==
Poly (ethylene glycol) is produced by the interaction of [[ethylene oxide]] with water, [[ethylene glycol]] or ethylene glycol oligomers.[http://chemindustry.ru/Polyethylene_Glycol.php] The reaction is catalyzed by acidic or basic catalysts. Ethylene glycol and its oligomers are preferable as a starting material instead of water, because it allows the creation of polymers with a low [[polydispersity]] (narrow molecular weight distribution). Polymer chain length depends on the ratio of reactants.
'''HOCH<sub>2</sub>CH<sub>2</sub>OH + n(CH<sub>2</sub>CH<sub>2</sub>O) → HO(CH<sub>2</sub>CH<sub>2</sub>O)<sub>n+1</sub>H'''
Depending on the catalyst type, the mechanism of polymerization can be cationic or anionic. The anionic mechanism is preferable because it allows one to obtain PEG with a low [[polydispersity]]. [[Polymerization]] of ethylene oxide is an exothermic process. Overheating or contaminating ethylene oxide with catalysts such as alkalis or metal oxides can lead to runaway polymerization which can end with an explosion after few hours.
Polyethylene oxide or high-molecular polyethylene glycol is synthesized by [[suspension polymerization]]. It is necessary to hold the growing polymer chain in solution in the course of the polycondensation process. The reaction is catalyzed by magnesium-, aluminium- or calcium-organoelement compounds. To prevent [[coagulation]] of polymer chains from solution, chelating additives such as [[dimethylglyoxime]] are used.
Alkali catalysts such as [[sodium hydroxide]] NaOH, [[potassium hydroxide]] KOH or [[sodium carbonate]] Na<sub>2</sub>CO<sub>3</sub> are used to prepare low-molecular polyethylene glycol.
==Clinical uses==
Polyethylene glycol has a low toxicity<ref>{{cite book | author = Victor O. Sheftel | title = Indirect Food Additives and Polymers: Migration and Toxicology | year = 2000 | pages = 1114-1116 | publisher = CRC | url = http://www.mindfully.org/Plastic/Polymers/Polyethylene-Glycols-PEGs.htm}}</ref> and is used in a variety of products. It is the basis of a number of [[laxative]]s (e.g. [[macrogol]]-containing products such as [[Movicol]] and polyethylene glycol 3350, or MiraLax or GlycoLax). It is the basis of many [[skin cream]]s, as ''cetomacrogol'', and [[sexual lubricant]]s, frequently combined with [[glycerin]]. [[Whole bowel irrigation]] (polyethylene glycol with added electrolytes) is used for bowel preparation before [[surgery]] or [[colonoscopy]] and drug overdoses. It is sold under the brand names '''GoLYTELY''', '''GlycoLax''', '''Fortrans''', '''TriLyte''', and '''Colyte'''. When attached to various protein [[medication]]s, polyethylene glycol allows a slowed clearance of the carried protein from the blood. This makes for a longer acting medicinal effect and reduces [[toxicity]], and it allows longer dosing intervals. Examples include PEG-[[interferon|interferon alpha]] which is used to treat [[hepatitis C]] and PEG-[[filgrastim]] (Neulasta) which is used to treat [[neutropenia]]. It has been shown that polyethylene glycol can improve healing of [[vertebral column|spinal]] injuries in dogs.<ref>{{cite news | url = http://seattlepi.nwsource.com/health/202292_spinal04.html | date = 4 December 2004 | title = Study on dogs yields hope in human paralysis treatment | author = Lee Bowman | publisher = seattlepi.com}}</ref> One of the earlier findings that polyethylene glycol can aid in nerve repair came from the University of Texas (Krause and Bittner).<ref>{{cite journal | author = T. L. Krause and G. D. Bittner | title = Rapid Morphological Fusion of Severed Myelinated Axons by Polyethylene Glycol | year = 1990 | journal = [[PNAS]] | volume = 87 | issue = 4 | pages = 1471–1475 | doi = 10.1073/pnas.87.4.1471 | pmid = 2304913}}</ref> Polyethylene glycol is commonly used to fuse B-cells with [[myeloma]] cells in [[monoclonal antibody]] production. PEG has recently been proved to give better results in [[constipation]] patients than [[tegaserod]].<ref> Di Palma JA et al. Am J Gastroenterol 2007 Sep 102:1964 </ref>
===Research for New Clinical Uses===
* High-molecular weight PEG, e.g., PEG 8000, is a strikingly potent dietary preventive agent against [[colorectal cancer]] in animal models.<ref>{{cite journal | author = D. E. Corpet, G. Parnaud, M. Delverdier, G. Peiffer and S. Tache | title = Consistent and Fast Inhibition of Colon Carcinogenesis by Polyethylene Glycol in Mice and Rats Given Various Carcinogens | year = 2000 | journal = [[Cancer Res]] | volume = 60 | issue = 12 | pages = 3160–3164 | url = http://cancerres.aacrjournals.org/cgi/content/full/60/12/3160 | pmid = 10866305}}</ref>
The [http://www.inra.fr/reseau-nacre/sci-memb/corpet/indexan.html Chemoprevention Database] shows it is the most effective agent to suppress chemical carcinogenesis in rats. Cancer prevention in humans has not yet been tested in clinical trials.
* The injection of PEG 2000 into the bloodstream of guinea pigs after spinal cord injury leads to rapid recovery through molecular repair of nerve membranes.<ref>{{cite journal | author = R. B. Borgens and D. Bohnert | title = Rapid recovery from spinal cord injury after subcutaneously administered polyethylene glycol | year = 2001 | journal = [[Journal of Neuroscience Research]] | volume = 66 | issue = 6 | pages = 1179–1186 | doi = 10.1002/jnr.1254}}</ref> The effect of this treatment to prevent [[paraplegia]] in humans after an accident is not known yet.
* Research is being done in the use of PEG to mask antigens on red blood cells. Various research institutes have reported that using PEG can mask antigens without damaging the functions and shape of the cell.
PEG is being used in the repair of motor neurons damaged in crush or laceration incidence in vivo and in vitro. When coupled with melatonin, 75% of damaged sciatic nerves were rendered viable.<ref>{{cite journal | author= G. Bittner el. al.|journal= Neouroscience Letters |volume=376|year= 2005|pages= 98–101.
| doi = 10.1016/j.neulet.2004.11.033
| title = Melatonin enhances the in vitro and in vivo repair of severed rat sciatic axons}}</ref>
==Other uses==
PEG is used in a number of [[toothpaste]]s as a [[dispersant]]; it binds water and helps keep [[Xanthan gum|gum]] uniform throughout the toothpaste. It is also under investigation for use in [[body armor]]<ref>{{Cite news | author = Tonya Johnson | title = Army Scientists, Engineers develop Liquid Body Armor | url = http://www4.army.mil/ocpa/read.php?story_id_key=5872 | date = 21 April 2004}}</ref> and [[tattoo]]s to monitor [[diabetes]].<ref>{{cite news | publisher = [[BBC News]] | date = 1 September 2002 | title = Tattoo to monitor diabetes | url = http://news.bbc.co.uk/2/hi/health/2225404.stm}}</ref>
Polymer segments derived from PEG [[polyols]] impart flexibility to [[polyurethane]]s for applications such as elastomeric [[fiber]]s ([[spandex]]) and [[foam]] cushions.
Since PEG is a flexible, water-soluble polymer, it can be used to create very high [[osmotic pressure]]s (tens of atmospheres). It also is unlikely to have specific interactions with biological chemicals. These properties make PEG one of the most useful molecules for applying osmotic pressure in [[biochemistry]] experiments, particularly when using the [[osmotic stress technique]].{{Fact|date=July 2007}}
PEO (poly (ethylene oxide)) can serve as the separator and [[electrolyte]] [[solvent]] in [[lithium polymer cell]]s. Its low [[diffusion|diffusivity]] often requires high temperatures of operation, but its high viscosity even near its [[melting point]] allows very thin electrolyte layers. While [[crystallization]] of the polymer can degrade performance, many of the salts used to carry charge can also serve as a [[kinetic barrier]] to the formation of crystals. Such batteries carry greater energy for their weight than other [[lithium ion battery]] technologies.
When working with [[phenol]] in a laboratory situation, PEG 300 can be used on phenol skin burns to deactivate any residual phenol.
Poly (ethylene glycol) is also commonly used as a polar stationary phase for [[gas chromatography]], as well as a [[heat transfer fluid]] in electronic testers.
PEG is included in many or all formulations of the soft drink [[Dr Pepper]], purportedly as an anti-foaming agent. [citation needed]
PEG has also been used to preserve objects which have been salvaged from underwater, as was the case with the warship [[Regalskeppet Vasa|Vasa]] in Stockholm.<ref>Lars-Åke Kvarning, Bengt Ohrelius (1998), ''The Vasa - The Royal Ship'', ISBN 91-7486-581-1, pp. 133-141</ref> It replaces water in wooden objects, which makes the wood dimensionally stable and prevents warping or shrinking of the wood.
PEG is often seen (as a side effect) in mass spectrometry experiments with characteristic fragmentation patterns.
In the field of [[microbiology]], PEG precipitation is used to concentrate viruses and PEG is also used to induce complete fusion (mixing of both inner and outer leaflets) in liposomes reconstituted in vitro.
PEG is also used in lubricant eye drops. PEG derivatives such as [[narrow range ethoxylate]]s are used as [[surfactant]]s.
Dimethyl ethers of PEG are the key ingredient of [[Selexol]], a solvent used by coal-burning, integrated gasification [[combined cycle]] (IGCC) power plants to remove [[carbon dioxide]] and [[hydrogen sulfide]] from the gas waste stream.
[[Polymersome]]s can be PEG coated to make them invisible to white blood cells so they can carry medicine throughout the body.
==References==
{{reflist}}
==External links==
*
* [http://chemindustry.ru/Polyethylene_Glycol.php polyethylene glycol - chemical product info: properties, production, applications.]
==See also==
*[[PEGylation]]
[[Category:Polyethers]]
[[Category:Laxatives]]
[[Category:Solvents]]
[[Category:Coolants]]
[[Category:Polymers]]
[[de:Polyethylenglykol]]
[[fr:Macrogol]]
[[it:Glicole polietilenico]]
[[nl:Polyethyleenglycol]]
[[ja:ポリエチレングリコール]]
[[pl:Poli(tlenek etylenu)]]
[[pt:Polietilenoglicol]]
[[ru:Полиэтиленгликоль]]
[[sv:Polyetylenglykol]]