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Polyethylene glycol

Article Discussion

Template:Short description Template:Distinguish Template:For Template:Use dmy dates Template:Chembox Polyethylene glycol (PEG; Template:IPAc-en) 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 weight. The structure of PEG is commonly expressed as H−(O−CH2−CH2)n−OH.<ref name="Ullmann'Encyclo-2000">Template:Ullmann</ref>

PEG is commonly incorporated into hydrogels which present a functional form for further use. <ref name="b150">Template:Cite journal</ref>

UsesEdit

Medical usesEdit

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  • Pharmaceutical-grade PEG is used as an excipient in many pharmaceutical products, in oral, topical, and parenteral dosage forms.<ref>{{#invoke:citation/CS1|citation

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  • PEG is the basis of a number of laxatives (as MiraLax, RestoraLAX, MoviPrep, etc.).<ref name="Kean-2017" /> Whole bowel irrigation with polyethylene glycol and added electrolytes is used for bowel preparation before surgery or colonoscopy or for children with constipation.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> Macrogol (with brand names such as Laxido, Movicol and Miralax) is the generic name for polyethylene glycol used as a laxative. The name may be followed by a number that represents the average molecular weight (e.g. macrogol 3350, macrogol 4000, or macrogol 6000).

|CitationClass=web }}</ref> PEG could trigger allergic reaction,<ref name="Cabanillas-2021">Template:Cite journal</ref> and allergic reactions are the driver for both the United Kingdom and Canadian regulators to issue an advisory, noting that: two "individuals in the U.K. ... were treated and have recovered" from anaphylactic shock.<ref name="Bostock-2020">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="HealthCanada-2020">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The US CDC stated that in their jurisdiction six cases of "severe allergic reaction" had been recorded from more than 250,000 vaccinations, and of those six only one person had a "history of vaccination reactions".<ref name="Furtula-2020">Template:Cite news</ref>

Chemical usesEdit

File:MaryRose-conservation2.jpg
The remains of the 16th century carrack Mary Rose undergoing conservation treatment with PEG in the 1980s
File:Terra Cotta Warriors, Guardians of China’s First Emperor 1.jpg
Terra cotta warrior, showing traces of original color
  • Polyethylene glycol can serve as a green reaction medium in a variety of organic reactions.<ref>Template:Cite journal</ref>
  • Polyethylene 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 frequently used to preserve waterlogged wood and other organic artifacts that have been salvaged from underwater archaeological contexts, as was the case with the warship Vasa in Stockholm,<ref>Template:Cite book</ref> and similar cases. It replaces water in wooden objects, making the wood dimensionally stable and preventing the warping or shrinking of the wood when it dries.<ref name="Kean-2017"/> In addition, PEG is used when working with green wood as a stabilizer, and to prevent shrinkage.<ref>{{#invoke:citation/CS1|citation

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  • PEG has been used to preserve the painted colors on Terracotta Warriors unearthed at a UNESCO World Heritage site in China.<ref>{{#invoke:citation/CS1|citation

|CitationClass=web }}</ref> These painted artifacts were created during the Qin Shi Huang (first emperor of China) era. Within 15 seconds of the terra-cotta pieces being unearthed during excavations, the lacquer beneath the paint begins to curl after being exposed to the dry Xi'an air. The paint would subsequently flake off in about four minutes. The German Bavarian State Conservation Office developed a PEG preservative that when immediately applied to unearthed artifacts has aided in preserving the colors painted on the pieces of clay soldiers.<ref>Template:Cite journal</ref>

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Biological usesEdit

Commercial usesEdit

|CitationClass=web }}</ref> – its INS number is 1521<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> or E1521 in the EU.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

Industrial usesEdit

  • A nitrate ester-plasticized polyethylene glycol (NEPE-75) is used in Trident II submarine-launched ballistic missile solid rocket fuel.<ref name="Spinardi-1994">Template:Cite book</ref>
  • 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 syngas stream.
  • PEG has been used as the gate insulator in an electric double-layer transistor to induce superconductivity in an insulator.<ref>Template:Cite journal</ref>
  • PEG is used as a polymer host for solid polymer electrolytes. Although not yet in commercial production, many groups around the globe are engaged in research on solid polymer electrolytes involving PEG, to improve their properties, and in permitting their use in batteries, electro-chromic display systems, and other products in the future.
  • PEG is injected into industrial processes to reduce foaming in separation equipment.
  • PEG is used as a binder in the preparation of technical ceramics.<ref>Schneider, Samuel J. (1991) Engineered Materials Handbook: Ceramics and Glasses, Vol. 4. ASM International. Template:ISBN. p. 49.</ref>
  • PEG was used as an additive to silver halide photographic emulsions.
  • PEG is used as an active ingredient in agricultural soil wetter, which improves water-retention and seedling growth.<ref>{{#invoke:citation/CS1|citation

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Entertainment usesEdit

Human health effectsEdit

PEO'sTemplate:Clarify have "very low single dose oral toxicity", on the order of tens of grams per kilogram of human body weight when ingested by mouth.<ref name="Ullmann'Encyclo-2000"/> Because of its low toxicity, PEO is used in a variety of edible products.<ref>Template:Cite book</ref> It is also used as a lubricating coating for various surfaces in aqueous and non-aqueous applications.<ref>Template:Cite journal</ref>

The precursor to PEGs is ethylene oxide, which is hazardous.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Ethylene glycol and its ethers are nephrotoxic (poisonous to the kidneys) if applied to damaged skin.<ref name="Andersen-1999">Template:Cite journal</ref>

The United States Food and Drug Administration (FDA or US FDA) regards PEG as biologically inert and safe.<ref name="n551">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

A 2015 study appears to challenge the FDA's conclusion. In the study, a high-sensitivity ELISA assay detected anti-PEG antibodies in 72% of random blood plasma samples collected from 1990 to 1999. According to the study's authors, this result suggests that anti-PEG antibodies may be present, typically at low levels, in people who were never treated with PEGylated drugs.<ref>Template:Cite journal</ref><ref name="Yang-2016">Template:Cite journal</ref> Due to its ubiquity in many products and the large percentage of the population with antibodies to PEG, which indicates an allergic reaction, hypersensitive reactions to PEG are an increasing health concern.<ref name="Wenande-2016">Template:Cite journal</ref><ref>Template:Cite journal</ref> Allergy to PEG is usually discovered after a person has been diagnosed with an allergy to several seemingly unrelated products—including processed foods, cosmetics, drugs, and other substances—that contain or were manufactured with PEG.<ref name="Wenande-2016" />

Available forms and nomenclatureEdit

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 20,000Template:Nbspg/mol, PEO to polymers with a molecular mass above 20,000Template:Nbspg/mol, and POE to a polymer of any molecular mass.<ref>For example, in the online catalog Template:Webarchive 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 300Template:Nbspg/mol to 10,000,000Template:Nbspg/mol.<ref name="French-2009"/>

PEG and PEO are liquids or low-melting solids, depending on their molecular weights. 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 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">Template:Cite journal</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 Template:Nowrap would have an average molecular weight of approximately 400 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 (Mw) and its number average molecular weight (Mn), the ratio of which is called the polydispersity index (ĐM). Mw and Mn 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 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 surfactants.<ref>Template:Cite journal</ref>

File:SArfus PEO.3D.jpg
Polyethylene oxide (PEO, Mw 4Template:NbspkDa) nanometric crystallites (4 nm)

PEG and related polymers (PEG phospholipid constructs) are often 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>Template:Cite journal</ref>

PEGs and methoxypolyethylene glycols are manufactured by 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, ointments, suppository bases, as tablet excipients, and as laxatives. Some specific groups are lauromacrogols, nonoxynols, octoxynols, and poloxamers.

ProductionEdit

File:Polyethylene glycol 400.jpg
Polyethylene glycol 400, pharmaceutical quality
File:Polyethylene glycol 4000.jpg
Polyethylene glycol 4000, pharmaceutical quality

The production of polyethylene glycol was first reported in 1859. Both A. V. Lourenço and Charles Adolphe Wurtz independently isolated products that were polyethylene glycols.<ref name="Bailey-1990">Template:Cite book</ref> Polyethylene glycol is produced by the interaction of ethylene oxide with water, ethylene glycol, or ethylene glycol oligomers.<ref>Polyethylene glycol, Chemindustry.ru</ref> The reaction is catalyzed by acidic or basic catalysts. Ethylene glycol and its oligomers are preferable as a starting material instead of water because they allow the creation of polymers with a low polydispersity (narrow molecular weight distribution). Polymer chain length depends on the ratio of reactants.

HOCH2CH2OH + n(CH2CH2O) → HO(CH2CH2O)n+1H

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 in an explosion after a few hours.

Polyethylene oxide, or high-molecular-weight 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.

Alkaline catalysts, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), or sodium carbonate (Na2CO3), are used to prepare low-molecular-weight polyethylene glycol.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

See alsoEdit

ReferencesEdit

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External linksEdit

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