Polyethylene glycol (PEG) and polyethylene oxide (PEO) are polymers having an identical structure except for chain length and end groups, and are the most commercially important polyethers. Polyethylene glycol refers to an oligomer or polymer with low molecular weight while polyethylene oxide is used for higher molecular weights. PEG generally is a liquid while PEO is a low-melting solid. Both are prepared by polymerization of ethylene oxide. While they find use in different applications and have different physical properties (i.e. more...
viscosity) due to chain length effects, their chemical properties are nearly identical.
Polyethylene glycol has the following structure:
Pegylation is the act of adding a PEG structure to another larger molecule, for example, a protein (which is then referred to as pegylated).
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 surfactants.
Polyethylene glycol is non-toxic and is used in a variety of products. It is the basis of a number of laxatives (e.g. macrogol-containing products such as Movicol® and polyethylene glycol 3350, or MiraLax®). It is the basis of many skin creams, as cetomacrogol, and sexual lubricants, frequently combined with glycerin.
Polyethylene glycol with added electrolytes is used for bowel preparation and drug overdoses. It is sold under the brandnames GoLYTELY and Colyte.
When attached to various protein medications, PEG allows a slow release of the carried protein. This makes for a longer acting medicinal effect and/or reduces toxicity, and allows longer dosing intervals. Examples include PEG-interferon alpha (used to treat hepatitis C) and PEG-filgrastim (Neulasta®).
It has been shown that PEG can improve healing of spinal injuries in dogs .
PEG is also used in liquid body armor and tattoos to monitor diabetes. Functional groups of PEG give polyurethane elastomers their "rubberiness", for applications such as foams (foam rubber) and fibers (spandex). Its backbone structure is analogous to that of silicone, another elastomer.
Since PEG is a flexible polymer, it can be used to create very high osmotic pressures (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.
PEO can serve as the separator and electrolyte solvent in lithium polymer cells. Its low 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.
Polyethylene glycol is also commonly used as a polar stationary phase for gas chromatography.
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