Polyethylene glycol
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Polyethylene_glycol_chemical_structure.png
Polyethylene glycol (PEG) and polyethylene oxide (PEO) are polymers have an identical structure except for chain length and end groups, and are the most commercially important polyether. Polyethylene glycol refers to the polymer with molecular weight less than 50,000 (a condensation polymer made from ethylene glycol), while polyethylene oxide is used for higher molecular weights (an addition polymer). While they find use in different applications and have different physical properties (i.e. viscosity) due to chain length effects, their chemical properties are nearly identical.
Polyethylene glycol has the following structure:
- H-(CH2-CH2-O)n-H
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.
Uses
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®). As cetomacrogol it is the basis of many skin creams.
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 [1] (http://seattlepi.nwsource.com/health/202292_spinal04.html).
PEG is also used in liquid body armor [2] (http://www.military.com/NewsContent/0,13319,usa3_042104.00.html) and tattoos to monitor diabetes[3] (http://news.bbc.co.uk/2/hi/health/2225404.stm). Functional groups of PEG give polyurethane elastomers their "rubberiness", for applications such as foams and fibers.
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. [4] (http://aqueous.labs.brocku.ca/osfile.html)
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 cary greater energy for their weight than other lithium ion battery technologies.