Polyethylene glycol (PEG) and polyethylene oxide are polymers of ethylene oxide. Polyethylene glycol refers to the polymer with molecular weight less than 50,000, while polyethylene oxide is used for higher molecular weights.

Polyethylene glycol has the following structure:

-(CH2-CH2-O)_n-

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).

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)