What is peg?Polyethylene glycol (peg full form) is chemically a polyether compound. Mostly it is formed by the addition of ethylene oxide to ethylene glycol or diethylene glycol. Therefore the common structure of Polyethylene glycol can be expressed as H−(O−CH2−CH2)n−OH. Polyethylene glycol structure forms a crystalline thermoplastic polyether that is practically water-soluble in applicable concentrations and exhibits very low immunogenicity, antigenicity and toxicity. Polyethylene glycol structure is a hydrophilic molecule, having high flexibility. The excellent aqueous solubility of Polyethylene glycol is due to the distance of the oxygens in the glycol structure that is similar with the distance of the hydrogens in the water molecule. This property is unique to Polyethylene glycols among all other aliphatic polyethers which are commonly not water-soluble.