What is polyethylene glycol (PEG)?
PEG is the common abbreviation for polyethylene glycol – or, more properly, poly(ethylene glycol) – which refers to a chemical compound composed of repeating ethylene glycol units.

Purified PEG is most commonly available commercially as mixtures of different oligomer sizes in broadly or narrowly defined molecular weight (MW) ranges. For example, "PEG 600" typically denotes a preparation that includes a mixture of oligomers having an average MW of 600. Likewise, "PEG 10000" denotes a mixture of PEG molecules (n = 195 to 265) having an average MW of 10,000g/mol.

Properties of PEG
Poly (ethylene glycol) has several chemical properties that make it especially useful in various biological, chemical and pharmaceutical settings:

Non-toxic and non-immunogenic – can be added to media and attached to surfaces and conjugated to molecules without interfering with cellular functions or target immunogenicities
Hydrophilic (aqueous-soluble) – attachment to proteins and other biomolecules decreases aggregation and increases solubility
Highly flexible – provides for surface treatment or bioconjugation without steric hindrance