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Polyethylene glycols, commonly abbreviated as PEGs, are a family of polyether compounds based on repeating ethylene oxide units (-O-CH2-CH2-). They are typically described by their average molecular weight (for example PEG 400 or PEG 3350). Most PEGs have hydroxyl end groups, giving them diol character, although end-group functionalization (such as methoxy-PEG) is also common.

Synthesis and structure: PEGs are produced by the polymerization of ethylene oxide, often initiated by water or a diol and carried out with catalysts. The resulting polymer chain length determines the molecular weight and physical form, ranging from low-molecular-weight liquids to high-molecular-weight waxy solids. The ether linkages impart high water solubility and chemical stability under ordinary conditions.

Physical properties and forms: The properties of PEGs depend strongly on molecular weight. Low to moderate MW PEGs are clear liquids or viscous fluids, while higher MW variants are polymers with higher viscosity or solid consistency. PEGs are generally highly water-soluble and hygroscopic, with low volatility and a broad range of viscosities suitable for various applications. End-group chemistry allows for attachment of functional groups or labeling.

Applications: PEGs are widely used as pharmaceutical excipients, solvents, plasticizers, lubricants, and humectants. They serve as carriers and stabilizers in formulations, as laxatives (notably at higher MWs), and as solubility enhancers and stabilizers in drug delivery. PEGylation, the covalent attachment of PEG chains to proteins or therapeutics, is a key strategy to increase solubility and circulation time. They are also used in cosmetics, personal care products, and industrial processes.

Safety and regulation: PEGs are generally regarded as safe for many uses, with low systemic toxicity when properly manufactured and purified. In some contexts, impurities such as residual ethylene oxide or 1,4-dioxane require control. Usage and regulatory status vary by application and jurisdiction.