"PEG", "PEO", and "POE" refer to an oligomer or polymer of ethylene oxide. The three names are chemically synonymous, but historically "PEG" is preferred in the biomedical field, whereas "PEO" is more prevalent in the field of polymer chemistry. Because different applications require different polymer chain lengths, "PEG" has tended to refer to oligomers and polymers with a molecular mass below 20,000g/mol, "PEO" to polymers with a molecular mass above 20,000g/mol, and "POE" to a polymer of any molecular mass. PEGs are prepared by polymerization of ethylene oxide and are commercially available over a wide range of molecular weights from 300g/mol to 10,000,000g/mol.