Polyethylene oxide (PEO), also known as polyethylene glycol (PEG), is a water-soluble polymer. PEO is a synthetic, non-toxic, and biocompatible polymer that is widely used in various applications, including pharmaceuticals, cosmetics, and food additives. It is a linear or branched polymer of ethylene oxide, and its solubility in water is attributed to the presence of hydrophilic ether groups along the polymer chain. The hydroxyl end groups of PEO also contribute to its water solubility. The solubility of PEO in water depends on its molecular weight, with lower molecular weight PEO being more water-soluble than higher molecular weight PEO.