Heptaethylene glycol monomethyl ether is a linear poly(ethylene glycol) (PEG) derivative with a methoxy group at one terminus and a hydroxyl group at the other. It is a clear, colorless to pale yellow viscous liquid, soluble in water and many organic solvents. Its structure is defined by the formula CH3O-(CH2CH2O)7-H. This compound is primarily utilized as a surface functionalization agent and a building block for creating hydrophilic, biocompatible interfaces. Its long, flexible PEG chain imparts excellent antifouling properties, making it valuable for modifying surfaces to resist protein adsorption and cell adhesion. It is widely used in the preparation of functionalized nanoparticles, bioconjugates, and in the development of hydrogels and drug delivery systems where stealth properties and water solubility are crucial. As a versatile bifunctional PEG derivative, it serves as a key intermediate in organic synthesis and materials science. The reactive hydroxyl group allows for further conjugation with various molecules, enabling the synthesis of complex architectures like heterobifunctional crosslinkers, polymer initiators, and non-ionic surfactants.