This linear homofunctional PEG derivative is used as a crosslinking agent. The free thiol groups react readily with maleinimides or halides as in iodoacetates or bromoacetates to form stable thioether bonds. Stable bonds are also formed with transition metal surfaces like gold, silver etc. Reaction with other free thiols leads to S-S disulfide bonds which can be cleaved by reducing agents. PEG thiols may also be conjugated by thiol-ene chemistry.