PEG12-Tos, a polyethylene glycol monotosylate derivative, is primarily used as a reactive intermediate in organic synthesis for PEGylation processes. It enables the conjugation of PEG chains to molecules via nucleophilic substitution of the tosylate group, enhancing water solubility, bioavailability, and stability of poorly soluble drugs in pharmaceuticals. In bioconjugation, it links PEG to proteins, peptides, or other biomolecules for drug delivery systems and biomaterials. Additionally, it finds applications in cosmetics for formulating hydrating and emulsifying agents, and in complex chemical syntheses to modify molecular properties.