Bromo-PEG3-MS is a PEG derivative containing bromine and methanesulfonic acid (Ms) groups. Its structure consists of a triethylene glycol (PEG3) backbone modified with a bromine atom at one end and a methanesulfonate group at the other. The production process employs chemical synthesis, using precise control of reaction conditions to achieve dual functional group modification through bromination and methanesulfonate esterification, ensuring a product purity of ≥95%. Leveraging the high leaving group character of bromine and the primary alcohol protecting function of the methanesulfonate group, this compound is widely used in PROTAC molecule synthesis, drug delivery system development, and as an organic synthesis intermediate. It serves as a key tool for linking bioactive molecules with targeted carriers.