Propargyl-PEG3-bromide (CAS No.: 203740-63-0) is a PEG-based molecule containing an alkyne group and a bromine atom, with the molecular formula C₉H₁₅BrO₃ and a molecular weight of 251.12. Its structure consists of a triethylene glycol (PEG3) chain linking the propargyl group and a bromine atom, combining hydrophilicity and reactivity. It is produced via the Williamson ether synthesis using propargyl alcohol and brominated triethylene glycol as raw materials. The etherification reaction occurs under basic conditions, followed by purification through column chromatography or recrystallization. This reagent serves as a PROTAC linker and a click chemistry tool, finding wide application in targeted protein degradation, biomolecular modification, and drug carrier design. It supports copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions and is a key intermediate in chemical biology and materials science.