Propargyl-PEG4-bromide (CAS 1308299-09-3) is a polyethylene glycol (PEG) derivative containing an alkyne group (-C≡CH) and a bromine atom (-Br), with the molecular formula C₁₁H₁₉BrO₄ and a molecular weight of 295.17. Its structure consists of a PEG4 chain linking the propargyl group and the bromine atom, combining hydrophilicity and reactivity. Production typically involves a two-step process: first introducing the propargyl group into the PEG chain via acetylenation, then incorporating the bromine atom through bromination, which must be carried out under anhydrous and oxygen-free conditions to avoid side reactions. This reagent is widely used in copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions as a PROTAC linker or an irreversible ADC linker for targeted protein degradation and antibody-drug conjugate synthesis, holding significant value in biomedical research and drug development.