Azido-PEG4-acyl chloride is a PROTAC linker that falls under the PEG category, utilized in the synthesis of PROTAC molecules. As a click chemistry reagent, it contains an Azide group, allowing it to undergo copper-catalyzed azide-alkyne cycloaddition reactions (CuAAC) with molecules bearing an Alkyne group. Additionally, it can partake in strain-promoted azide-alkyne cycloaddition reactions (SPAAC) with molecules containing DBCO or BCN groups.