Azido-PEG9-Boc is a PEG-based PROTAC linker that can be used in the synthesis of PROTACs[1]. Azido-PEG9-Boc is a click chemistry reagent, it contains an Azide group and can undergo copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing Alkyne groups. Strain-promoted alkyne-azide cycloaddition (SPAAC) can also occur with molecules containing DBCO or BCN groups.