Azido-PEG4-THP is a PEG-based PROTAC linker used for synthesizing PROTAC molecules. It functions as a click chemistry reagent, featuring an Azide group capable of engaging in a copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with molecules containing Alkyne groups. Additionally, it can undergo a strain-promoted azide-alkyne cycloaddition (SPAAC) with molecules that have DBCO or BCN groups.