Propargyl-PEG3-phosphonic acid diethyl ester is a PEG-based PROTAC linker can be used in the synthesis of PROTACs[1]. Propargyl-PEG3-phosphonic acid diethyl ester is a click chemistry reagent, it contains an Alkyne group and can undergo copper-catalyzed azide-alkyne cycloaddition (CuAAc) with molecules containing Azide groups.