Ald-Ph-PEG4-bis-PEG3-N3, a 6-unit cleavable PEG ADC linker, is used in the preparation of antibody-drug conjugates (ADCs) [1]. It serves as a click chemistry reagent featuring an Azide group, allowing it to engage in a copper-catalyzed azide-alkyne cycloaddition reaction (CuAAc) with Alkyne-containing molecules. Additionally, it can participate in strain-promoted alkyne-azide cycloaddition (SPAAC) with molecules that contain DBCO or BCN groups.