Azido-PEG4-azide is widely used in bioconjugation and click chemistry applications due to its dual azide functional groups and PEG spacer. It serves as a versatile linker in the synthesis of complex molecules, enabling the attachment of biomolecules, polymers, or nanoparticles. Its PEG chain enhances solubility and reduces immunogenicity, making it suitable for drug delivery systems and biopharmaceutical development. Additionally, it is employed in the preparation of hydrogels, surface modifications, and the functionalization of materials for biomedical research. Its ability to participate in copper-catalyzed azide-alkyne cycloaddition (CuAAC) reactions makes it a valuable tool for creating stable and specific covalent bonds in various chemical and biological contexts.