Propargyl-PEG9-amine is widely used in bioconjugation and click chemistry applications due to its terminal alkyne group, which allows for efficient and selective reactions with azide-functionalized molecules. It is particularly valuable in the development of drug delivery systems, where it facilitates the attachment of therapeutic agents to polyethylene glycol (PEG) chains, enhancing solubility, stability, and bioavailability. Additionally, it is employed in the functionalization of surfaces, nanoparticles, and biomaterials for targeted drug delivery and diagnostic imaging. Its role in protein and peptide modification further supports its use in biotechnological research and the creation of novel biomolecules. The PEG spacer provides flexibility and reduces steric hindrance, making it a versatile tool in synthetic and medicinal chemistry.