Used in bioconjugation and drug delivery systems due to its bifunctional PEG structure with a disulfide linker. The disulfide bond is cleavable under reducing conditions, making it ideal for designing responsive carriers that release payloads inside cells, particularly in the cytoplasm where glutathione levels are high. Commonly employed to link polyethylene glycol (PEG) chains to proteins, peptides, or nanoparticles, enhancing solubility, stability, and circulation time while allowing controlled release. Also utilized in the synthesis of PEGylated reagents for research and therapeutic applications where reversible conjugation is required.