S-Acetyl-PEG4-t-butyl ester is widely used in bioconjugation and chemical synthesis. It serves as a versatile linker in the development of antibody-drug conjugates (ADCs), enabling the attachment of cytotoxic drugs to antibodies for targeted cancer therapy. The compound is also employed in the modification of peptides, proteins, and other biomolecules, enhancing their solubility, stability, and bioavailability. Its PEG spacer improves pharmacokinetic properties, while the acetyl and t-butyl ester groups allow for controlled release and protection during synthesis. Additionally, it is utilized in the preparation of prodrugs, where the t-butyl ester can be cleaved under specific conditions to release active therapeutic agents. This makes it a valuable tool in drug delivery systems and pharmaceutical research.