Used as a hydrophilic linker in pharmaceutical and bioconjugation applications, particularly in the development of antibody-drug conjugates (ADCs) and peptide conjugates. Its extended PEG chain enhances solubility and improves pharmacokinetic properties of conjugated molecules. The terminal tert-butyl ester protects the carboxylic acid during synthesis and can be easily deprotected under mild acidic conditions to release the active acid form for further coupling. Ideal for creating stable, water-soluble constructs in drug delivery systems and diagnostic reagents.