Used in pharmaceutical and biotechnology applications as a hydrophilic linker or spacer in drug conjugates, particularly in antibody-drug conjugates (ADCs) and peptide modifications. Its long PEG chain enhances solubility and improves pharmacokinetic properties by reducing aggregation and increasing circulation time. The tert-butyl ester (tBu) group allows for mild deprotection to reveal a carboxylic acid, enabling further conjugation with amines or other functional groups. Commonly employed in solid-phase synthesis and bioconjugation strategies where controlled release or steric shielding is required. Also utilized in the development of PEGylated prodrugs and diagnostic agents due to its biocompatibility and stealth properties.