Used as a PEG-based protecting group reagent in organic synthesis, particularly in peptide and pharmaceutical manufacturing. The tert-butyl ester functionality allows for selective protection of carboxylic acids, while the long PEG chain enhances solubility in aqueous and organic media, improving reaction efficiency and purification. Commonly employed in solid-phase synthesis and prodrug design due to its stability under basic conditions and easy deprotection under mild acidic conditions. Also utilized in bioconjugation processes where water solubility and biocompatibility are required.