Ald-PEG-t-butyl ester is a type of polyethylene glycol (PEG) derivative that contains a tert-butyl ester functional group. This functional group is commonly used in pharmaceutical research and development because it can protect reactive functional groups from undesired reactions and improve the solubility of hydrophobic drugs. Additionally, the Ald-PEG-t-butyl ester can be used as a linker to connect drug molecules and targeting ligands, enabling the development of targeted drug delivery systems.