N-(Aminooxy-PEG3)-N-bis(PEG4-t-butyl ester) is a branched PEG linker with aminooxy and t-butyl ester moieties. The aminooxy group can react with aldehyde to form an oxime bond. If a reductant is used, it will form a hydroxylamine linkage. The t-butyl ester group can be removed under acidic conditions. The hydrophilic PEG linkers increase the water solubility of the compound.