N-(Tos-PEG4)-N-bis(PEG4-t-butyl ester) is a branched PEG linker with a Tos-PEG4 branch and two PEG4-t-butyl ester groups attached to a central nitrogen. The tosyl group is a very good leaving group for nucleophilic substitution reactions. The t-butyl ester can be removed under acidic conditions. The hydrophilic PEG linker increases the water solubility of the compound. Branched PEG linkers can have more conjugations.