t-Boc-N-amido-PEG-amine (tBOC-NH-PEG-Amine) is an amine-modified PEG polymer with a t-Boc protecting group. Can be used for direct coupling to succinimidyl or PFP esters via amide bond formation. The t-Boc can be removed with strong acid to yield the free amine. Applications are particularly suitable for the development of antibody drug conjugates (ADCs).