Vinylsulfone-PEG-vinylsulfone (VS-PEG-VS) is a thiol reactive homobifunctional PEG for sulfhydryl pegylation at high pH. Homobifunctional PEG derivatives have numerous applications as crosslinkers for PEGylation of proteins and peptides, nanoparticle and surface modifications. Conjugation with homobifunctional PEGs ensures an increased drug load compared to pegylation with linear PEGs.