Nanocs Pentafluorophenyl PEG (PEG-PFP) derivatives, including methoxy PEG-PFP and other heterofunctional PFP-PEG derivatives, are amine reactive PEGs that can be used to modify biomolecules, particles and other material surfaces with available amine groups. Compared to succinimidyl NHS PEGs, PFP-PEGs have higher reactivity and they can react with both primary and secondary amines. In addition, PFP-PEG is more stable under normal storage conditions.