SS-PEG-SS (PEG-bis-Succinimidyl Succinate), MW 3.4K, has two succinimidyl (NHS) ester groups and is highly reactive with amines at physiological pH, resulting in stable amide linkages.
AxisPharm offers 5000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.