4arm-PEG-SS (4arm-Succinimidyl Succinate-PEG), MW 5K is a multi-arm PEG derivative with a succinimidyl NHS active ester group at each end of the 4 arms of the pentaerythritol core.
AxisPharm offers 5000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.