m-PEG-Succinimidyl Amido Succinate (mPEG-SAS), MW 5K is a kind of MPEG-NHS ester reagent. SAS has a longer hydrolytic half-life and is therefore more stable in aqueous buffers than many other types of NHS esters.
AxisPharm offers 5000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.