4arm-PEG-SS (4arm-Succinimidyl Succinate-PEG), MW 10K is a cleavable PEG linker. There is a C2 hydrocarbon ester linkage between the PEG and the NHS ester. NHS is a good leaving group that can react with amine-containing moieties.
AxisPharm offers 5000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.