m-PEG5-sulfonic acid contains a methoxy and a sulfonic acid end group. While sulfonic acids can undergo esterification, halogenation and replacement reactions, the hydrophilic PEG linker together with methoxy moity greatly increase the water solubility of the resulting compound.
AxisPharm offers 5000+ PEG Linkers with high purity. Different kinds of PEG Reagents may be available by custom synthesis.
