Polyethylene glycol (PEG) is asynthetic, hydrophilic, biocompatible polymer that has a wide range of uses in PEGylating,surface conjugation, nanoparticle coating, and crosslinking for hydrogels, etc.PEGs are made by polymerizing ethylene oxide via a ring-opening reaction toproduce a wide range of molecular weights and molecular weight distributions(polydispersity).