Polyethylene glycol (PEG) is a synthetic ethylene oxide polymer with a repetitive structure of (O-CH2-CH2)n. In the 1970s Dr. Frank Davis reported the modification of a new recombinant protein with PEG with the goal of enhancing pharmacokinetics. The process of covalent coupling of PEG to another molecule including proteins, peptides, antibodies, and aptamers became known as PEGylation.