Stearic acid-PEG-CH2CO2H is a heterobifunctional poly-PEG with 18 carbon aliphatic chains and carboxyl groups, and because of this it forms micelles in water, a drug delivery system that can improve drug solubility and improve Drug formulation and bioavailability. Carboxyl groups can react with amines in the presence of activators such as HATU/EDC to form stable amide bonds.