The unique hydration state of poly(2-methacryloyloxyethyl phosphorylcholine)

2-Methacryloyloxyethyl phosphorylcholine (MPC) is methacrylate bearing a phosphorylcholine group in the side chain. The phosphorylcholine group generates several unique properties arising from its zwitterionic structure, consisting of a phosphate anion and a trimethylammonium cation. Despite these charged groups, the total electrical charge of the species is zero because of the formation of an inner salt. The polymerization of MPC proceeds both conventional and living radical polymerizations. And, using these method, the corresponding polymer can be obtained efficiently. The product, poly(MPC), is soluble in aqueous media, even if the ionic strength of the solution is high, such as in the presence of 5.0 mol/L NaCl. The polymer does not show any surface active properties, even when the polymer concentration is greater than 1.0 g/dL. Hydration of poly(MPC) mainly occurs by hydrophobic hydration of the three methyl groups in the trimethylammonium group. Thus, this hydration induces an increase in a clathrate cage structure of surrounding water molecules, i.e. an ice-like water state is formed. Because of this unique hydration, poly(MPC) cannot make strong interactions with proteins and cells. Some biomedical applications have used poly(MPC) as a protein and solid-surface modification agents.