Polymeric Lipid Nanosphere Consisting of Water-Soluble Poly(2-methacryloyloxyethyl phosphorylcholine-co-n-butyl methacrylate)

As water-soluble amphiphilic polymers with the phospholipid polar group (PMB), 2-methacryloyloxyethyl phosphorylcholine(MPC) copolymerized with n-butyl methacrylate (BMA), were synthesized. The properties of the MPC polymers in water were investigated by surface tension measurement, 1H NMR and fluorescence spectroscopy, and light scattering measurement. The solubility of the MPC polymers in water depended on MPC unit composition and molecular weight. The surface tension of the aqueous solution depended on the MPC unit composition in the PMB. In the case of poly(MPC), the surface tension did not change as in the case of water at polymer concentrations from 10−5 gd L−1 to 10−1 gd L−1. However, introduction of the BMA unit in the MPC polymer induced decrease in surface tension considerably above 10−4 g dL−1 polymer concentration. This result clearly shows that the PMB forms aggregates in water. According to fluorescence spectroscopy results, the PMB aggregate formed a hydrophobic domain in water and the polarity of the hydrophobic domain was the same as that of n-butanol. From the NMR spectra of the PMB in D2O at various temperatures, the phosphorylcholine groups were located at the surface of aggregate below 60°C. The light scattering measurement revealed that the size of the PMB aggregate in water was 23 nm. A hydrophobic fluorescence probe was entrapped in the hydrophobic inside of the PMB aggregate. The PMB aggregate thus quite likely has potential application as a novel drug carrier, to maintain hydrophobic drugs inside polymer aggregates stably.