FORMATION OF POLYION COMPLEX MICELLES IN AN AQUEOUS MILIEU FROM A PAIR OF OPPOSITELY-CHARGED BLOCK-COPOLYMERS WITH POLY(ETHYLENE GLYCOL) SEGMENTS

Stable and monodispersive polyion complex micelles were prepared in an aqueous milieu through electrostatic interaction between a pair of oppositely-charged block copolymers with poly(ethylene glycol) segments: poly(ethylene glycol)-poly(L-lysine) block copolymer (PEG-P(Lys)) and poly(ethylene glycol)-poly(alpha,beta-aspartic acid) block copolymer (PEG-P(Asp)). It was confirmed from photon correlation spectroscopy (dynamic light scattering) that the scaled average characteristic line width (Gamma/K-2) was independent of the magnitude of the scattering vector (K-2), and the diffusion coefficient (D-T) kept constant regardless of the concentration, indicating that the polyion complex micelles were spherical particles without any secondary aggregates. Further, polydispersity indexes (mu(2)/Gamma(2)) were always less than 0.1 in the range of the measured concentration (1-10 mg/mL). The hydrodynamic radius at infinite dilution of polyion complex micelles was then determined to be 15.2 nm by using the Stokes-Einstein equation. The unimodal size distribution with d(w)/d(n) of 1.07 was confirmed from the correlation function profile by the histogram analysis. The size of polyion complex micelles was unchanged even after a 1-month storing, suggesting that the polyion complex micelles are in thermodynamic equilibrium. Viscosity measurement as well as laser-Doppler electrophoresis provided evidence of the stoichiometry of the polyion complex micelles formation. These polyion complex micelles have potential utility as vehicles for charged compounds, i.e., proteins and nucleic acids, in the field of drug delivery.