Noncovalently connected polymeric micelles in aqueous medium

Differing from the conventional micelles made of block or graft copolymers, in which the core and corona are connected by covalent bonding, the micelles reported in this paper are composed of a polymer pair and the core and corona are connected by hydrogen bonding. Poly(styrene-co-methacrylic acid) (SMAA) and poly(vinylpyrrolidone) (PVPo) self-assembled into spherical micelles with hydrodynamic radii around 100 nm in aqueous medium. These stable micelles are composed of the core of collapsed SMAA chains and the corona of solvated PVPo chains. The hydrogen bonding between methacrylic acid and PV-Po units and the difference in the solubility in water between SMAA and PV-Po are the main factors responsible for the micelle formation. Using dynamic light scattering, it was found that the hydrodynamic radius of the micelles significantly increases with increasing initial concentrations of both SMAA and PVPo. The micelle size dose not depend on the MAA content (3.55-13.1 mol %) in SMAA monotonically, which can be rationalized by the coexistence of different stabilization mechanisms. Transmission electronic microscopy (TEM) was used to observe morphologies of the micelles. The core-shell structure of the micelles became visualized only when adequate staining of the TEM specimens was employed.