Onion-type micelles from polystyrene-block-poly(2-vinylpyridine) and poly(2-vinylpyridine)-block-poly(ethylene oxide)

Polystyrene-block-poly(2-vinylpyridine) (PS-b-PVP) was synthesized by anionic polymerization. Micellization of PS-b-PVP was accomplished by dissolving the polymer in a 45:50:5 volume ratio methanol:dioxane:water mixture followed by a stepwise dialysis into a 0.1 M HCl solution. The hydrophobic PS blocks form the core of the micelles, and the protonated PVPH+ forms the outer shell. Addition of poly(2-vinylpyridine)-block-poly(ethylene oxide) (PVP-b-PEO) and titration to a pH above 10 causes a coprecipitation of the PVP blocks of both copolymers, forming three-layered micelles that we refer to as "onion" micelles. The micellar structures were investigated by static and dynamic light scattering and transmission electron microscopy. The weight ratio of PVP-b-PEO to PS-b-PVP was varied during the onion micelle preparation to study the fraction of PVP-b-PEO that is adsorbed on the PS-b-PVP "core micelle". The stability with respect to dilution of the micelles formed from PS-b-PVP and of the onion micelles was studied.