Supramolecular assemblies formed by self-associating block copolymers have raised considerable interest in the scientific literature. [1] In most cases, amphiphilic diblock copolymers are dissolved in a solvent selective for one constituent, which results in spherical micelles that consist of a core formed by the insoluble blocks surrounded by a shell of the solvated blocks. Although ABC triblock copolymers self-organize into a wide variety of supramolecular structures in the bulk, [1] their association in selective solvents has scarcely been studied. ªThree-layerº micelles were reported in water, [2] although other micelle structures can be formed in organic solvents, as demonstrated by the so-called ªJanusº micelles, [3] which consist of a cross-linked polybutadiene core and a corona with a ªnorthernº polystyrene and ªsouthernº poly(methyl methacrylate) hemisphere. These Janus micelles have to be distinguished from three-layer micelles, because their structure is generated in the bulk and persists in solution.
Herein we report on the formation of aqueous three-layer micelles from a polystyrene-block-poly(2-vinyl pyridine)block-poly(ethylene oxide) triblock (PS-b-P2VP-b-PEO), these micelles will be referred to as core ± shell ± corona (CSC) micelles. The molecular weight of each block is 20 000 for PS, 14 000 for P2VP, and 26 000 for PEO. CSC micelles consisting of a PS core, an intermediate P2VP layer, and a PEO corona are expected to be formed. Because the watersolubility of the central P2VP block depends on the degree of ionization, [4] the CSC micelles should be pH sensitive. Structurally they are reminiscent of the so-called ªonionº micelles prepared by mixing an aqueous micellar solution of PS-b-P2VP diblock with P2VP-b-PEO chains dissolved in water. [5] At pH b 10, the P2VP blocks of the two copolymers coprecipitate, and three-layer onion micelles, that consist of a PS core, a P2VP shell, and a PEO corona are formed. The effect of pH on the onion micelles is dramatically different from that on the CSC micelles, the onion micelles disintegrate into the two constituent diblocks as the pH is decreased, which is not the case for their CSC counterparts which remain intact. Moreover, the structural features of the CSC micelles can be better controlled than those of the onion micelles. 0.71073 ), q-2q scan, T 298 K, 10 115 measured reflections, 9702 independent reflections (R int 0.0339) included in the refinement. Lorentzian, polarization, and y-scan absorption corrections were applied, m 2.568 mm À1 , [D/s] max 0.046, 734 parameters refined, R1 0.0477 (for 8333 reflections with I b 2s(I)), wR2 0.1231 (on j F 2 j ). Max./min. residual peaks in the final difference map 0.794/ À 0.599 e À3 . Crystals of 1 and 2 were mounted in capillaries filled with drops of the mother liquor. The structures were solved by direct methods with SHELXS 86 and refined by full-matrix least-squares techniques on F 2 using SHELXL 93. For both structures, almost all non-hydrogen atoms were refined anisotropically; the MeCN solvate and two lattice H 2 O molecules of 2 were refined isotropically with occupation factors fixed at 10.76 and 10.50, respectively. All hydrogen atoms in 1 were introduced at calculated positions as riding on bonded atoms. Hydrogen atoms of the methyl groups of the acetate ligands and those of C9, C23, C24, C28, C29, C30, and C31 in 2 were introduced at calculated positions as riding on bonded atoms, the remaining hydrogen atoms were located by difference map calculations and refined isotropically; no hydrogen atoms for the H 2 O and MeCN solvate molecules were included in the refinement. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-147434 and CCDC-147435. Copies of the data can be obtained free of charge on application to CCDC,