Poly(styrene)-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO) ABC triblock copolymers commonly form core-shell-corona (CSC) micelles in water. These micelles consist of a PS spherical core, a P2VP shell, and a PEO corona. However, when the micelles are formed in the presence of a solvent selective for the PS block (benzene), the micellar morphology exhibits a sphere-to-rod transition, as result of the increased volume fraction of the core-forming blocks. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) confirm that a PS rod-like core is surrounded by a P2VP shell and an external PEO corona. Nevertheless, the rod-like micelles coexist with spherical micelles that should be thermodynamically less stable, because of a higher stretching of the PS chains in the core. The P2VP chains are also in a stretched conformation, whatever the pH. The P2VP shell has been used as nanoreactor for the production of gold nanoparticles.