The formation of multicompartment micelles featuring a “spheres on sphere” core morphology in acetone as a selective solvent is presented. The polymers investigated are ABC triblock terpolymers, polybutadiene-b-poly(2-vinyl pyridine)-b-poly(tert-butyl methacrylate) (BVT), which were synthesized via living sequential anionic polymerization in THF. Two polymers with different block lengths of the methacrylate moiety were studied with respect to the formation of multicompartmental aggregates. The micelles were analyzed by static and dynamic light scattering as well as by transmission electron microscopy. Cross-linking of the polybutadiene compartment could be accomplished via two different methods, “cold vulcanization” and with photopolymerization after the addition of a multifunctional acrylate. In both cases, the multicompartmental character of the micellar core is fully preserved, and the micelles could be transformed into core-stabilized nanoparticles. The successful cross-linking of the polybutadiene core is indicated by ¹H NMR and by the transfer of the aggregates into nonselective solvents such as THF or dioxane.