Block copolymers (BCPs) can self-assemble in selective solvents to form morphologies based on their chemistries' and architectures. In this study, we investigate BCPs having both brush and linear segments in what is referred to as "toothbrush" architecture. Using anionic polymerization, we have synthesized a linear poly(styrene-block-isoprene) followed by growing poly(ethylene oxide) grafts from the isoprene block to form a brush segment. A combination of nonselective and selective solvents is used to drive the self-assembly of the toothbrush polymers. Analysis by dynamic light scattering and transmission electron microscopy show that the self-assembly is highly influenced by the density of grafts in the brush segment, with densely grafted polymers forming only spherical micelles and sparsely grafted brushes forming higher order structures including cylindrical micelles and vesicles. Additionally, calculations of micelle corona graft density and corona thickness indicate that the corona of the micelles formed by densely grafted polymers is composed of the entire brush segment while the corona of micelles formed by sparsely grafted polymers is composed solely of grafts. The results of this study will inform the design of BCP self-assembled morphologies through architecture control, enabling the design of polymer aggregates with programmed morphologies and sizes in aqueous solutions.