Heterografted macromolecular brushes are highly grafted macromolecules with two different side chains attached to a backbone. When endowed with an amphiphilic character, these can serve as unique stabilizers of biphasic systems and solute carriers and yield interesting self-assembled structures. Herein, we report on the solution structure of amphiphilic double-brush copolymers with short backbones i.e., comparable to the length of the side-chains in a selective solvent for one of the grafted blocks. As determined by small-angle neutron scattering measurements, poly(ethylene glycol)/poly(D,L-lactide) double brushes adopt a cylindrical structure with highly extended backbones in DMSO. In contrast, brushes undergo intermolecular self-assembly into spherical nanoparticles in water, with aggregation numbers that vary inversely with backbone degree of polymerization. While considerably less susceptible to intermolecular association than linear diblocks of similar hydrophobic and hydrophilic block lengths, the inability of the PEG component to maintain their unimolecular form results in well-defined spherical nanoparticles with very low aggregation numbers (3 < N-agg < 10) which could potentially lead to interesting compartmentalized nanomaterials.