The synthesis and characterization of semiconductor quantum dots (QDs) with mixed polystyrene/poly(methyl methacrylate) (PS/PMMA) polymer brush stabilizing layers are described. Synthesis involves micellization of a PS-b-PAA-b-PMMA triblock copolymer, followed by growth of cadmium sulfide (CdS) QDs in the ionic cores. These environmentally responsive hybrid nanoparticles are studied in various solvents with different polarities (acetone, THF, chloroform, and toluene). Static and dynamic light scattering results indicate conformational changes in the mixed brush structure in response to different solvent polarities which allow the "smart" nanoparticles to maintain colloidal stability; UV-vis and photoluminescence spectra demonstrate that QD sizes and optical properties are independent of the solvent medium due to protection by the block copolymer. Long-term stability of QD size distributions in most investigated solvents is demonstrated for periods of up to 6 months. 2D H-1 NOESY experiments indicate that PS and PMMA chains are statistically distributed around the QDs within the mixed brush layer. It is also shown that the mixed brush QDs can be dispersed in both PS and PMMA homopolymers due to their environmentally responsive mixed brush layers.