Dendrimers are highly branched polymers prepared by alternating addition of monomers to a multifunctional core, resulting in a layered, treelike structure. Grafting monofunctional linear polymers (arms) onto dendrimer endgroups results in hybrid copolymers with starlike architecture. These dendrimer-star polymers are model branched macromolecules with controllable size, number of branches,and miscibility.Current work in Polymers Division involves testing dendrimer-star polymers as sub-micrometer probe molecules. To facilitate detection of the stars on a sub-micrometer length scale, we label the stars with molecular-level markers: fluorescent organic dyes or inorganic nanoparticles (gold, cadmium sulfide). Thespatial distribution of labeled stars in polymer blends may be probed by fluorescence microscopy or transmission electron microscopy. The stars may also be useful as size-tunable probes for characterization of mass transport through membranes and porous structures.