Abstract
We probe the dynamic structure factor of multiarm star polymer solutions in good solvent above the overlap concentration with photon correlation spectroscopy and NMR. With the aid of a mean-field theoretical approach, which accounts for the interplay between the topologically enhanced osmotic pressure and the arm entropic stretching, we identify three mechanisms for relaxing the concentration and density fluctuations: cooperative diffusion, self-diffusion and structural relaxation. These model spherical brushes exhibit a behavior intermediate between polymers and colloids.