  We experimentally measure the osmotic pressures of linear polymers and
three-, four-, and eight-arm star polymers in a good solvent via membrane
osmometry. These results reveal that the osmotic equations of state in the star
polymer solutions are universally described by the same scaling function that
describes linear polymer solutions. This universality is achieved by canceling
increasing overlap concentrations and decreasing osmotic pressure, owing to the
increased arm number. We further clarify the molar mass and arm number
dependencies of the gyration radius and interpenetration factor, ensuring
universality in star polymer solutions.
