Comb-shaped polystyrenes with UV-labeled side chains were synthesized and analyzed by SEC with on-line light scattering and viscometry detection. The introduction of the UV label allows for a model-independent determination of the number of grafts within each SEC slice and therefore the calculation of the expected contraction factors, g = < R-g,br(2)>/< R-g,R-lin> and g' = [eta](br)'[eta](lin). Using molecular weight sensitive detectors, the contraction factors were determined experimentally and compared to the expected ones. It was found that the experimentally determined g values are larger than the ones calculated on the basis of the Gaussian chain assumption. Therefore, the calculation of the number of branches based on theoretically expected contraction factors is not feasible. Attempts to include corrections for excluded-volume effects failed. For the exponent epsilon of the relationship g' = g(epsilon) a value close to epsilon = 1 was found, in contradiction with the expectations from the Flory-Fox and Zimm-Kilb relations. It was observed that the intrinsic viscosities of the combs are close to the intrinsic viscosities of the parent backbone polymer itself, allowing to use this empirical relationship for the determination of the amounts of grafts present in the polymer.