There has been increasing interest in the synthesis of star-branched polymers due to their unusual flow and viscosity properties compared to linear analogs. Starbranched polymers are constructed with several ‘arms’ radiating from a central core, either by preparing the individual arms and attaching them to a central molecule - the ‘arms first’ approach - or by growing the polymer arms from a central core - the ‘core first’ approach. Many commercial polymers can be constructed with a star-branched morphology relatively easily, but their characterization is still a challenge to the analytical chemist. Gel permeation chromatography (GPC) employing a concentration detector (typically a refractive index detector) combined with a viscometer can be used to measure not only the molecular weight of the materials but also to investigate the star-branched structure. The 390-MDS is ideal for this type of application since it was specifically designed to extract additional information from polymers by GPC. A series of PS star-branched polymers was analyzed, which had been synthesized by a ‘core first’ approach giving theoretical 5-, 14- and 21-arm structures.