The structure of many common types of polymer may be modified by either postpolymerization reaction or by the use of modified monomers, producing materials with new and novel properties. Understanding and assessing the effect of these modified structures on the behavior of polymers in various applications is crucial to developing novel uses for such materials. Polystyrene is one of the most commonly seen polymers, used primarily for the manufacture of packing materials. Modified forms of polystyrene may be produced by the use of novel styrene monomers. Gel permeation chromatography (GPC) is a well-known technique for assessing the molecular weight distribution of polymers, a property that influences many physical characteristics. Importantly, increasing the sophistication of the GPC experiment by the use of additional detectors allows the structure and solution properties of polymers to be assessed, of interest when studying the affect of structural modifications on a polymer. Triple detection employing a light scattering detector and a viscometer in combination with a refractive index detector may be used to determine accurate molecular weights for polymers for which narrow standards are not available, and to assess their solvation properties. This application note describes the analysis of a sample of polystyrene and a modified polybromostyrene material by triple detection.