Characterization of Complex Branched Polymers by Multidetector Thermal Field-Flow Fractionation.

Size exclusion chromatography (SEC) for the molar mass analysis of polymers is of limited use for the analysis of branched polymers due to the co-elution of linear and branched molecules with similar hydrodynamic sizes but different molar masses. Thermal field-flow fractionation (ThFFF) in combination with multiple detection methods is a versatile alternative to SEC due to the fact that fractionation is not based entirely on molecular size but the interplay of thermal and translational diffusion that depend on molecular topology and molecular size. Multidetector ThFFF is used to investigate the correlation of branching and molar mass by determining polymer conformations from Mark-Houwink plots and the degrees of branching using functionality plots. The suitability of this approach is demonstrated for a set of 3-, 4-, and 6-arm star polystyrenes as well as a more complex hyperbranched polybutadiene-polystyrene copolymer. It is shown that ThFFF is a powerful tool for the analysis of the radius of gyration and the hydrodynamic radius when coupled online to static light scattering, viscometry, and dynamic light scattering. Shape factors are evaluated as influenced by branching where narrow dispersed star polystyrenes are used as model systems for the analysis of the more complex hyperbranched polybutadiene-polystyrene copolymer.