DETERMINATION OF THE COMPOSITIONAL HETEROGENEITY OF POLYDISPERSE POLYMER SAMPLES BY THE COUPLING OF SIZE-EXCLUSION CHROMATOGRAPHY AND THERMAL FIELD-FLOW FRACTIONATION

An off-line coupling of size-exclusion chromatography (SEC) and therma l field-flow fractionation (ThFFF) was used successfully to cross-frac tionate copolymers and polymer blends. Various fractions of different molecular mass were obtained from polydisperse polymer samples by SEC. Because the molecular diffusion coefficients were known, the ThFFF an alysis of these fractions yielded directly thermal diffusion coefficie nts. As thermal diffusion is strongly affected by the chemical nature of the polymer, the chemical composition of polymer samples can be stu died as function of the molecular mass with this technique. This is il lustrated with the SEC-ThFFF cross-fractionation of a polystyrene samp le blended with a polybutadiene and a polytetrahydrofuran standard, an d of butadiene- and styrene-methylmethacrylate copolymers.