Liquid Chromatography of Polymers under Limiting Conditions of Desorption, 3

Abstract

Liquid chromatography under limiting conditions of desorption (LC LCD) enables the elution of adsorbing macromolecules independent of their size in solution. In this way, polymer species with different adsorptivities can be separated without mutual interference. It is shown on systems of bare silica gel, a tetrahydrofuran/toluene-mixed eluent and poly(methyl methacrylate)s (PMMA) that LC LCD produces narrow, focused peaks with retention volumes independent of not only polymer molar mass but also, to a large extent, the concentration and volume of the injected sample. Sample capacity of LC LCD is very high, and sample volume can reach as much as 80% of the column pore volume. Reduced sample dilution or even its re-concentration within the column is important for two-dimensional separations. Changes in temperature as large as 40 °C only slightly affected retention volumes of the LC LCD-eluted PMMA. Consequently, the LC LCD method is rather robust and user-friendly. A practical application of LC LCD for the separation of model polymer blends has been demonstrated. Polystyrene and PMMA of similar molar masses were easily separated in less than four minutes using a small LC LCD column of low efficiency. The LC LCD fractions were successively transported into an on-line SEC column either directly or after storage in the LC LCD column. The SEC system was equipped with a refractive index detector and a multi-angle light scattering (MALS) detector. The MALS detector proved a good reproducibility of the molar masses for polymer blend components determined with a combination of LC LCD and SEC. Storage of the fractions within the LC LCD column even for several hours exhibited only a negligible effect on the determined molar mass averages.