Effects of Molecular-Weight Distribution on SEC-MALS Measurements

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  • SEC-MALS測定における分子量分布の影響について
  • SEC-MALS ソクテイ ニ オケル ブンシリョウ ブンプ ノ エイキョウ ニ ツイテ

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Abstract

The weight-average molecular weight Mw and the z-average mean-square radius of gyration ⟨S2⟩z were measured using a size-exclusion chromatography system equipped with a multi-angle light scattering (MALS) detector and a refractive index (RI) detector as functions of the elution time t for three standard polystyrene (PS) samples (Mw = 3.55 × 105, 7.06 × 105, 1.09 × 106) and a their mixture in toluene. The RI signal and Mw and ⟨S2⟩z values as functions of t for the standard PS’s were expressed by calculated values assuming that the molecular weight distribution and the band broadening effect are described by Gaussian functions. However, the RI elution curve for the mixture was not expressed by a sum of the elution curves for the standard PS’s. This was considered to come from the effect that low-molecular-weight components fill up the pores in the gel particles of the column. By taking this effect into consideration, the RI elution curve and Mw and ⟨S2⟩z values for the mixture were successfully expressed by calculated curves. The ⟨S2⟩z values for the mixture deviated from the known ⟨S2⟩z-Mw relation for PS in toluene. The deviation became serious with increasing Mz/Mw, which was found to have a maximum when described as a function of t, where Mz means the z-average molecular weight. The peak time of Mz/Mw was later than the peak time of the RI curve, showing that very small amount of high-molecular-weight components effectively increases Mz/Mw.

Journal

  • KOBUNSHI RONBUNSHU

    KOBUNSHI RONBUNSHU 69 (7), 387-391, 2012

    The Society of Polymer Science, Japan

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