| Abstract: | With the aid of polystyrenes with different polydispersity (M?w/M?n = 2,6 to 1,01) the effect of the charge, the γ-gradient, the interval Δgamma; between two fractions and the contact time on the discontinuous and continuous solution fractionation was tested. For the discontinuous fractionation of samples with broad distributions no effect was found on the integral distribution curve by the variation of these experimental conditions. For narrower distributions (M?w/M?n ≤ 1,5) however it is necessary to pay attention to following points: 1st the charge must be below 2mg/g sand, 2nd the γ-gradient must be specially accommodated to the conditions of solubility, 3rd the interval Δγ should be smaller than 0,002 and 4th the contact time should be at least two hours. With growing uniformity the charge has to be reduced further and the contact time has to be increased. Compared to the discontinuous solution fractionation the continuous fractionation produces insufficient results under equal experimental conditions. Even for broad distributions the charge and the y-gradient must be reduced for approaching the results of the discontinuous fractionation. Furthermore the elution chromatography shows no improvement compared to the simple continuous fractionation. All column methods — including the BAKER WILLIAMS fractionation — can be shown to be single stage processes. |
