Change of molecular weight distribution of polymers by adsorption from binary and ternary solutions

Abstract

The change in molecular weight distribution (MWD) for polymers of different thermodynamic flexibility and polarity (cellulose triacetate, CTA and cis-1.4-poly(butadien), PB) as a result of adsorption from binary and ternary solutions have been studied by the liquid chromatography method (SEC). These changes depend on the ratio of adsorbent weight to volume of solution ( A/ V), on concentration of the polymer solution and on the ratio of components in the mixture. It was shown that for nonporous silica from the binary solutions the fractions of rigid CTA chains with lower molecular weight are adsorbed preferentially at the lowest values of A/ V in the investigated concentration region ( C* ≤ C < C*), where C* is critical concentration of overlapping of macromolecular coils. The fractions of CTA with medium molecular weight begin to adsorb with increase of A/ V. Contrary to CTA, increase of concentration of adsorbent leads to inversion in adsorption of fractions with higher molecular weight of flexible nonpolar PB, which are adsorbed at the lowest silica ( A/ V) ratio at C < C*. With increase of solution concentration up to C ≥ C* the fractions of PB with lower molecular weight are adsorbed. Insignificant adsorption of the fractions with lower molecular weight of PB is observed during the preferential adsorption of its fractions with higher molecular weight with increase of A/ V. By adsorption from the CTA/PB mixtures the fractions of stiff-chain polar CTA with lower molecular weight are adsorbed preferentially and the fractions with higher molecular weight of flexible-chain nonpolar PB are adsorbed insignificantly. With increase of A/ V the adsorption of fractions with the lower and the medium molecular of CTA is increased and adsorption of fractions with higher molecular weight of PB is decreased. From the ternary solutions at all component ratios the fractions with lower molecular weight of CTA are adsorbed preferentially. The fractions with higher molecular weight of PB are adsorbed preferentially when the PB concentration in the mixture is equal or exceed the concentration of CTA. When concentration of PB is lower than concentration of CTA the fractions with lower molecular weight of PB are adsorbed preferentially.