Polymer Fractionation in Aqueous Two‐Phase Polymer Systems

Abstract

We consider the effects of the addition of poly(ethylene glycol) (PEG) of different molecular weights to aqueous two-phase system of PEG 8000 and dextran 500. The first purpose of this study was to determine the molecular weight partitioning of the polymers themselves so that, for example, aqueous two-phase separations using affinity ligands can be improved. The second purpose was to examine whether this molecular weight partitioning could be predicted by using solution thermodynamic models so that it would be possible to optimize affinity partitioning without extensive laboratory work. Experimentally, we find that, by increasing the PEG concentration of any molecular weight in the feed, the high molecular weight PEG concentration in the dextran-rich phase is reduced. This observation can be used to reduce the loss of expensive ligated PEG used in affinity partitioning. Further, there is generally good agreement between our experimental data and the predictions of a solution thermodynamic model.

Effect of temperature on the phase equilibrium of aqueous two‐phase polymer systems

“…In the following calculations, PEG 8000 ( b = 1.1) was assumed to be monodisperse due to its narrow molecular weight distribution, and DEX (b=2.75) is represented by three pseudocomponents chosen as described above. Representing a polydisperse polymer by as few as three quadrature-chosen pseudocomponents is sufficient to allow accurate predictions of phase boundaries (Kang and Sandler, 1988;Hartounian and Sandler, 1991). Using this method, the optimum pseudocom- The Gibbs free energy minimization was done as follows.…”

Partitioning of Vancomycin Using Poly(ethy1ene glycol)‐Coupled Ligands in Aqueous Two‐Phase Systems

“…We had expected the partition coefficient of PEG-CI-D-Ala-D-Aa to be slightly lower than MPEG-CI-D-Ala-D -A a because of the difference in their molecular weights. There is a significant degree of polymer fractionation in the two-phase system, which distributes the higher molecular weight PEG in the top phase and the lower molecular weight PEG more evenly between the two phases (Hartounian and Sandler, 1991). However, these two partition coefficients are too close to make any judgement since we found deviations of up to 7% in the measurements of the partition coefficients.…”

“…The two-phase system consists of polydisperse polymers constituting these phases. The average molecular weight of PEG in the dextran system is much less than that in the PEG phase (Hartounian and Sandler, 1991;Lee and Sandler, 1990). In other words, the higher molecular weight PEG would be predominantly in the top phase, and by coupling the affinity ligand on a higher molecular weight PEG, the partition coefficient of the ligand can be dramatically increased.…”

Autobiography of Stanley I. Sandler

“…Helmut had considerable industrial experience; spending time at his institute introduced me to a collection of experimental equipment for measuring vapor-liquid phase behavior at both low and high pressures. When I returned to Delaware, I initiated an experimental thermodynamics program that continued for many years using what I had learned and then expanded to include liquid-liquid equilibrium; infinite dilution properties ; and, most recently with my colleagues at Delaware, the separation of biologics and pharmaceuticals (73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83)(84)(85).…”