Molar mass fractionation in aqueous two-phase polymer solutions of dextran and poly(ethylene glycol)

• Tie lines for ATPS of dextran and PEG were constructed using a method based on GPC measurements of the separated phases.
• Molar mass fractionation in ATPS leads to the redistribution of dextran of different chain lengths between the two phases.
• The separation parameters show a crossover from mean field to Ising model behavior, as the critical point is approached.

Dextran and poly(ethylene glycol) (PEG) in phase separated aqueous two-phase systems (ATPSs) of these two polymers, with a broad molar mass distribution for dextran and a narrow molar mass distribution for PEG, were separated and quantified by gel permeation chromatography (GPC). Tie lines constructed by GPC method are in excellent agreement with those established by the previously reported approach based on density measurements of the phases. The fractionation of dextran during phase separation of ATPS leads to the redistribution of dextran of different chain lengths between the two phases. The degree of fractionation for dextran decays exponentially as a function of chain length. The average separation parameters, for both dextran and PEG, show a crossover from mean field behavior to Ising model behavior, as the critical point is approached.