Comparison of Temperature Effects on the Salting Out of Poly(ethylene glycol) versus Poly(ethylene oxide)-Poly(propylene oxide) Random Copolymer

In common with many poly(ethylene glycol)s (PEGs), a poly(ethylene oxide)-poly(propylene oxide) random copolymer (EO-PO, with EO/PO = 1:1.3) of molecular weight 3320 g.mol(-1), known as Sunbright-3320 (SB-3320), can be salted out of aqueous solution using kosmotropic salts such as (NH4)(2)SO4 to form aqueous biphasic systems (ABSs) comprising upper polymer-rich and lower salt-rich aqueous phases. The effects of temperature on these liquid/liquid ABSs and related solid/liquid resin-based systems, where one end of the polymer has been covalently attached to a solid support, have been studied. Distribution ratios of (NH4TcO4)-Tc-99 were determined radiometrically at various polymer and salt concentrations and temperatures. SB-3320-grafted poly(styrene) resins exhibit opposite effects of variable-temperature partioning compared to the SB-3320-based ABS. However, the results are complicated because of the conformational changes that are possible for the SB-3320 polymer. Enthalpy and entropy changes were found to be temperature-dependent. The differences observed between the distribution of (TcO4-)-Tc-99 in EO-PO-based systems versus PEG-based systems can be attributed to the lower cloud point temperatures and probable conformational changes for the EO-PO systems.