Entropically Driven Partitioning of Ethylene Oxide Oligomers and Polymers in Aqueous/Organic Biphasic Systems

Abstract

Partitioning of ethylene oxide oligomers and polymers (PEO) in biphasic systems of water and chloroform or dichloromethane favors transfer to the organic phase as the molecular weight increases. For systems containing chlorobenzene, partitioning into the aqueous phase is always predominant. Calorimetric determination of the enthalpies of transfer for PEO from aqueous to organic phases reveals an endothermic process for all of the systems investigated, which was ascribed to the replacement of a more energetically favored PEO solvation in water for that in the organic phase. These results indicate that spontaneous PEO transfer from water to an organic phase is driven by an entropy increase. The number of water molecules transferred to the organic phase with PEO was determined to be ca. 0.08 water molecules per EO unit, smaller than hydration numbers reported in aqueous solutions. All of these findings lead to a picture where PEO may be extracted from water to an organic phase as long as the solvation by the organic solvent is relatively strong as compared to water. The displacement of water causes an entropy increase, which drives the transfer process. Chloroform and dichloromethane are suitable solvents for PEO extraction probably because of their hydrogen bonddonating capability.

Interfacial properties of Pluronics and the interactions between Pluronics and cholesterol/DPPC mixed monolayers

“…Mpofu et al [32] have demonstrated that there was hydrogen bond force between ether oxygen (Lewis base) on the PEO chains and OH (Brønsted acid) group. Besides, Spitzer et al [33] have investigated the partitioning of PEO polymers between water phase and oil phase. The interaction between PEO polymers and the organic solvent was suggested to occur through hydrogen bond-donating capability of the solvent.…”

Interfacial Tension-Hindered Phase Transfer of Polystyrene-b-poly(ethylene oxide) Polymersomes from a Hydrophobic Ionic Liquid to Water

“…Presumably, the hydroxyl end group of PEG interacts with water molecules more favorably than with the IL and contributes to the phase transfer from the IL. 41 When one of the end groups is changed to a hydrophobic group, the contribution of the hydroxyl end groups for the phase transfer is diminished. This result implies that the hydrophobic nature of a molecule or an assembly is important in the phase transfer from IL to water.…”

Thermodynamics of the partitioning of poly(propylene oxide) between aqueous and chlorinated organic phases compared to poly(ethylene oxide) and other hydrophilic polymers

“…-partitioning of PEO between aqueous and organic (CHCl 3 and CH 2 Cl 2 ) phases depends on its molar mass, being it almost quantitatively transferred to the organic phases at higher molar masses, resulting from the decrease in end group contributions; 5,6 -PEO is not extracted to chlorobenzene phases, which has been ascribed to the lack of hydrogen bond donating capacity of this organic solvent; 6 -PEO partitioning is endothermic and, hence, must be entropically driven; 6 -a significant amount of water molecules are released from their role of solvating PEO as it is transferred to the organic phases, and this release is ascribed as being the origin of the entropy increase. 6 Some of these findings were more recently confirmed by the report of an investigation on the partitioning of PEO between aqueous and fluorinated organic phases. 7 The study reported here presents new data on the partitioning of PEO, but also extends the same systematic investigation to the partitioning of poly(propylene oxide), PPO, producing thermodynamic data which are discussed in comparison to those for PEO.…”