Association of Hydrophobically End-Capped Poly(ethylene oxide). 2. Phase Diagrams

The solubility of hydrophobically end-capped poly(ethylene oxide) (PEO) was studied in pure water and in the presence of salts as a function of temperature. Behaviors of α and α,ω-modified PEO of various molecular weights and different numbers of carbons in the aliphatic end groups were compared. Experimental results show that phase separation in aqueous solutions of PEO with one end group occurs at a higher temperature than that for unmodified PEO of the same molecular weight. On the contrary, the solubility of difunctionalized PEO (with two aliphatic end groups) is strongly depressed in comparison to that for the unmodified samples. This loss of solubility increases upon increasing temperature and salinity. All the presented results are consistent with a theoretical model assuming an equilibrium structure of “starlike” or “flowerlike” micelles for mono- and difunctionalized PEO, respectively. To explain the observed behavior, one must take into account both the short-range interactions between the EO monomers, which vary with temperature and the salinity, and bridging attraction between flowerlike micelles for difunctionalized PEO.