Association and surface properties of poly(ethylene oxide)-poly(styrene oxide) diblock copolymers in aqueous solution

The association and surface properties of three oxyethylene/oxyphenylethylene (ES) diblock copolymers in aqueous solution have been studied. Copolymers E(50)S(3.5), E(50)S(5.1), and E(51)S(6.5) were synthesized and characterized by gel permeation chromatography and (13)C NMR spectroscopy. Surface tensiometry was used to determine critical micelle concentrations (cmc) at several temperatures, and thereby values of the enthalpy of micellization (Delta(mic)H(0)). The values of Delta(mic)H(0) and Delta(mic)H(0) were found to be low (e.g., 0.03 g dm(-3) at 30 degrees C and 12 kJ mol(-1) for E(51)S(6.5)), which is consistent with the high hydrophobicity of oxyphenylethylene block. Dynamic and static light scattering were used to characterize the micelles in dilute solution, yielding micellar association number, hydrodynamic and thermodynamic radius, and the related thermodynamic expansion factor. At higher concentrations, solution of copolymers E(50)S(5.1) and E(51)S(6.5) formed hard isotropic gels.