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

The association and surface properties of three oxyethylene/oxyphenylethyle ne (ES) diblock copolymers in aqueous solution have been studied. Copolymer s E50S3.5, E50S5.1, and E51S6.5 were synthesized and characterized by gel p ermeation chromatography and C-13 NMR spectroscopy. Surface tensiometry was used to determine critical micelle concentrations (cmc) at several tempera tures, 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 E51S6.5), which is c onsistent with the high hydrophobicity of oxyphenylethylene block. Dynamic and static light scattering were used to characterize the micelles in dilut e solution, yielding micellar association number, hydrodynamic and thermody namic radius, and the related thermodynamic expansion factor. At higher con centrations, solution of copolymers E50S5.1 and E51S6.5 formed hard isotrop ic gels.