Thermodynamic properties of diblock copolymers of ethylene oxide and styrene oxide in aqueous solution

Apparent molal volumes and adiabatic compressibilities of aqueous solutions of block copolymers E45S10, S15E63, S17E65, and S20E67 (E = oxyethylene, S = oxyphenylethylene, and the subscripts denote block lengths) have been determined by density and ultrasound velocity measurements. Values of the critical micelle concentrations (cmc's) were impossible to evaluate by ultrasound velocity because of their low concentration motivated by the hydrophobicity of the oxyphenylethylene block. Copolymer E45S10 was studied in the temperature range of 20-50 degreesC. Its cmc and the enthalpy of demicellization have been also determined by isothermal titration calorimetry at 30 degreesC. The low enthalpy values that are obtained are attributed to the hydrophobicity of the S block being tightly coiled in the molecular state in water. The thermodynamic aggregate properties of copolymers S15E63, S17E65, and S20E67 were determined from density and calorimetry at 30 degreesC.