Copolymers sensitive to temperature and pH in water and in water+oil mixtures: A DSC, ITC and volumetric study

Block copolymer micelles are receiving an increasing interest because of the variety of structures and the possibilities to tune them by changing external and internal parameters achieving the desired properties for a specific purpose. We have investigated the acid/base behavior, self-assembling and solubilization ability towards polar oils of star-like copolymers named Tetronics. They are composed of branched four-arms each one consisting of two blocks made of EO and PO units linked to the diethylenediamine group, which confers pH response ability. The copolymers T1107 and T90R4 were studied with a sequential and reverse architecture. The thermodynamics of the acid/base equilibrium was studied by ITC. The aggregation of T1107 in water was analyzed as functions of pH, composition and temperature. The enhanced oil solubilization in the aqueous T1107 aggregates was widely investigated highlighting the role of the oil structure, composition, temperature and pH. As a general result, the oil induces the copolymer aggregation and the solubilization power of micelles is tunable by changing the pH. Efforts have been devoted to model the calorimetric data in order to achieve the thermodynamic properties of the involved process. Finally, we showed that the Tetronic micelles are more promising than the conventional surfactants micelles because of the larger solubilization power and flexibility of the macromolecular system.