Effect of cosolvents and cosolutes upon aggregation transitions in aqueous solutions of the poloxamer F87 (Poloxamer p237): A high sensitivity differential scanning calorimetry study

The effects of a number of different cosolvents and cosolutes upon the micellization of the oxyethylene/oxypropylene/oxyethylene block copolymer F87 (P237; 70% oxyethylene and 30% oxypropylene) have been investigated using high-sensitivity differential scanning calorimetry (HSDSC). The calorimetric output has been analyzed using a model fitting procedure to obtain estimates for various thermodynamic parameters which characterize the micellization event as observed by HSDSC. These important parameters include Tn, the temperature at which the micellization process is half-completed, Delta H-cal, the calorimetric enthalpy for the process which is measured by integration of the calorimetric output; Delta(vH), the van't Hoff enthalpy; and n the aggregation number. From this data it has been possible to measure critical micelle concentrations (cmcs). The experimental investigations reveal that methanol, ethanol, urea, and formamide prevent the onset of micellization, while butanol and hydrazine favor micelle formation. Finally a thermodynamic model simulation is developed and presented which appears to be capable of explaining the major effects of methanol upon micellization.