Solubilization of hydrophobic compounds by micellar solutions of hydrophobically modified polyelectrolytes

Solubilization of pyrene and steroid hormones into aqueous solutions of an associative polymer, poly(ethylene oxide)-b-poly(propylene oxide)-b-(poly(ethylene oxide))-g-poly(acrylic acid) (Pluronic-PAA), has been studied. A dramatic increase of solubilization is observed upon formation of micelles above the critical micellization temperature (cmt). The equilibrium partition coefficients of the probes between micelles and water (K-m/w) above the cmt strongly correlate with the probe's octanol/water partition coefficient (K-o/w). The K-m/w is increased with the ionization degree of the poly(acrylic acid) (PAA) segments. Preferential solubilization of the increasingly hydrophobic compounds into the Pluronic-PAA is dominated by the entropic effect. Comparison of the fraction of the probe located in the hydrophobic cores of the micellar aggregates for pyrene and estradiol illustrates the degree of chemical specificity of the Pluronic-PAA micellar aggregates, which is due to the hydrophobicity of the probe.