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(e thylene oxide))-g-poly(acrylic acid) (Pluronic-PAA), has been studied. A dr amatic increase of solubilization is observed upon formation of micelles ab ove the critical micellization temperature (cmt). The equilibrium partition coefficients of the probes between micelles and water (K-m/w) above the cm t 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(acryl ic acid) (PAA) segments. Preferential solubilization of the increasingly hy drophobic compounds into the Pluronic-PAA is dominated by the entropic effe ct. Comparison of the fraction of the probe located in the hydrophobic core s of the micellar aggregates for pyrene and estradiol illustrates the degre e of chemical specificity of the Pluronic-PAA micellar aggregates, which is due to the hydrophobicity of the probe.