Release of hydrophobic compounds from micellar solutions of hydrophobically modified polyelectrolytes

The kinetics of release of the hydrophobic probes, pyrene and estradiol, fr om micellar aggregates of poly(ethylene oxide)-b-poly(propylene oxide)-b-(p oly(ethylene oxide))-g-poly(acrylic acid) (Pluronic-PAA), have been studied . Release of the probes is bimodal with a fast and a slow component. Diffus ion coefficients of 10(-15)-10(-14) cm(2)/s characterize the slow mode of d iffusion from the core of the micellar aggregates. The core of the aggregat es consists mainly of poly(propylene oxide) (PPO) and possesses different p roperties from those of bulk PPO, with there being a higher activation ener gy for diffusion of pyrene and dramatic changes in the polarity of the micr oenvironment of the probe. The temperature-dependent fine structure of the pyrene spectra (I-3/I-1) in Pluronic-PAA above the critical micellization t emperature (cmt) can be explained by a redistribution of pyrene from hydrop hobic PPO domains into micelles.