Poly(tert-butyl acrylate)-block-poly(2-vinylpyridine), PBA-b-PVP, was prepared by living anionic polymerization. Polymolecular spherical micelles with compact hydrophobic PEA cores and protonated PVP shells in acid water were prepared by a dialysis from organic-aqueous mixtures and are stable if the pH is less than pH 4.8. The stretching of the PVP blocks in shells depends on pH and ionic strength of the solution and decreases significantly in a narrow pH region below 4.8. Small hydrophobic molecules, such as benzene, may be solubilized into micellar core swelling the core and releasing the segmental mobility of core-forming blocks. Two fluorimetric techniques for determination of pyrene partitioning between micelles and the aqueous phase were used. The first method is based on measurements of the ratio of intensities of the first and third vibrational bands, I-1/I-3, in the emission spectra of pyrene solubilized in a micellar solution as a function of micellar concentration. The second method is based on the quenching of fluorescence from solubilized pyrene by thallium salts. The two experimental techniques yield close values of the apparent partition coefficient, K-app = 1.3 x 10(5) and 1.1 x 10(5), respectively.