The micellization of ionic amphiphilic diblock copolymers, polyisobutylene-block-poly(methacrylic acid) (PIB-b-PMAA), with a constant degree of polymerization of the non-ionic block ((DP) over bar (n) = 20) and various degrees of polymerization of the polyelectrolyte block ((DP) over bar (n) = 100-425) was examined in aqueous media by means of fluorescence spectroscopy using pyrene as a polarity probe. The molar values of the critical micellization concentration (cmc) were found to be around 2 x 10(-6) mol/l, being nearly independent of the length of the polyelectrolyte block as well as pH (in the range 6-9) and ionic strength (less than or equal to 0.5 M NaCl) while the specific cmc values varied from 20 to 100 mg/l. Small-angle neutron scattering (SANS) and dynamic light scattering (DLS) experiments provided evidence that aggregation numbers and hydrodynamic radii of the formed copolymer micelles are sensitive to variations of pH and ionic strength, indicating that these micelles might be 'dynamic' rather than 'frozen' ones. It was also shown by means of a combination of turbidimetry, analytical ultracentrifugation, fluorescence spectroscopy, SANS, and DLS that the formed copolymer micelles mixed with a strong cationic polyelectrolyte, poly(N-ethyl-4-vinylpyridinium bromide) at charge ratio Z = [+]/[-] not exceeding a certain critical value Z(M) < 1, generate peculiar water-soluble micellar complex onion-like species, each containing a two-phase hydrophobic nucleus and a hydrophilic corona. The nucleus consists of a PIB core and a shell assembled from the fragments of water-insoluble interpolyelectrolyte complex. The corona is formed by the excess fragments of poly(sodium methacrylate) blocks not involved in complexation with poly(N-ethyl-4-vinylpyridinium bromide). (C) 2004 Elsevier Ltd. All rights reserved.