ИСТИНА

The micellization of ionic amphiphilic diblock copolymers, polyisobutylene-block-poly(methacrylic acid), in aqueous media was examined. The molar values of the critical micellization concentration measured by means of fluorescence spectroscopy with a use of pyrene as a polarity probe were found to be around 1E-6 M, these values being nearly independent of the degree of polymerization of the poly(methacrylic acid) block (DPn = 100 ÷ 425) as well as of pH (pH = 6 ÷ 9) and ionic strength ( ≤ 0.5 M NaCl) in the system. The hydrodynamic characteristics of the copolymer micelles determined by means of analytical ultracentrifugation and dynamic light scattering were shown to be sensitive to the variations of pH and ionic strength of the solution: a decrease of pH or an increase of ionic strength resulted in a decrease of hydrodynamic radii of such macromolecular assemblies and an increase of their sedimentation coefficients. It was demonstrated that the formed copolymer micelles mixed at pH > 6.5 with strong cationic polyelectrolytes, poly(N-ethyl-4-vinylpyridinium bromide) or 2,5-ionene bromide, at charge ratios Z = [+]/[-] not exceeding a certain critical value Z*, Z* < 1, form water-soluble interpolyelectrolyte complexes. The results obtained by means of analytical ultracentrifugation, dynamic light scattering, and fluorescence spectroscopy allow us to consider their particles as peculiar onion-like micelles, each containing a two-component hydrophobic nucleus and a hydrophilic corona. The nucleus consists of a polyisobutylene core surrounded by a shell assembled from the fragments of poly(methacrylic acid) blocks coupled with cationic macromolecules. The corona is formed by excess fragments of the poly(methacrylic acid) blocks not involved in the interpolyelectrolyte complexation. At relatively high ionic strength in the system, the micellar complex species were found to dissociate to the individual copolymer micelles and cationic macromolecules because of the screening effect of small ions.