ИСТИНА

Self-assembly of amphiphilic diblock copolymers polyisobutylene-block-poly(sodium methacrylate) containing 20 monomer units in polyisobutylene block and 100, 280, or 425 monomer units in poly(sodium methacrylate) (PMANa) block was examined in alkaline media by means of fluorescence technique with a use of pyrene as a polarity probe. For all the copolymers, the increase in their concentration above the certain value (cmc) was found to result in the formation of macromolecular micelles. The values of cmc were found to be about 1E-6 mole/L (cmc is given as the concentration of macromolecules), they being nearly independent of the length of PMANa block of the copolymers and ionic strength of the surrpunding medium. The hydrodynamic characteristics of such copolymer assemblies were determined by means of analytical ultracentrifugation and dynamic light scattering. The images obtained with transmission electron microscopy provided an evidence for a virtually spherical shape of the macromolecular micelles. The interaction between the copolymer micelles and a strong cationic polyelectrolyte poly(N-ethyl-4-vinylpyridinium bromide) with DPw = 500 in alkaline media was examined by means of turbidimetry, fluorescence spectroscopy (pyrene was used as a fluorescence probe), analytical ultracentrifugation, and dynamic light scattering. In mixtures containing charges of the polymeric components in non-equivalent ratios Z=[+]/[-] lower than the certain critical value Z<Z*<1, the formation of particles of water-soluble non-stoichiometric interpolyelectrolyte complexes considerably enriched by carboxylate groups of the anionic copolymers compared to pyridinium groups of the cationic polyelectrolyte was observed. The dependences of Z* on the concentration of low molecular weight salt (NaCl) were obtained for all the copolymers as well as for a reference anionic homopolyelectrolyte PMANa. Whereas for the homopolyelectrolyte the increase in the salt concentration is accompanied by a drastic decrease in the values of Z*, this tendency was either completely absent or only slightly visible for the copolymers. A particle of the formed interpolyelectrolyte complexes was suggested to be a peculiar micelle containing a two-component hydrophobic nucleus formed by a polyisobutylene core surrounded by a layer of coupled appositely charged polyelectrolyte fragments and an ionic corona formed by fragments of PMANa blocks not involved in interpolyelectrolyte interaction. At [NaCl] > 0.45 M, the interaction between the copolymer micelles and the cationic polyelectrolyte was found to be completely suppressed due to screening effect of small ions.