ИСТИНА

Self-assembly of amphiphilic diblock copolymers polyisobutylene-block-poly(sodium methacrylate) cotaining 20 monomer units in polyisobutylene (PIB) 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 tested, the increase in their concentrations above the cetain value (cmc) was found to result in the formation of macromolecular micelles. The values of cmc were found to be about 1E-06 mole/L (cmc is given as the concentration of macromolecules), they being nearly independent of the length of the ionic block. The hydrodynamic characteristics of such copolymer assemblies (sedimentation coefficient, hydrodynamic radius) 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-vinyl pyridinium bromide) with DPw = 500 in alkaline media was examined. A possibility for the formation of particles of water-soluble interpolyelectrolyte complex (IPEC) considerably enriched by carboxylate groups of the anionic copolymers compared to pyridinium groups of the cationic polyelectrolyte was demonstrated for all the copolymers tested. The dependences of the critical content Zcr = [+]cr/[-] of the cationic polyelectrolyte (the molar concentrations of ionic groups of the polyelectrolytes in their mixtures are given in the brackets) below which particles of water-soluble IPEC are formed in the mixtures of the oppositely charfed polymeric components but above which these mixtures loose their homogenity and become phase separated on the concentration of NaCl were obtained for the copolymers as well as for a reference anionic homopolyelectrolyte sodium polymethacrylate (PMANa). For the copolymers with the shorter lengths of the ionic block, the values of Zcr were found either to increase (PIB20-block-PMANa100) or to be nearly independent (PIB20-block-PMANa280) of the salt concentration. These trends are quite different from that observed in the case of PMANa for which the increase in the concentration of NaCl is accompanied by a drastic decrease in the values of Zcr. For the copolymer with the longest length of the ionic block (PIB20-block-PMANa425), the salt dependence of Zcr resembled that observed for PMANa up to 0.2 M NaCl while at higher salt concentrations it seemed to demonstrate the same trend as for the other copolymers. At [NaCl] > 0.4 - 0.45 M, the formation of IPECs was detected neither for all the copolymers tested nor for PMANa because of the screening effect of small ions suppressing the interaction between the oppositely charged polymeric components. (B. P 15)