ИСТИНА

The interaction of ionic amphiphilic diblock copolymers polyisobutylene-block-poly(methacrylic acid) (PIB(X)-b-PMAA(Y); X = DPn(PIB) and Y = DPn(PMAA); X = 20, Y = 100; X = 20, Y = 425; X = 75, Y = 615; X = 75, Y = 1610) with the double hydrophilic (ionic/non-ionic) diblock copolymers poly(N-methyl-2-vinylpyridinium methylsulfate)-block-poly(ethylene oxide) (P2VPq(A)-b-PEO(B); A = DPn(P2VPq) and B = DPn(PEO); A = 40, B = 210; A = 40, B = 450, A = 70, B = 450) in aqueous media at pH 7 and 0.1 M NaCl was examined. Aqueous mixtures of PIB(X)-b-PMAA(Y) and P2VPq(A)-b-PEO(B) were found to remain homogeneous for any value of the ratio between amounts of the ionic groups of the polymeric components Z, Z = [N+]/[COO- + COOH] (the base-molar concentrations of the corresponding polymeric components are given in the brackets), which is in striking contrast to the reference system, that ts, the aqueous mixtures of PIB(X)-b-PMAA(Y) and poly(N-methyl-2-vinylpyridinium methylsulfate) (P2VPq, DPn = 30 ÷ 4400 that undergoes phase separation when Z exceeds the certain threshold value (Z* = 0.4 ÷ 0.5). Dynamic light scattering carried out for stoichiometric (Z = 1) homogeneous mixtures of PIB(X)-b-PMAA(Y) and P2VPq(A)-b-PEO(B) provides evidence on monomodal distribution of apparent hydrodynamic radius Rh(app) of the formed macromolecular co-assemblies which is distinctly less than apparent hydrodynamic radius of the corresponding micelles of PIB(X)-b-PMAA(Y). Further analysis of such homogeneous mixtures by means of analytical ultracentrifugation provides evidence that the macromolecular co-assemblies can be considered as particles of water-soluble interpolyelectrolyte complex (IPEC) resulting from the interaction of the PIB(X)-b-PMAA(Y) micelles with P2VPq(A)-b-PEO(B). Molecular weight of the complex species formed in stoichiometric (Z = 1) mixture of PIB(20)-b-PMAA(100) and P2VPq(70)-b-PEO(450) determined by means of static light scattering allows to calculate the aggregation number of the corresponding PIB(20)-b-PMAA(100) micelle incorporated into IPEC, which nearly coincides with the corresponding PIB(20)-b-PMAA(100) micelle incorporated into IPEC, which nearly coincides with the aggregation number previously measured for the corresponding PIB(20)-b-PMAA(100) micelle. This finding strongly suggests that the PIB(X)-b-PMAA(Y) micelles do not change their aggregation numbers upon interpolyelectrolyte complexation with P2VPq(A)-b-PEO(B) diblock copolymers. Altogether the obtained experimental results provide evidence that the formed macromolecular co-assemblies have compartmentalized "core-shell-corona" structure with a hydrophobic core assembled from PIB blocks of the corresponding PIB(X)-b-PMAA(Y) micelles, a rather hydrophobic shell assembled from the coupled oppositely charged polyelectrolyte fragments, and a hydrophilic corona built up from the non-ionic PEO blocks, providing solubility of the whole complex species in aqueous media. Direct visualization of complex particles formed in a mixture of PIB(20)-b-PMAA(100) and P2VPq(70)-b-PEO(450) at Z = 1 by cryogenic transmission electron microscopy shows clearly spherical objects with diameters of 20 ÷ 26 nm, which are reasonably attributed to the PIB core surrounded by the complex shell, while the PEO blocks forming the corona are not visible due to poor contrast, allowing evaluation of the radius of the combined core and shell in the complex species R(core + shell) = 10 ÷ 13 nm, which results in the thickness of the complex shell D(shell) = 6 ÷ 10 nm, as the radius of the PIB core of the micelle PIB(20)-b-PMAA(100) R(core) is 3 ÷ 4 nm. The thickness of the PEO corona D(corona) estimated as the difference between the hydrodynamic radius of the IPEC particles (Rh = 29 nm) and R(core + shell) is 16 ÷ 19 nm, which is about 15% ÷ 17% of the contour length of the PEO block (B = 450), thereby indicating a rather high degree of coiling of such blocks in the corona.