ИСТИНА

The interaction of star-shaped polyacrylic acid (PAA)N with the number of arms N = 5, 8, and 21 (DPn(arm) = 75) with the strong linear cationic polyelectrolyte, poly-N-ethyl-4-vinylpyridinium bromide P4VP*EtBr (DPw = 570), in aqueous media (pH 7, 0.05 M < [NaCl] < 0.3 M) was examined by means of turbidimetry and analytical ultracentrifugation. This interaction was shown to result in the formation of water-soluble interpolyelectrolyte complexes (IPECs) if the charge ratio Z in the system, Z = [+]/[-] (molar concentrations of the ionic groups of the corresponding polymeric components are given in the brackets), does not exceed a certain critical value of Z*, Z < Z* (Z* = 0.1 ÷ 0.4, depending on N and [NaCl]). In such IPECs, the star-shaped anionic polyelectrolyte whose ionic groups are incorporated in the complex particles in the escess appears to play a lyophilizing part, providing solubility of the whole complex particles in aqueous media, while the linear cationic polyelectrolyte functions as a "guest" component. The values of Z* were found to gradually decrease with the decreasing number of arms of the (PAA)N stars, this effect becoming more pronounced with the increasing concentration of NaCl. The analysis of the homogeneous mixtures of the oppositely charged polymeric components (tha is, at Z < Z*) by means of analytical ultracentrifugation provided evidence that all cationic macromolecules are bound to the (PAA)N stars. The sedimentation coefficient S of the complex particles were shown to increase with the rising N, being within several Svedbergs (e.g., at 0.1 M NaCl and Z = 0.2, S = 3.8, 4.3, and 6.8 Sv, respectively). At the same time, the values of S appear to be nearly independent of Z (for the (PAA)N stars with N = 5 and 8) or weakly dependent on Z (for the (PAA)N star with N = 210, thus strongly suggesting the formation of the complex particles of the characteristic composition which appears to be close to Z*. For the (PAA)N stars with N = 5 and 8, this finding implies that the particles of IPECs can incorporate several stars, that is, the polycation-induced assembly of the star-shaped (PAA)N takes place. The electrostatic interaction between the (PAA)N and P4VP*EtBr was found to be completely suppressed at rather high ionic strength of the surrouding medium ([NaCl] > 0.4 M) due to the screening effect of small ions. The dissociation of IPECs based on the (PAA)N stars (regardless of the value of N) to the individual polymeric components was observed virtually at the same concentrations of NaCl, this process proceeded via a gradual release of the cationic macromolecules from the complex particles upon the increasing ionic strength of the surrounding media.