ИСТИНА

The interaction of star-shaped poly(acrylic acid) ((PAA)x, x = 5, 8, and 21, DPn(arm) = 100) with a strong linear cationic polyelectrolyte, poly-N-ethyl-4-vinylpyridinium bromide (P4VP*EtBr, DPw = 600, 3000), in aqueous neutral and alkaline media was examined (pH 7, 9; [NaCl] < 0.3 M). This interaction was shown to result in the formation of water-soluble interpolyelectrolyte complexes (IPECs) if the basemole ratio Z of the aqueous mixtures the oppositely charged polymeric components, Z = [N+] / [COO- + COOH], does not exceed a certain maximum value Z* (Z* < 1), that is, when (PAA)x is present in the system in a certain excess compared to P4VP*EtBr. The values of Z* were observed to decrease with decreasing x as well as with increasing ionic strength of the surrounding solution, the former effect being more pronounced at higher salt concentrations. Sedimentation coefficients and hydrodynamic radii of the formed complex species were found to be either independent of Z (x = 5 and 8) or only weakly dependent on Z (x = 21), thus strongly suggesting that such particles are of characteristic (constant) stoichiometry which appears to be close to Z*. The sizes of the complex species based on (PAA)x with the small numbers of arms (x = 5 and 8) were shown to be considerably larger than those determined for the corresponding original polyelectrolyte stars, clearly indicating that polycation-induced assembly of (PAA)x leading to the formation of aggregates containing several polyelectrolyte stars takes place. At the same time, the size of the complex species resulting from the interaction of (PAA)21 with P4VP*EtBr was found to be decisively determined by degree of polymerization of the cationic polyelectrolyte: hydrodynamic radius of complex particles containing the shorter polycation is close to that determined for (PAA)21 whereas the formation of aggregates containing several polyelectrolyte stars is observed when (PAA)21 interacts with the longer polycation. At [NaCl] > 0.3 M, the interaction between (PAA)x and P4VP*EtBr was found to be suppressed because of the screening effect of small ions.