ИСТИНА

This contribution considers interpolyelectrolyte complexes (IPECs) based on star-shaped polyelectrolytes, such complexes being formed (A) in aqueous media upon a direct mixing of the aqueous solutions of poly(acrylic acid) stars, (PAA)N, with the number of arms N = 5, 8, and 21 (DPn(arm) = 100) and poly(N-ethyl-4-vinylpyridinium bromide), PVPEt-Br, (DPw = 600, 3000) and (B) in organic media of low polarity (chloroform) upon a direct mixing of organic (chloroform) solutions of star-shaped poly(hexadecyltrimethylammonium acrylate), PA-HDTMA, and poly(N-ethyl-4-vinylpyridinium dodecylsulfate), PVPEt-DDS, which were prepared via a replacement of protons of (PAA)N or bromide counterions of PVPEt-Br by the said surfactant counterions. (A) Formation and Properties of IPECs Based on (PAA)N in Aqueous Media On addition of the aqueous solution of PVPEt-Br to the aqueous solution of (PAA)N (that is, (PAA)N is present in the mixtures in an excess) at pH 7, the phase separation is observed only if the base-molar ratio of the polymeric components Z (Z = [PVPEt-Br]/[(PAA)N], the base-molar concentrations of the corresponding polymeric components being given in the brackets) exceeds a certain threshold value ZM, that is, at Z > ZM, the values of ZM being decisively determined by the number of arms of (PAA)N and ionic strength of the surrounding solution. The analysis of the homogeneous aqueous mixtures of (PAA)N and PVPEt-Br by means of dynamic light scattering provides evidence that they contain two types of the IPEC species, the sizes of the small complex species being comparable to the sizes of the corresponding pure (PAA)N (or exceeds those not more than by a factor of ca 2) while the sizes of the large complex species considerably exceeding the sizes of the corresponding pure (PAA)N. The fraction of the large IPEC particles appears to increase with the decreasing number of arms of (PAA)N, with the rising content of the cationic polyelectrolyte in the aqueous mixtures of (PAA)N and PVPEt-Br, and with increasing ionic strength of the surrounding solution. Each of the small IPEC species is thought to contain only one chain of the cationic polyelectrolyte and the corresponding minimum number of (PAA)N needed to provide solubility of the whole complex particle in aqueous media while each of the large IPEC species is hypothesized to be a stable on the colloidal level aggregate which comprises plenty of chains of both polymeric components. (B) Formation and Properties of IPECs Based on (PAA)N in Chloroform On addition of the chloroform solution of PVPEt-DDS to the chloroform solution of (PA-HDTMA)N (that is, (PA-HDTMA)N is present in the mixtures in an excess), the pronounced phase separation is observed even upon incorporation of first portions of the titrant, thus undoubtedly evidencing the formation of insoluble IPECs, viz., (PA)N - PVPEt. Turbidity reaches the maximum at nearly equivalent base-molar concentrations of the both polymeric components. After ca 10 - 15 min the formed turbid mixtures separate into insoluble top phase and clear bottom phase. The IR-spectrum of the insoluble top phase suggests that they contain mostly polymeric components while the IR-spectrum of the clear bottom phase provides evidence that it is essentially free of the polymeric components but comprises surfactant ions. Alternatively, addition of the chloroform solution of (PA-HDTMA)N to the chloroform solution of PVPEt DDS (that is, PVPEt-DDS is present in the mixtures in an excess), leads to the phase separation only at the base-molar ratio the polymeric components rather close to one. The analysis of the homogeneous chloroform mixtures of (PA-HDTMA)N and PVPEt-DDS by means of dynamic light scattering provides evidence that IPEC species are generated. Each particle of such IPECs is thought to have a distinct "core-shell" structure with a compact core assembled from the interacting fragments of the polymeric components and a swollen corona built up by loops and tails of PVPEt-DDS incorporated in such species in an excess, thus providing solubility of the whole particle in chloroform.