ИСТИНА

Interpolyelectrolyte complexes (IPECs) resulting from the electrostatic interaction between oppositely charged macromolecules attract considerable attention not only from a fundamental point of view but also as promising and easily available polymeric reagents and materials with intelligent, in many cases unique, properties for their applications in biotechnology, ecology, and medicine. IPECs are generally prepared throgh direct mixing aqueous solutions of the oppositely charged macromolecules. At the same time, interpolyelectrolyte complexation proceeding in organic media has received only a very scarce attention so far, though it is expected to offer effective control of equilibrium/kinetics of such process and, as a consequence, properties of the resulting macromolecular assemblies via a variation of polarity of the surrounding organic media. Besides, in organic media of low polarity one can even completely cancel hydrophobic interactions, obviously always manifesting themselves in aqueous media, to have the interpolyelectrolyte complexation to be purely electrostatic. The main problem arising, when dealing with interpolyelectrolyte complexation in organic media, is that generally polyelectrolytes are poorly soluble or even totally insoluble in organic solvents, especially in organic solvents of low polarity. To overcome this problem, one may exchange low molecular weight inorganic counterions (or protons) for much more hydrophobic surfactant counterions to make them easily soluble in organic solvents, in particular in organic solvents of low polarity. Then, the interaction between complementary polyelectrolytes, both having corresponding surfactant counterions, is expected to result in the formation of IPECs, a concomitant release of pairs of the oppositely charged surfactant ions, which were previously associated with charged groups on polymers, into the bulk solution being thought to be a driving force for such a process because it leads to a significant increase of mixing entropy of the system. This contribution considers the formation of IPECs in chloroform. As anionic polyelectrolytes, poly(acrylic acid) stars, (PAA)N, with the number of arms N = 5, 8, and 21 (DPn(arm) = 100) were taken. As a cationic polyelectrolyte, poly-4-vinylpyridine exhaustively quaternized with ethylbromide, PVPEt Br, (DPw = 600) was used. Hexadecyltrimethylammonium bromide, HDTMA Br, and sodium dodecylsulfate, DDS Na, were chosen to transform the corresponding polyelectrolytes into their soluble in chloroform modified forms, viz., (PA HDTMA)N and PVPEt DDS. On addition of the chloroform solutions of PVPEt DDS to the chloroform solution of (PA HDTMA)N (that is, (PA HDTMA)N is present in the excess), the pronounced phase separation is observed even upon incorporation of first portions of the titrant, thus undoubtedly evidencing the formation of insoluble IPECs, that is, (PA)N PVPEt. Turbidity reaches the maximum at nearly equivalent base-molar ratio of the polymeric components in the mixtures. 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 it contains mostly polymeric components, that is, (PA)N and PVPEt, while the IR spectrum of the clear bottom phase evidences that it is essentially free of the polymeric components but comprises the surfactant ions, that is, HDTMA and DDS. Alternatively, addition of the choloform solution of (PA HDTMA)N to the chloroform solution of PVPEt DDS (that is, PVPEt DDS is present in the excess), leads to the phase separation only at base-molar ratios of the polymeric components in the mixture close to 1 : 1. The analysis of the homogeneous mixtures of (PA HDTMA)N and PVPEt DDS in chloroform by means of dynamic light scattering evidences that soluble in chloroform IPEC species are generated. Each particle of such IPEC is thought to have a "core-shell" structure with a compact core assembled from interacting fragments of the oppositely charged polymeric components and a swollen corona built up by loops and tails of PVPEt DDS incorporated in such species in an excess.