A general theory for microstructure in systems of copolymers with strongly interacting groups (SIGs) is proposed. The so-called superstrong segregation limit, corresponding to rather short blocks containing SIGs and strong attraction between them, is considered in detail. In particular, multiplet formation in melts and solutions of ionomers (block ionomers) is studied. It is shown that as the interaction parameter increases, the most stable shape of a multiplet continuously changes from spherical to disklike (oblate ellipsoid). A further increase of the interaction parameter induces another (first order) transition from disklike multiplets to lamellae. The same transitions could be induced by decreasing the average length of ionic blocks in block ionomer systems. The relevant experimental observations are discussed.

The phase structure of a mixture of weakly charged polyelectrolytes in the presence of solvent, counterions, and low molecular salt is studied theoretically. The most important contribution to the free energy of this system is connected with the presence of charges and comes from the translational entropy of counterions and ions of low molecular salt. It is shown that the presence of even a small fraction of charges on the polymers leads in many cases to an essential increase of mixture compatibility. This theoretical prediction is confirmed experimentally. Compatibility enhancement is also achieved for the mixture of stiff and flexible macromolecules if one or both components carry some fraction of charged links. On the basis of a more detailed study of this system we conclude that although the region of macrophase separation in the presence of charged links diminishes, the remaining region of the phase diagram is divided into two parts:In one part we have a true molecular compatibility, while in the other part a microdomain structure is formed which is reminiscent of microdomain structures in melts of block copolymer. The physical reason for microdomain formation originates from the translational entropy of counterions and the impossibility of the violation of the condition of total electroneutrality of the system.

w 'est ltdied thefweticall}' [he behavior ofa collapsed persis[errt macromolecule in poor solvent as a model of collapse [ransi[ion ofsingle double-stranded DN.4 chain, and constructed the diugrum ofs[utcr in the variubk~.s ni[h con!our leng~h #a macromolecule and qualit) of the solvent. H'c~,jimnd[hal [he state (? ftoroidat globule e.~is[s as an intermediate state bet nwn the stales (!f elongated coil ,sta[e and the spherical globule. Our [heorc[icai rewdt .suggest.v[hat a single linear macromolecule with a high degree of polymerization can ,jbrm a toroidal globule. H(n~'ever, [he range in~,hich the toroidal structure is stable decreases as the macromolecule Ien,qrh increases. E.rperimtm[al observation u,ith transmission electron microscope>'has been per~iwmed (o stud> tbeglolndar .struclure~fsingle DNA chain (bacteriophage T4 jbund Ihat an twlrernel>' long chain QST4 DN.4 (166 kbp),~~itha contour length of 56 pm, acIually,ftjrm.s a toroidal globule, and that isotropic .vpht~ri

Microheterogeneities in positively charged gels of diallyldimethylammonium bromide copolymerized with acrylamide and negatively charged gels of sodium and cesium methacrylate copolymerized with acrylamide appear as a result of the collapse of these gels in poor solvents (waterethanol mixtures). Three possible reasons for microheterogeneities are analyzed: the polyelectrolyte effect (i.e., competition between the attraction of the uncharged parts of the chains in poor solvent and electrostatic repulsion coupled with osmotic pressure of counterions), the ionomer effect (i.e., the formation of ionomer multiplet structure), and vitrification (i.e., partial formation of glassy kinetically frozen polyacrylamide-rich regions). Both macroscopic observations and SAXS experiments were made. The dry and water-swollen gels immersed in the water-ethanol mixtures show different final states at high ethanol contents, which proves the existence of kinetically frozen structures for these cases. For highly charged cationic gels we observed an increase of the scattering exponent which correlates with the volume phase transition while for smaller charge density this increase occurs at higher ethanol contents with the appearance of kinetically frozen structures. These results suggest that in the former case the microdomain structure appears mainly as a result of the ionomer effect while in the latter case the main factor is partial vitrification. In contrast to recent results in purely aqueous systems, no SAXS scattering maxima were observed, apparently due to the high irregularity of the microstructures.

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