ABSTRACT:The phase state of polyelectrolyte blends based on acrylic copolymers was investigated with differential scanning calorimetry, transmission electron microscopy (TEM), and wedge microinterferometry as a function of the blend composition and ionization of polymer functional groups. A copolymer of N,N-dimethylaminoethyl methacrylate with methyl methacrylate and butyl methacrylate was used as a polybase, a copolymer of methacrylic acid and ethyl acrylate was employed as a polyacid, and the optional plasticizer was triethyl citrate. A correlation was established between an earlier described mechanism of molecular interaction and the behavior of the glasstransition temperature (T g ) of the polymer blends. The T g values of the polyelectrolyte complexes in the gel phase were always higher than T g in the sol phase. This fact implies that intermolecular cohesion dominated the free volume in the stoichiometric polyelectrolyte complexes formed in the gel phase, whereas nonstoichiometric complexes formed in the sol phase were characterized with the predominant contribution of free volume. TEM and interferograms of polyelectrolyte blends showed the signs of anisotropic ordered supramolecular structure formation. A phase-state diagram of the polyelectrolyte blends was constructed. The stoichiometric polyelectrolyte complex was immiscible with parent polymers, forming a separate phase that became melted at elevation of temperature because of complex dissociation. Polyelectrolyte miscibility was supposed to result rather from the chemical reaction of the complex formation than from interdiffusion of the polymer components along the gradient of their concentration.

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Pair interaction parameters for multicomponent polymer blends were found to be deter mined by analyzing the sorption isotherms of common solvent.The necessity of obtaining information on thermo dynamic characteristics of polymer blends does not admit of doubt. Among a variety of characteristics, there are pair interaction parameters (Huggins parameters). 1-3 When these parameters are available, it is possible to establish how the free energy of mixing depends on the polymer blend composition, to evaluate the mutual solubility lim its of the blend components, and to construct the phase diagrams and various sections of these diagrams.Our experience on studies of the phase equilibria in the polymer-polymer systems suggests that it is of crucial importance to obtain information on the pair interaction parameters (χ ij ) by processing experimental data using independent procedures. Clearly, this can be useful for not only solving problems mentioned above but also test ing correctness of statistical theories of polymer melts and solutions.The aim of this work was to determine the pair inter action parameters between the components of multicom ponent polymer blends by analyzing the sorption isotherms of common solvent.According to the Flory-Huggins theory of polymer solutions, 4-7 the expression for the free energy of mixing (∆G m ) of an n component system has the form ,where ϕ i and ϕ j are respectively the concentrations of the ith and jth components in solution (blend) expressed in the volume fraction scale, r i is the degree of polymeriza tion of the ith component, and n is the total number of components in the system. The component concentra tions are related by obvious relationship . A specific feature of the system under study is that the ratio of the polymer concentrations in the blend is the same in all portions of sorption isotherms. This allows such systems to be treated as pseudobinary "sorbate-sorbent" systems characterized by the solvent concentration (ϕ S ) and the polymeric sorbent concentration ϕ P (ϕ S + ϕ P = 1). Clearly, the polymer concentrations in the sorbent in all portions of sorption isotherms are given bywhere k i is the concentration of the ith polymer in the blend in the absence of solvent. Consider the thermodynamics of mixing of a pseudo binary system assuming constant values of the pair inter action parameters at all concentrations.By substituting expression (2) in expression (1), group ing similar terms, and denoting the degree of polymeriza tion of the polymeric sorbent (r P ) as , we get ,where m is the number of polymeric components in the sorbent. The third and fourth terms represent the en tropy dependent part of the free energy of mixing of poly mers (∆G m,P ) in the absence of solvent .(4)

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