V. B. Rogacheva

From triple interpolyelectrolyte-metal complexes to polymer-metal nanocomposites

Nanocomposite polymer materials containing metal or metal oxide particles attract growing interest due to their specific unique combination of physical and electric behavior. Stoichometric triple interpolyelectrolyte-metal complexes (TIMC) are insoluble in water and in aqueous organic media and may include high content of metal ions; concentration of ions is easy to vary in such polymeric systems. Reduction of metal ions is a common method for obtaining nanoparticles. Interpolyelectrolyte complexes reveal high permeability for polar low-molecular substances and salts. Such swelling behavior is important for the reduction of metal ions included in these solids. The properties of triple interpolyelectrolyte-metal complexes and preparation of nanocomposites from these materials using various methods of metal ion reduction are discussed in this work.

Polymeric stabilizers for protection of soil and ground against wind and water erosion

The article is devoted to the design, development and application of a new generation of binders for various dispersed systems, including soil, ground, sand, waste rock and others. The binders are formed by interaction of oppositely charged polyelectrolytes, both chemically stable and (bio)degradable. The fundamental aspects of interpolyelectrolyte reactions are discussed; the IPC structure and properties of the resulting interpolyelectrolyte complexes (IPCs) allow considering them as unique and universal binders. Numerous results of laboratory experiments and field trials of the IPC formulations are presented. In particular, large-scale tests have been done in the Chernobyl accident zone where the IPC binders were shown to be effective means to suppress water and wind erosion thereby preventing a spread of radioactive particles (radionuclides) from contaminated sites. Ecologically friendly IPC compositions are described, including those based on commercially available polymers; prospects for improving their efficiency and extending the range of their possible use are discussed.

Interpolymer Complexes Formed by Polyelectrolyte Gels

The approaches to synthesis and modification of polymers based on the assembly of chemically complementary macromolecules have been recently widely developed. Interpoly electrolyte complexes (IPEC) are more common polymers of this type. They are the products of interaction between oppositely charged polyelectrolytes (Bixler and Michaels, 1969; Tsuchida and Abe, 1982). IPEC are of special interest as the effective adhesives for solving ecological, biomedical and agrotechnological problems due to their unique structure (Zezin and Baranovskii, 1983; Zezin et al., 1987). The utilization of cross-linked polyelectrolytes gives new opportunities for the construction of polycomplex substances and materials. These opportunities are based on the phenomenon of active transport of linear polyelectrolytes into oppositely charged networks (Rogacheva et al., 1988; Kabanov et al., 1988; Kabanov et al., 1989). The driving force of this transport and the mechanism of transport of linear polyions in polyelectrolyte gels are directly connected with the interpolyelectrolyte reaction (IPR) which proceeds between polyions and gel. Slightly cross-linked polyelectrolytes absorb oppositely charged linear polyions from aqueous solutions. This gradual uptake is followed by production of small counter ions of linear and cross-linked polyelectrolytes. For example, the reaction between slightly cross-linked poly(2-di methylaminoethyl methacrylate) (PDMA) and linear poly(acrylic acid) (PAA) is presented in Scheme (I).

Competing reactions in anionic gel-poly(propylene imine) dendrimer-surfactant ternary systems

Competitive interactions in ternary systems including a lightly crosslinked polyanionic hydrogel, a protonated Astramol™ poly(propylene imine) dendrimer (of first to fifth generation), and an ionic surfactant were studied. It was found that the direction of the substitution reactions in systems containing cationic surfactants depends on the length of the aliphatic radical in the surfactant molecule as well as on the dendrimer generation number. Depending on these parameters, the interpolyelectrolyte complex formed by the network polyanion and the cationic dendrimer is either capable or incapable of sorbing surfactant cations from aqueous solutions, thereby transforming into the network polyanion-cationic surfactant complex with the release of dendrimers to the surrounding solution. It was shown that the substitution reaction in systems containing anionic surfactants leads to the formation of a polyanionic gel reinforced by particles of the dendrimer-anionic surfactant complex.

The effect of the charge of astramol™ poly(propylene imine) dendrimers on interaction with polyanionic gels

The effect of the charge of Astramol™ poly(propylene imine) dendrimers of the third and fourth generations on activated sorption of dendrimer molecules by weakly crosslinked polyanionic networks was studied. It was shown that the formed interpolyelectrolyte complex was markedly enriched in the weakly charged dendrimer as the degree of dendrimer neutralization decreased. As was found, depending on the conditions of sorption of dendrimers by oppositely charged networks, this process leads to the formation of either macroscopically heterogeneous “shell-core” structures or microheterogeneous composites with uniform distribution of micrometer-sized clusters of dendrimer molecules in the gel matrix. The structure of such systems separated at the microphase level was studied by the laser scattering technique. Their high ordering was established, and the reasons behind the formation of various alternative heterophase systems were discussed.

Interaction of ampholyte dendrimers with network polycations and polyanions

The interaction of polyampholyte propylenimine dendrimers of five generations containing peripheral carboxyl and inner tertiary amino groups with lightly crosslinked highly swelling polyelectrolyte gels has been studied. It has been shown that the polyampholyte dendrimers of all five generations are efficiently sorbed by a polyanion sulfur-containing hydrogel (below the isoelectric point) and a polyamine hydrogel (above the isoelectric point) to give rise to interpolyelectrolyte complexes. The composition of interpolyelectrolyte complexes and the equilibrium concentration of the dendrimer in the surrounding solution are appreciably affected by the pH of the medium. Amount of zwitterion pairs in a dendrimer molecule significantly influence the formation of interpolymer salt bonds. The polyampholyte dendrimer can pass from an anionic hydrogel to a cationic one upon a small change in pH near the isoelectric point.

Interaction of ampholyte dendrimers with linear polyelectrolytes

The interaction of ampholyte propylenimine dendrimers containing peripheral carboxyl groups and inner tertiary amino groups with linear polyelectrolytes has been studied. Both in acidic and alkaline media up to pH ∼ pI, dendritic polyampholytes can form interpolyelectrolyte complexes with flexible linear polyanions and polycations. A variation in the composition of complexes with a change in pH is associated with the formation of intramolecular zwitterion pairs in a dendrimer molecule. The ability of interpolyelectrolyte complexes to dissolve in water is shown to be determined by the degree of dissociation of ionogenic groups of the dendrimer not directly involved in the formation of interpolyelectrolyte salt bonds stabilizing the complex. It has been demonstrated that the territorial separation of carboxyl and tertiary amino groups in the polyampholyte dendrimers is reflected in different structures of interpolyelectrolyte complexes formed by dendrimers with oppositely charged linear polyions.

Competitive interactions in hydrogel-interpolyelectrolyte complex systems

Abstract-Substitution reactions between weakly crosslinked anionic hydrogels (network sodium polyacrylate or network sodium poly(2 acrylamido-2-methyl-1-propanesulfonate)) and nonstoichiometric inter-polyelectrolyte complexes formed by a blocking linear sodium polyacrylate and lyophilizing poly(N,N’-diallyl-N,N’-dimethylammonium chloride) in aqueous media have been revealed and studied. It has been found that both sulfonate and carboxylate networks take up a linear polycation via the formation of a stoichiometric interpolyelectrolyte complex, a phenomenon that results in the collapse of the network. In this case, the blocking polyacrylate anions are quantitatively expelled from the particles of the nonstoichiometric watersoluble complex into the environment and occupy lyophilizing polycations uniformly, a circumstance that results in their precipitation and, consequently, the termination of the substitution reaction. This outcome suggests the presence of feedback in the studied processes. The result for carboxylate networks is completely new and nontrivial; it is indicative of the important role of macromolecular architecture in selecting the direction of a process.

Sorption of anionic amphiphilic block copolymers by a network polycation

The interaction of amphiphilic block copolymers comprising an anionic block (polyacrylate or polymethacrylate) and a hydrophobic block (polystyrene, poly(butyl acrylate) or polyisobutylene) with lightly crosslinked poly(N,N-diallyl-N,N-dimethylammonium chloride) is studied for the first time. It is shown that the cationic hydrogel can sorb anionic amphiphilic block copolymers via electrostatic interaction with the corona of block copolymer micelles. The rate of sorption of block copolymer polyelectrolytes is significantly lower than the rate of sorption of linear polyions and is controlled by the lengths of the hydrophilic and hydrophobic blocks and the flexibility of the latter blocks. The sorption of amphiphilic block copolymers is accompanied by their self-assembly in the polycomplex gel and formation of a continuous hydrophobic layer impermeable to water and the low-molecular-mass salt dissolved in it.

Formation and transformations of polyelectrolyte gel-ampholyte dendrimer-surfactant ternary complexes

The reactions of complex gels formed via the sorption of a poly(propylenimine) ampholyte dendrimer of the fourth generation by oppositely charged lightly cross-linked polyelectrolyte hydrogels with ionogenic micelle-forming surfactants have been studied. The sorption of surfactant ions likely charged relative to the complexed ampholyte dendrimer by complex gels is associated with two parallel chemical reactions controlled by the concentration of the surfactant and pH which give rise to the formation of network-dendrimer-surfactant tertiary complexes. The reactions of complex gels with surfactant ions likely charged relative to the network polyelectrolyte make it possible at different solution pHs to prepare both negatively and positively charged hydrogels reinforced by disperse particles of the dendrimer-surfactant complex.