A. B. Zezin

Water-Soluble Interpolyelectrolyte Complexes of Polyisobutylene-block-Poly(methacrylic acid) Micelles: Formation and Properties

We report on interpolyelectrolyte complexes (IPECs) formed by micelles of ionic amphiphilic diblock copolymers with polyisobutylene (PIB) and poly(sodium methacrylate) (PMANa) blocks interacting with quaternized poly(4-vinylpyridine) (P4VPQ). The interpolyelectrolyte complexation was followed by turbidimetry and small angle neutron scattering (SANS). The data obtained by means of a combination of SANS, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (cryo-TEM) provide evidence on the core-shell-corona structure of the complex species with the shell assembled from fragments of electrostatically bound PMANa and quaternized P4VPQ fragments, original PIBx-b-PMAAy micelles apparently playing a lyophilizing part. The complex formation is followed by potentiometric titration as well. This process is initially kinetically controlled. In the second step larger aggregates rearrange in favor of smaller complexes with core-shell-corona structure, which are thermodynamically more stable. An increase in ionic strength of the solution results in dissociation of the complex species as proven by SANS and analytical ultracentrifugation (AUC). This process begins at the certain threshold ionic strength and proceeds via a salt-induced gradual release of chains of the cationic polyectrolyte from the complex species.

Multi-liposomal containers

Small unilamellar liposomes, 40-60 nm in diameter, composed of anionic diphosphatidylglycerol (cardiolipin, CL(2-)) or phosphatidylcerine (PS(1-)) and zwitter-ionic egg yolk lecithin (EL) or dipalmitoylphosphatidylcholine (DPPC), electrostatically complex with polystyrene microspheres, ca. 100 nm in diameter, grafted by polycationic chains (spherical polycationic brushes, SPBs). Polymer/liposome binding studies were carried out using electrophoretic mobility (EPM), dynamic light scattering (DLS), fluorescence, conductometry, differential scanning calorimetry (DSC), and cryogenic transmission electron microscopy (cryo-TEM) as the main analytical tools. By these means a remarkably detailed picture emerges of molecular events inside a membrane. The following are among the most important conclusions that arose from the experiments: (a) binding of liposomes to SPBs is accompanied by flip-flop of anionic lipids from the inner to the outer leaflet of the liposomal membrane along with lateral lipid segregation into islands. (b) The SPB-induced structural reorganization of the liposomal membrane, together with the geometry of anionic lipid molecules, determines the maximum molar fraction of anionic lipid (a key parameter designated as ν) that ensures the structural integrity of liposomes upon complexation: ν=0.3 for liposomes with conically-shaped CL(2-) and ν=0.5 for liposomes with anionic cylindrically-shaped PS(1-). (c) The number of intact liposomes per SPB particle varies from 40 for (ν=0.1) to 13 (ν=0.5). (d) By using a mixture of liposomes with variety of encapsulated substances, multi-liposomal complexes can be prepared with a high loading capacity and a controlled ratio of the contents. (e) In order to make the mixed anionic liposomes pH-sensitive, they are additionally modified by 30 mol% of a morpholinocyclohexanol-based lipid that undergoes a conformational flip when changing pH. Being complexed with SPBs, such liposomes rapidly release their contents when the pH is reduced from 7.0 to 5.0. The results allow loaded liposomes to be concentrated within a rather small volume and, thereby, the preparation of multi-liposomal containers of promise in the drug delivery field.

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.

Phase separation in a poly(acrylic acid)-polycation system in acidic solutions

Phase separation in aqueous solutions of mixtures of poly(acrylic acid) with polycations [poly(diallyldimethylammonium chloride), poly(1,2-dimethyl-5-vinylpyridinium methylsulfate)] in the presence of decimolar hydrochloric acid has been studied by static and dynamic light scattering. The systems are characterized by the upper critical solution temperature. The temperature-dependent association of macromolecules is observed in the single-phase region. A decrease in temperature leads to phase separation; the composition of the diluted phase is determined by the temperature and composition of the initial mixture; and the composition of the concentrated phase remains almost invariable. The occurrence of association in the mixtures is probably the formation of interpolymer complex due to ion-dipole interactions between the carboxyl groups of poly(acrylic acid) and the functional groups of the polycation.

Homophase and heterophase polymerizations of butyl acrylate mediated by poly(acrylic acid) as a reversible addition–fragmentation chain-transfer agent

The radical polymerization of n-butyl acrylate in organic, aqueous, and water–alcohol media in the presence of poly(acrylic acid) containing a trithiocarbonate group within the chain is studied for the first time. It is shown that in nonselective solvents (1,4-dioxane and DMF) poly(acrylic acid) serves as a reversible addition–fragmentation chain-transfer agent and the triblock copolymer poly(acrylic acid)–block–poly(n-butyl acrylate)-–block-poly(acrylic acid) is formed. In aqueous and aqueous–organic media (under conditions of emulsion, dispersion, and miniemulsion polymerizations as well as polymerization-induced selfassembly), the block copolymer being formed additionally serves as a stabilizer of polymer–monomer particles. The sizes of these particles and the molecular-mass characteristics of the resulting polymers may be controlled via variation in the concentration ratio of the components. It is found that, during polymerization in aqueous media, there is the formation of spherical polymer particles that preserve their morphology in thin films prepared via precipitation of the synthesized dispersion.

Nanostructured polyelectrolyte films for engineering highly sensitive tyrosinase biosensors: Specifics of enzyme-polyelectrolyte structures

The correlation was studied between the activity of tyrosinase electrodes engineered by layer-by-layer deposition technology and the number of PDDA/tyrosinase layers (where PDDA stands for poly(diallyldimethylammonium chloride)). The last deposited layer is the active one regardless of the number of layers. Atomic force microscopy (AFM) characterization of the topology of (PDDA/tyrosinase)1 and (PDDA/tyrosinase)2 films showed that these films have identical structures. The operational stability of tyrosinase biosensors coated with (PDDA/tyrosinase)1 films was examined. Various methods for stabilizing tyrosinase biosensors were tested. Crosslinking with glutaraldehyde (GA) improved 2.5-fold the operational stability of (PDDA/tyrosinase)1 films.

New organoelement polyelectrolytes: Protonated poly(alkylaminophosphazenes)

The organoelement polymer bases poly(methylaminophosphazene) and pol(ethylaminophosphazene) have been synthesized by the solid-phase aminolysis of linear ultrahigh-molecular-weight poly(dichlorophosphazene) and characterized. The related cationic polyelectrolytes have been prepared in aqueous solutions in the presence of HCl. As exemplified by the interaction with sodium polystyrenesulfonate and sodium polyphosphate, the polymers form interpolyelectrolyte complexes with anionic polyelectrolytes.

Magnetic properties of ultrasmall iron oxide nanoclusters in a polymer matrix

The synthesis of iron oxide nanoclusters in the matrix of an interpolyelectrolyte complex based on poly(acrylic acid) and polyethylenimine is described. The effect of the method of cluster formation (by the oxidation or reduction of iron ions) on the magnetic properties of polymer nanocomposites was studied. The influence of the surface modification of iron oxide nanoclusters in a polymer matrix on the interaction of the nanoclusters with the matrix, the appearance of first-order phase transitions, and the disappearance of superparamagnetism were examined. Mössbauer spectroscopy and magnetization measurements were used for identifying first-order magnetic phase transitions or superparamagnetism.

Specifics of polymerization of trimethyl(methacryloyloxyethyl)ammonium methyl sulfate in a sodium dodecyl sulfate solution and the properties of resultant complexes

The specifics of polymerization of trimethyl(methacryloyloxyethyl)ammonium methyl sulfate in the presence of sodium dodecyl sulfate and the properties of complexes that appear as polymerization products or are formed from these products were studied. It was found that the addition of the surfactant to the polymerization medium in sufficiently large amounts changes the polymerization rate and has a substantial effect on the properties of the products, thus reducing their molecular mass and greatly extending the range of existence of soluble complexes.

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.