T.A. Pryakhina

Hydrophobic aggregation in aqueous solutions of hydrophobically modified polyacrylamide in the vicinity of overlap concentration

The rheological behavior and hydrophobic association of hydrophobically modified polyacrylamide with 0.5 mol% of hydrophobic n-nonylacrylamide units were studied in the vicinity of the overlap concentration. It was shown that the rheological properties of aqueous polymer solutions are determined by the formation of hydrophobic domains playing a role of physical cross-links between polymer chains. It was observed that a pronounced increase of the viscosity above the overlap concentration is accompanied by the increase of the concentration of hydrophobic domains, but the average size of one domain remains constant.

Molecular mass characterization of polymers with strongly interacting groups using gel permeation chromatography–light scattering detection

This work is aimed at studying dilute solution behavior and developing techniques for the proper Mr characterization of polymers with strongly interacting groups. In particular, we have studied ionomers based on poly(dimethylcarbosiloxane) with carboxylic groups and hydrophobically modified polyacrylamide and its charged terpolymer. Gel permeation chromatography-light scattering (GPC-LS) study of organosilicon ionomers allowed us to follow molecular mass distribution evolutions during approximately a week that evidenced the gradual dissolution of clusters formed in bulk polymers. The rate of this process depends on the polymer composition and its preliminary treatment. Observed aggregates arre found to be stable during the procedure of chromatographic analysis. For characterization of hydrophobically modified polyacrylamide and its charged derivatives, we have used aqueous NaNO3-acetonitrile mixed solvent. Fluorescence spectroscopy with pyrene as a probe did not reveal any hydrophobic association in this solvent in contrast to aqueous solutions. Reversed-phase retention as well as polyelectrolyte exclusion were suppressed at GPC analysis. GPC-LC and classical LS methods gave consistent results for uncharged and weakly charged polymers. In the case of highly charged and highly hydrophobic terpolymers LS results evidenced association, while OPC-LC gave credible Mr values. We can conclude that in the last case, the observed association was weak enough to be disrupted in the coarse of chromatography.

Nanocomposites Based on Epoxy Resin and Silicon Dioxide Particles

The cure of an epoxy resin (3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate) in the presence of silica nanoparticles modified by 3-(triethoxysilyl)propylsuccinic anhydride has been studied. Optimal conditions for the preparation of optically transparent polymer nanocomposites with increased glass transition temperatures are determined. The glass transition temperatures of the above nanocomposites are 50–70°C higher than those of the unfilled epoxy resin synthesized under the same conditions (100°C).

Rheological properties of solutions and gels of combined systems hydrophobically modified polyacrylamides-new viscoelastic cationic surfactants

The rheological properties (viscosity and dynamic elasticity modulus) of solutions and gels of combined systems composed of hydrophobically modified polymers containing main-chain charged groups or lacking these groups and of newly synthesized viscoelastic cationic surfactants with different amounts of OH groups and long nonpolar saturated and trans monounsaturated radicals have been studied. It has been shown that the maximum viscosity of solutions of polymer-surfactant complexes corresponds to the very low concentration of the surfactant. Regions where homogeneous and heterogeneous combined solutions and gels exist are considered. An increase in the viscosity of the combined solutions with temperature is discovered and discussed. The synergistic effect of polymers and surfactants is demonstrated, and a more efficient role of surfactants in the case of uncharged polymers is revealed. The roles of the number of OH groups and the length of the nonpolar radical in a surfactant molecule and a difference in the properties of systems containing surfactants with saturated and unsaturated radicals are considered.

Molecular-Mass Characteristics and Association Behavior of Weakly Charged Hydrophobically Modified Poly(acrylamides)

The evolution of compositional heterogeneity and molecular-mass distribution in the course of micellar polymerization of weakly charged hydrophobically modified poly(acrylamides) has been studied. The relationship between the molecular characteristics, association behavior, and rheological properties of aqueous solutions and gels of these copolymers has been examined. The molecular-mass distribution broadens with conversion owing to accumulation of a low-molecular-mass fraction depleted of the hydrophobic monomer. A change in the molecular-mass distribution has a strong effect on the viscoelastic behavior of the polymers. The properties of the copolymers are dependent on the pH of the reaction mixture: the copolymers prepared in the alkaline medium show a more pronounced ability to experience hydrophobic aggregation than the copolymers prepared in the acidic medium. The aqueous solutions and the gels of these polymers are characterized by higher viscosities and dynamic moduli. The rheological characteristics of the hydrophobically modified poly(acrylamides) are improved with an increase in both their molecular mass and the length of hydrophobic sequences with a constant molecular mass.

Rheology of Hydrophobically Modified Polymers

A study has been made of the rheological characteristics of the aqueous and water‐salt solutions and gels of one class of hydrophobically modified polymers: acrylamide copolymers with a hydrophobic monomer which can be either acrylamide with a hydrophobic “tail” consisting of 9 or 12 carbon atoms or methacrylate with the same “tail.” It has been shown that a sharp growth in the viscosity of the solutions and in the limiting stress, the highest Newtonian viscosity, and the elastic modulus of the gels is the greater, the larger the length and the number of hydrophobic groups in the copolymer and the smaller the amount of a surfactant in the process of its synthesis, which leads to a hydrophobicity growth of the copolymer. Consideration has been given to the role of the number of charges introduced into the copolymer apart from the hydrophobic groups and to other factors determining the rheological properties of the gels and their resistance to temperature.