A.I. Barabanova

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).

Synthesis of hydrophobically modified poly(acrylamides) in water-in-oil emulsions

High-molecular-mass hydrophobically modified poly(acrylamides) have been prepared via water-in-oil miniemulsion copolymerization of acrylamide and lauryl methacrylate initiated by 2,2′-azoisobutyronitrile. The incorporation of the hydrophobic comonomer into the polymer backbone is indirectly confirmed by the rheological and associative properties of polymer solutions. The copolymers prepared from the reaction mixtures containing less than 5 mol % lauryl methacry late demonstrate the associative behavior in aqueous solutions, as evidenced by fluorescence spectroscopy (a decrease in the polarity parameter of pyrene), static and dynamic light scattering (overestimated effective molecular masses and appearance of a peak due to aggregates), and rheological measurements (a rise of viscosity relative to that of the acrylamide homopolymer). A further increase in the content of lauryl methacrylate leads to formation of polymers possessing limited solubility in water. At the acrylamide-to-hydrophobic monomer equimolar ratio, homopolymers arise along with the insoluble copolymer.

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.

Catalytic properties of diblock copolymers of N-vinylcaprolactam and N-vinylimidazole

Thermoresponsive diblock copolymers of N-vinylcaprolactam (VCL) with N-vinylimidazole (NVI) have been synthesized for the first time through two-stage controlled reversible addition–fragmentation chain transfer (RAFT) polymerization. The resulting diblock copolymers exhibit the same catalytic activity toward p-nitrophenyl propionate (NPP) hydrolysis as “protein-like” copolymers of VCL and NVI. The catalytic activity of the diblock copolymers is likely caused by their structure favorable for the manifestation of catalytic properties, namely, by micelle-like chain conformations with a relatively dense core formed by the more hydrophobic PVCL block and a periphery formed by the hydrophilic poly-N-vinylimidazole (PNVI).

Mesoscopic simulation of the synthesis of enzyme-like catalysts

A model based on the mesoscale simulation technique was developed for predicting the conditions for artificial enzyme formation from N-vinylcaprolactam (VCL) and N-vinylimidazole (NVI) by radical copolymerization of pre-synthesized poly-VCL blocks of different molecular weight with VCL and NVI comonomers. This synthetic procedure gives model copolymer chains. Upon a change in the solvent nature, these chains are able to form compact two-layer globular nanostructures with core–shell type morphology if the fraction of the first poly-VCL block is 25–38% of the total copolymer and the fraction of NVI monomers in the reaction mixture (in the concentration range considered) is maximum.

Structures and Properties of Nanocomposites Based on a Cured Cycloaliphatic Epoxy Resin

The effect of nanoparticles on glass-transition temperature Tg and the elastic modulus of a cycloaliphatic epoxy resin cured with methylhexahydrophthalic anhydride is theoretically analyzed. The analysis was performed with allowance for the following factors: the chemical structure of the polymer, the chemical structures of the nanoparticles and their surfaces if they are modified, the concentrations and shapes of nanoparticles (spherical, plate, cylindrical), the concentration of functional groups on the surfaces of nanoparticles, the energy of intermolecular interaction between a polymer and a nanoparticle, and the possibility of chemical interaction between a polymer and the surfaces of nanoparticles. The most pronounced effect on Tg is exerted by cylindical nanotubes, whose surfaces are modified with OH groups, which give rise to hydrogen bonding. The least effect is exerted by spherical nanoparticles. After the introduction of SiO2 nanoparticles, the elastic moduli of nanocomposites increase by a factor of 1.15 at an amount of nanoparticles up to 20%.