A. D. Pomogailo

Mechanical properties of epoxy composites based on silver nanoparticles formed in situ

The mechanical and thermomechanical properties of metal-containing epoxy composite films based on silver nanoparticles synthesized in situ are investigated. There is a nonmonotonic dependence of the mechanical properties on the concentration of silver myristate used as a precursor. It is found for the first time that the breaking strength and elastic modulus increase by a factor of 1.8–1.5 relative to those of the unmodified matrix at a small concentration of precursor nanoparticles (on the order of 0.1 wt %). DSC and thermomechanical studies reveal that the glass-transition temperature decreases slightly (by 5–6°C) as the precursor concentration is increased to 0.5 wt %, thereby suggesting a weak plasticization of the modified epoxy matrix. On the basis of the spectrophotometry data measured in the region of surface plasmon resonance of silver nanoparticles (420–425 nm) and SEM data, it is inferred that the in situ strengthening of an epoxy nanocomposite based on epoxy resin ED-20, triethylamine, and silver myristate is attained because silver nanoparticles smaller than 20 nm in size and having a narrow particle-size distribution are formed during curing.

Hybrid polymer-immobilized palladium nanoparticles: Preparation and catalytic properties

A new approach to the synthesis of mixed-type immobilized catalysts was developed: the frontal polymerization of a metal-containing monomer in the presence of a highly dispersed mineral support. The synthesis of an acrylamide complex of Pd(II) nitrate on the surface of SiO2, Al2O3, or C and its subsequent polymerization and reduction resulted in the formation of an organic-inorganic composite that included nanosized Pd particles stabilized by a polymer matrix and an inorganic support. The resulting hybrid nanocomposites are efficient and selective catalysts for the hydrogenation reactions of cyclohexene and alkene and acetylene alcohols.

Preparation of nanostructured materials through thermolysis of metal chelate complexes

We demonstrate that nanocomposites (metals and metal carbides and sulfides) can be produced by thermolysis (370 and 600°C) in a self-generated atmosphere using Cu(II), Co(II), and Ni(II) 2-hydroxy- and 2-N-tosylaminobenzaldehyde azomethine bis-chelates as precursors.

Metal-containing nanoparticles with core-polymer shell structure

Metal-polymer nanocomposites, which comprise nanoparticles of metals and/or their oxides and carbides uniformly distributed in stabilizing polymer matrices, are prepared through solid-phase polymerization of metal-containing monomers followed by controlled thermolysis of synthesized metal-containing polymers. Using X-ray diffraction, electron microscopy, ferromagnetic resonance, and IR spectroscopy, it is shown that nanoparticles present in these systems have a characteristic core-shell structure that comprises a metal-containing core and a surface layer, i.e., a polymer shell. Parameters of the components are estimated.

Synthesis and reactivity of metal-containing monomers: 74. Azomethine copper complexes as modifying agents of epoxy matrices

The effect of additives of copper azomethine complexes of different structure on the character of polycondensation and physicomechanical properties of the obtained metal-containing epoxy polymers was studied. It was shown by the DSC method that the thermal stability of the starting CuII azomethine complexes depended on their structure and nature of polar functional groups. The physicomechanical properties of the unmodified and modified epoxyamine polymers at different ratios of functional groups were compared. The additives of CuII azomethine complexes of 0.42–0.43 wt.% were shown to increase the impact strength of the polymers at the ratio [NH]/EG = 1.07–1.13 (EG is epoxy group).

Two-phase frontal polymerization of metal-containing monomers

A mathematical model of two-phase frontal polymerization in a moving conversion layer is proposed. Using fractional differential-integral calculus, an analytical solution for temperatures in the vicinity of the phase boundary (melting-polymerization) and the dependence of temperature at the front on the rate of the motion of the phase transition boundary are obtained. A formula for the front advancement rate that agrees with the experimental results is found, and a method for estimating the effective activation energy of frontal polymerization is proposed.

Formation of metal-containing nanoparticles in polymer matrix. Computer simulation of clusterization kinetics during the solid-phase thermal decomposition of metal-containing precursors

The scheme of computer simulation of the dynamics of the formation of metal-containing clusters in a polymer matrix during the solid-phase thermolysis of corresponding precursors is developed. The kinetics of particle nucleation and growth is studied within the framework of the model of diffusion-limited aggregation by the combined marching and Monte Carlo methods. Polymer media with different structural organization such as isotropic (globular) and anisotropic (layered and fibrillar) media are considered. Deterministic algorithms of the model are the decomposition of reactive metal-containing groups of a polymer, solid-phase diffusion of particles, and cluster dissociation. The proposed scheme makes it possible to visualize the process of cluster formation.

Synthesis and reactivity of metal-containing monomers 72. Monomeric and polymeric metal acetylenecarboxylates and their nanocomposite products: synthesis, structures, and properties

Methods for the synthesis of a number of transition metal acetylenedicarboxylates were developed. The ways and conditions for their polymerization were studied. The polymerization of metal acetylenedicarboxylates was accompanied by the formation of polyconjugated chains. Controlled thermolysis of metal acetylenedicarboxylates yielded matrix-stabilized metal nanoparticles. The microstructures and magnetic properties of the nanocomposites obtained were examined.

Thermal polymerization of cobalt(II) and nickel(II) acrylates: Use of in situ dielectric measurements

In situ dielectric spectroscopy at frequencies ranging from 1 to 105 Hz was used to study chemical transformations during the heating of cobalt(II) and nickel(II) acrylates from −160 to +400°C. On the basis of analysis of the evolution of dielectric relaxation time spectra, processes that correspond to three macroscopic stages in different temperature intervals were distinguished: dehydration, solid-state thermal polymerization, and decarboxylation of metallopolymers. These processes lead to the formation of a polymer matrix that stabilizes nanosized metal or metal oxide phases. In the case of cobalt acrylate, the crosslinking step occurs in a temperature interval other than that of polymerization. It was found that electric conductivity varies over six orders of magnitude upon the formation of the nanosized metal phase.

SYNTHESIS AND REACTIVITY OF METAL-CONTAINING MONOMERS 50. EVOLUTION OF SHORT-RANGE SURROUNDING OF FE ATOMS DURING THERMAL TRANSFORMATION OF FE3O(OOCCH =CHCOOH)6OH.3H2O

Thermal transformations of FeIII maleate, [Fe3O(OOCCH=CHCOOH)6]OH·3H2O (1), in an autogenerated atmosphere and the change in the short-range surrounding of Fe atoms during thermolysis were studied. The thermal transformations of1 are accompanied by the following processes: dehydration with simultaneous rearrangement of the ligand environment and formation of maleic acid, and polymerization of the rearranged monomer and its decarboxylation at high temperatures. In the initial stage of decarboxylation, the destruction of the metal-carboxylate Fe3O complex occurs followed by the formation of the Fe−Fe bond (r=0.246 nm). The oxidation of the Fe atoms is observed when the thermolysis duration increases.