A. Yu. Shaulov

Sol-gel synthesis and investigation of hybrid organic-inorganic borosilicate nanocomposites

Borosilicate sols based on tetraethoxysilane and boric acid (or trimethyl borate) are synthesized. It is demonstrated that the introduction of organic oligomers into borosilicate sols changes the gelation kinetics, affects the composition and structure of the prepared nanocomposites, and makes it possible to produce so-called ormoborosils. Ultrasonic treatment has a strong effect on the gelation kinetics in borosilicate sols, the characteristics of the sol-gel system, and the structure and composition of the borosilicate composites. The phase composition of the synthesized xerogels is investigated by thermal analysis, and the chemical composition is studied by IR spectroscopy. The inference is made that the sol-gel synthesis of borosilicate nanocomposites leads to the formation of multilevel fractally aggregated nanocomposites.

Synthesis of an inorganic-organic polymer blend from orthoboric acid and caprolactam

The possibility of modifying boron polyoxide with an oligomeric amide upon thermal dehydration of orthoboric acid and oligomerization of caprolactam in a common melt is shown. The products obtained after thermal pretreatment of the initial blend containing 30 wt % caprolactam are investigated. It is shown that the main processes at T < 200°C are dehydration of orthoboric acid and hydrolysis of caprolactam with the formation of e-aminocaproic acid. At temperatures of 225–260°C, the predominant process is the formation of boron polyoxide and a caprolactam-based oligomeric product. The data of 11B NMR spectroscopy show that the chemical transformations of caprolactam occur against the background of the N:B donor-acceptor interaction. The two-dimensional [11B-1H] heteronuclear correlation spectrum indicates that the systems obtained upon thermal treatment are solid solutions.

Monoelemental polymers: Structure and properties

Monoelemental polymers with various chemical constitutions and different spatial structures (linear Te n , Se n , and S n ; planar graphite C n , black phosphorus P n , As n , Sb n , and Bi n ; and chemically bonded three-dimensional diamond C n , B n , Si n , and Ge n ) were considered and categorized as a class of covalent macromolecular compounds. Quantitative expressions relating the thermal (melting point, thermal expansion coefficient, heat conductivity) and elastic (microhardness, bulk compression modulus of elasticity) properties of polymers to the energy of intra-and intermolecular interactions and the equilibrium length of chemical bonds in the crystalline and glassy states are given. A numerical correlation between the spatial structure of polymers and their thermal and elastic properties was obtained. The hypothetical melting point of diamond at normal pressure was calculated as T f = 3155 K.

Tribomechanical effects in dispersion-filled polymers

Abstract The interconnection between the elastic-strain properties of dispersion-filled polymers and the boundary interactions between the filler and bond is considered. The contributions of the adhesional and mechanical components of the coefficient of friction between them to the change in Youngs modulus of the material on filling is discussed. Tribomechanical effects can be observed in unmodified dispersion-filled polymers, in composites showing inter-phase modification by a viscous liquid, and also in composites containing anti-adhesive. A model of dispersion-filled polymers with zero adhesion or ideal slipping between the components has been realized experimentally.

Relaxational characteristics of the homogeneous, crosslinked, diepoxide-polyepoxide system

Abstract A process is discussed, of modification or “maacromolecular reinforcement” of a highly crosslinked polymer, by linear macromolecules that are chemically active towards the crosslinking system and are soluble in it. It is shown that the dimensions of the modifier coil do not change during curing and are close to its dimensions in dilute solution. Addition of the linear polymer brings about an increase in physical interaction between the structural elements of the crosslinked polymer network, and to levelling out of the structural inhomogeneity of the cured system.

Study of the dynamic interactions of macromolecules in concentrated polymer solutions using spin labelling

The intermolecular spin exchange rate constants and the rotational diffusion correlation times have been measured for spin labels (side groups of poly(glycidyl methacrylate)) in concentrated polymer solutions (cp ⩽ 0.50 g/ml). The spin exchange was measured with average spacings of ∼30A between the labels. It is shown that the rate of translational and rotational mobility of the labels at cp ⩽ 0.25 g/ml decreases in thermodynamically “good” solvents by a factor of ∼1.6 as the polymer concentration rises. On this basis it is proposed that in concentrated polymer solutions the “freely permeating coils” model (average degree of polymerization of the polymer P=690) should hold up to cp=0.25 g/ml. An analysis of the results obtained and of data in the literature leads to the tentative proposal of a threshold polymer concentration in thermodynamically “good” solvents at which solutions may become “insensitive” to their quality (at the iso point).

The rate constants of macroradical recombination as a function of chain length (review)

The rate constant of spin exchange ks and the diffusion coefficients of the stable radicals of polyoxyethylene derivatives (average degree of polymerization P = 25, 47 and 140) and of polydimethylsiloxane (P = 15, 29 and 97), were investigated as functions of chain length in various solvents. The results were compared with the rate constants of diffusive mutual termination kt for macroradicals of various lengths. The dependence of ks and kt on chain length conform to a single rule. Macroradicals in the P = 15−105 range were found to have their termination reactions limited chiefly by the mobility of the reactive centres, which depends on the diffusion of the entire macromolecules. Coefficient D is described by the Smolukowski equation in which the effective radius of reaction is that of the reactive centre. A model for the mutual termination of the macroradicals, i.e. the “freely permeated coils” model, has k ∼ P0·9±0·1 as a valid function (in the case of good solvents). It is concluded that the reactivity of the reactives centres at P > 15 depends on chain length in the recombination reactions. The electron-exchange reactions will result just as effectively in ESR line broadening with pairs of radicals as in the recombinations.

Orientation Effects in Hybrid-Polymer Mixtures

Composites based on melts of boron-oxide oligomer (BOO) and low-density polyethylene (LDPE) in the polyoxide-concentration range of 0–64 vol % were synthesized. The measurements of the thermomechanical and mechanical properties of the composites showed the incompatibility of the mixture components. The abnormal increase in the strength and the Young’s modulus of the LDPE/boron-oxide oligomer mixtures under the tension of molded composite specimens was registered in the range of 25–50 vol % polyoxide. The anomalies were explained as being due to polyoxide-fiber formation and confirmed by the electron-microscopy images. The abnormal changes in the differential pressure in a melt flow and the torque of an extrusion auger were observed in the same polyoxide-concentration range, which was explained by the polyoxide orientation in a melt flow and its planar structure. The chemical structure of boron-oxide oligomer exposed to extrusion mixing and its distribution within a molded specimen of the mixture were analyzed by IR spectroscopy. The opportunity to synthesize hydrolytically stable composites in a wide range of ratios owing to the polyoxide encapsulation in a polyethylene matrix was shown.

Composite material based on fluoroplast and low melting oxyfluoride glass

The present work summarizes the results of studies of the samples fabricated through extrusion blending of mixtures composed of the perfluorocarbon polymer (polyvinylidene fluoride, PVDF), which presently undergoes intensive studies, and the inorganic glass (BF-glass) of the composition 3B2O3-97(40SnF2-30SnO-30P2O5). It is revealed as a result of application of the suggested technique the composite material whose structure depends on the component ratio in the mixture (from individual areas formed by each component to homogeneously distributed composite particles) has been fabricated. The peculiarities of formation of composites were studied on the basis of the results of studying their morphology, molecular structure and phase composition. It was revealed the preservation of the polymer molecular structure and the absence of interaction with the glass in the fabricated samples. We found that in the process of sample fabrication there occur melting of the mixture, mixing of particles and changing of the p...

Methods of investigation radiographic method for studying the structure of polymer composites

Abstract For investigating the structure of a composite material — its dimensions, form and distribution in space of the particles of one of its components, the method of radioautography was applied. To this end, a tritium-labelled divinylstyrene block-copolymer was synthesized; this was applied to the surface of a dispersed filler and introduced into a polyethylene matrix. From microphotographs evidence was obtained indicating that the elastomer encapsulating the filler, after forming of the material predominantly remains at the surface of the filler. A histogram of the distance distribution between the nearest elastomer particles is presented. The probability of a uniform distribution of distance between the nearest elastomer-coated particles (0·65), and the mean thickness of the elastomer layer (25 nm) were evaluated.