The structure of wholly aromatic polyesters with bulky side chains: Poly(p-phenylene phenylthioterephthalate)

Poly(p-phenylene phenylthio-terephthalate) (PPTT) forms nematic melts and is highly crystalline in the solid state, despite the probable random 2- and 3-dispo-sition of the S-phenyl substituents. The X-ray pattern of melt-spun fibers of PPTT contains 24 Bragg reflections that are indexed by a monoclinic unit cell with dimensions a = 28.6 Å, b = 4.81 Å, c = 12.57 Å (fiber axis), and γ= 101.6°. The cell contains monomer units of four chains that are arranged in pairs with the thiophenyl side chains interdigitated; successive pairs of chains are staggered by about c/2. We used molecular mechanics modeling to simulate arrays of chains with random 2- and 3-disposition of the side chains on the terephthalic acid units and compared the results with those for an idealized structure in which all the substituents were at the 2-position. The refined model for random substitution is more distorted, but the average separations of the monomer units are within the experimental errors of the observed unit cell dimensions, and their standard deviations are very similar to those derived from the line-broadening data. The potential energy of the model with random substitution is only about 1.9 kcal/mol of monomer higher than that for the model with all-2-substitution, indicating random substitution is not a major problem to the formation of an ordered structure. Compared to the structure formed by the analogous polyester, poly(p-phenylene phenylterephthalate) (PPT), the additional flexibility due to the thioether linkage between the backbone and phenyl side groups in PPTT allows better chain packing both within and between the layers of stacked chains.     

Polymer microspheres for replacement of biological carriers in test systems operating on the principle of latex agglutination reaction

The results of the study of various modification methods of polymer microspheres for their use in immunochemical reactions as bioligand carriers are reported. Ion etching and electron microscopy were used to show that the copolymer microspheres have a porous structure non-uniform in density. The Maillard reaction was used for the first time in the modification of copolymer microspheres by dextrans of different molecular weight as a simplest way of covalent immobilization of saccharides on their surface. The physicochemical properties of polystyrene-divinylbenzene and polyglycidyl methacrylate-ethylene glycol dimethacrylate microspheres modified with diamines and dextrans were determined for the first time. The conditions under which the bioligand (diphtheria toxoid) immobilized on their surface retained the native conformation and the diagnostics obtained on their basis have high sensitivity were revealed.

     

Electron Emission Properties of Self-Assembling Nanodiamond‒Polymer Nanocomposite Coatings

Crystallography Reports - The formation of thin-film coatings from detonation nanodiamond (DND) suspensions on atomically ordered conducting Ni–W substrates by self-assembly in an evaporating...     

Small angle x-ray analysis of the effect of temperature on the self-assembling columnar structures formed by a polymethacrylate with highly tapered side groups and by one of its low molar mass precursors

Small angle X-ray methods have been used to investigate the self-assembling columnar structures formed by a polymethacrylate with large highly tapered side groups, and by one of its low molar mass precursors. The polymer is poly{2-{2-[2-(2-methacryloyloxyethoxy)ethoxy] ethoxy}ethyl-3, 4, 5-tris(p-dodecyloxybenzyloxy)-benzoate} (H12-ABG-4EO-PMA); the precursor is 2-{2-[2-(2-hydroxyethoxy)-ethoxy]ethoxy}-ethyl-3, 4, 5-tris(p-dodecyl-oxybenzyloxy)benzoate (H12-ABG-4EO-OH). Both the polymer and the precursor form three dimensionally ordered structures at room temperature, consisting of hexagonally packed cylinders with diameters in the region of 60 and 53Å, respectively, in which the interiors of the columns probably have helical arrays of the stacked tapered groups. At higher temperatures these are converted to columnar hexagonal (ϕ_h) liquid crystalline phases. At temperatures close to this transition for the precursor we detect two coexisting columnar structures, with the ϕ_h structure having a diameter approximately 1Å higher than that in the solid state. For the polymer, the data are not so well resolved, and coexisting phases cannot be resolved. However, the changes in column dimensions are larger than for the precursor. Conversion of the room temperature phase to the ϕ_h phase at 40°C results in an increase of 3Å in the diameter, which then declines by approximately the same amount as the temperature rises to 90°C, close to the isotropization point. Cooling to room temperature does not immediately restore the room temperature structure. Rather, we obtain a quenched ϕ_h structure, with a column diameter almost 10% higher. These dimensional changes correlate well with the changes in diameter with temperature seen for the bulk fiber, and suggest a continuous rearrangement of the interiors of the columns in the ϕ_h phase, such as a partial unwinding of a disordered helical structure.     

Study of the slow electrolyte-induced changes in the TiO<Subscript>2</Subscript> hydrosol structure

Slow changes in the TiO₂ hydrosol structure induced by a small KCl additive were studied using the small-angle X-ray scattering. The initial sol of anisometric anatase nanocrystals stabilized by HCl was prepared. After addition of KCl scattering curves were measured regularly for 2 years. It was established the formation and the accumulation of small dense aggregates. A model of the slow structural changes in the TiO₂ sols with electrolyte additives comprising the two steps of aggregation was proposed. At first the larger anatase nanocrystals combine slowly forming the small dense aggregates through the oriented attachment mechanism. Then, at the critical size of such aggregates, they coagulate quickly forming the looser particles.     

Biodegradable blends obtained via reactive blending of polylactide and polyamide-6

Blends of polyamide-6 and polylactide are prepared via reactive compatibilization. Their phase morphologies and compositions are characterized by the methods of IR spectroscopy, optical and scanning electron microscopy, NMR, dynamic mechanical analysis, and continuous extraction in a boiling solvent. It is shown that the formation of hydrogen bonds between polylactide and polyamide-6 substantially improves the compatibility of components. A large proportion of a copolymer is formed as a result of interchain exchange between polyamide-6 and polylactide molecules. The results open new possibilities to produce commercially attractive biodegradable materials with high mechanical and thermophysical characteristics.     

Small-angle x-ray scattering study of polymer structure: Carbosilane dendrimers in hexane solution

The three-dimensional organization of monodisperse hyper-branched macromolecules of regular structure—carbosilane dendrimers of zero, third, and sixth generations—has been studied by small-angle X-ray scattering (SAXS) in solution. The use of modern methods of SAXS data interpretation, including ab initio modeling, has made it possible to determine the internal architecture of the dendrimers in dependence of the generation number and the number of cyclosiloxane end groups (forming the shell of dendritic macromolecules) and show dendrimers to be spherical. The structural results give grounds to consider carbosilane dendrimers promising objects for forming crystals with subsequent structural analysis and determining their structure with high resolution, as well as for designing new materials to be used in various dendrimer-based technological applications.     

Analyzing the Mechanical Behavior of Polymer and Composite Materials by Means of Unique Method of Deformation Calorimetry

Results are presented from long-term investigations of a wide range of polymer systems, varying from elastomers and thermoplastic elastomers to plastics and fibers. The thermophysical properties of both initial and modifying additive–containing polysiloxanes, block copolymers, and poleolefins that differ in chemical nature, structure, and composition are analyzed. It is shown that deformation calorimetry allows the simultaneous registration of mechanical (from 5 × 10^?3 kg) and thermal effects (at a sensitivity of 2 × 10^?7 J/s), and the determination of changes in enthalpy, internal energy, and intra- and intermolecular contributions to the formation of the tensile stress response. In other words, it provides a unique opportunity to analyze the deformation mechanism of investigated systems and its dependence on the changing parameters.