Polymer Science, Series A最新文献

The composite samples with the graphene filler content of 0.014 to 0.05 wt % have been prepared via the in situ polymerization. The effect of the ultralow content of graphene on the set of wear-resistant and tribological properties of the synthesized composited based on ultra-high molecular weight polyethylene has been studied. Weas resistance of the synthesized materials under conditions of high-speed impact of a water-sand suspension, wear during microcutting and friction wear resistance have been investigated. Furthermore, the friction coefficient on steel has been determined. The introduction of graphene into the ultra-high molecular weight polyethylene has improved the resistance to abrasion during microcutting and has increased the wear resistance under the action of the water-sand suspension (the free abrasive wear).

Most commercial polyacrylonitrile-based carbon fibers are microfibers derived from the wet-spinning or dry-jet wet-spinning polyacrylonitrile fiber. Nano carbon fibers made by electrospinning and post-processing have many advantages over micro carbon fibers in performance, but the research on nano carbon fibers is far from enough. In this work, polyacrylonitrile-based nano- and microfibers obtained by electrospinning and dry-jet wet spinning are converted into nano- and micro carbon fibers under the same pre-oxidation and carbonization conditions. The evolution of morphology, elemental content, functional groups and apparent crystallinity of the two size-scale fibers before and after carbonization are studied. The relationship between their structure and their electrical property is speculated. The results show that pre-oxidized nano fibers’ absorption of visible light is much weaker than microfibers. The oxygen content of the pre-oxidized nanofibers is higher, and the carbon content in the carbonization process is always higher than that of microfibers. The nanofibers are more accessible to crystallize than microfibers. They can obtain better electrical properties than microfibers and have a more excellent application prospect as conductive fillers in antistatic composites.

The binding of the biologically active natural dye curcumin by star-shaped poly-2-alkyl-2-oxazolines of various structures in an aqueous medium has been studied by spectrophotometry in the ultraviolet and visible regions. The objects of study were synthesized and previously described four- and eight-armed star-shaped poly-2-alkyl-2-oxazolines with calixarene central units. The Benesi–Hildebrand method was used to determine the binding constants of dye molecules by polymer micelles. The results obtained demonstrate highly efficient binding of curcumin by polymer macromolecules and micelles in aqueous solutions. It has been shown that the efficiency of curcumin binding by star polyoxazolines is determined to a greater extent by the structure of the hydrophobic calixarene central unit, rather than the nature of polyoxazoline arms.

A series of novel anionic block copolymers, in which the neutral block is formed by 2-phenylethyl methacrylate (PEM) and the ionic block is prepared via statistical copolymerization of lithium 1-[3-(methacryloyloxy)-propylsulfonyl]-1-(trifluoromethanesulfonyl)imide (LiM) and methyl ether of poly(ethylene glycol) methacrylate (PEGM) have been synthesized. The effects of chemical structure, composition, and molecular mass of the blocks on ionic conductivity and thermal properties of the poly[PEM–block–(LiM–stat–PEGM)] block copolymers have been investigated. It has been found by means of small-angle X-ray scattering that the introduction of a small fraction of the lithium-containing units (~7 mol %) in the structure of neutral poly[PEM–block–PEGM] copolymer leads to microphase separation and ordering of the system. Combined small-angle X-ray scattering and atomic force microscopy data have evidenced the formation of lamellar structure with the interplanar distance of d ~ 28 nm.

The process of complex formation between polyethylenimine and copper cations in an aqueous solution, followed by isolation of copper nanoparticles, has been studied by means of ESR spectroscopy. It has been shown that in excess of the polymer in the solution the copper cation forms complex containing three nitrogen atoms in the coordination sphere, with distorted tetragonal geometry. The increase in copper concentration has led to the formation of the copper cation complex with water. Addition of the reducing agent NaBH₄ to the studied solutions has led to the formation of copper nanoparticles accompanied by gradual disappearance of the ESR signal of Cu(II) and the appearance of the ESR signal typical of the mononuclear copper complexes with polyethylenimine.

The structure and phase transitions in the hydroxypropyl cellulose–mixed solvent water/ethanol system upon heating are studied. As the content of ethanol in the mixed solvent is increased, hydroxypropyl cellulose solutions undergo phase separation at higher temperatures. At the ethanol content above 50% there is no phase separation in the system upon heating to 400 К. The sizes of macromolecular associates in solutions are determined by the turbidity spectrum method.

Structure formation during deformation of a mixture of melts of a thermoplastic polymer (polysulfone) and a liquid crystal polymer has been investigated by means of analytical scanning electron microscopy. Viscosity of the LC polymer at high shear rate has been significantly lower in comparison with the thermoplastic. The experiment has been performed at controlled volume flow under conditions of flow through a capillary at a high and low deformation rate. The principal result of the observations has been the statement of self-organization effect manifested as the phase separation and formation of the regions with the increased concentration of the LC polymer in the thermoplastic matrix. Such system has been an emulsion, and a conical converging flow has been formed at the transition from the wide cylinder of the capillary viscometer to a narrow capillary installed at its bottom. Such geometry of deformation has led to the appearance of a longitudinal flow with the formation of jets (fibers) in the extrudate bulk and the surface layer of the liquid crystal polymer. Effective viscosity of the mixture has been lowered in comparison with this of the thermoplastic, due to self-assembly of the LC polymer.

This contribution is focused on the examination of adsorption/desorptiom isotherms for nitrogen at 77 K and benzene vapors at 293 K on various hypercrosslinked polystyrene (HP) resins. All isotherms for N₂ are identical in their shapes and are characterized by a steep rise of the adsorption branch at low p/p₀ followed by a less steep hoisting of the branch with increasing relative pressure. Adsorption isotherm for benzene demonstrates an ill-defined convex initial part followed by a significant rise in network loading with further increase in relative pressure. In the both cases we assume the rise in adsorption to reflect the relaxation of inner stresses with the simultaneous increase in the volume of networks. The distinction between the two types of isotherms is conditioned upon the fact that in the networks cooled down to 77 K stresses are stronger and the initial volume of the sample is more compressed. The amounts of nitrogen and benzene absorbed at relative pressure of 0.95 are the same order of magnitude, indicating similar swelling of HP in the both adsorbates. The adsorption behaviors of hypercrosslinked PIM-type polymers are governed by the same effects.

Effect of the structure of synthetic polyacids on the formation and properties of their interpolymer complexes with sodium alginate is investigated. The hydrogels was shown to be predominantly formed via hydrogen bonds, with their type depending on the structure of polyacid and the amount of bound water. Study of the behavior of the hydrogels in water and phosphate-buffed saline with рН 7.2 demonstrates that the properties of the hydrogels are influenced by the ratio of components and the treatment temperature, in addition to the nature of polyacid. The possibility of using hydrogels as a basis for drug delivery systems is examined by the example of preparation lidocaine.