Polymer Science, Series A最新文献

Reactor polymer compositions (RPCs) based on UHMWPE with M_w = 1000 kg mol^–1 and low molecular weight HDPE (LMWPE) were studied. Two series of UHMWPE compositions were used to determine the influence of the molecular weight and properties of the LMWPE fraction on the morpho-logy, mechanical and rheological properties of UHMWPE/LMWPE. Сompositions, including from 10 to 80 wt % UHMWPE with M_w = 160 kg mol^–1 (PE-160) were obtained in a two-stage process of ethylene polymerization with a metallocene catalyst. They differed in the order of introduction of PE-160 into UHMWPE (PE-160/UHMWPE and UHMWPE/PE-160). Compositions of UHMWPE and LMWPE with M_w = 48 kg mol^–1 (PE-48/UHMWPE) with PE-48 content from 6 to 30 wt % were synthesized in a single-stage polymerization of ethylene in the presence of a tandem catalyst. A comparison of the shape and size of particles of nascent polymer products was made using the SEM method. The morphology, tensile, dynamic mechanical and rheological properties of RPC have been studied depending on the method of their preparation, the content of the low molecular weight fraction, its molecular weight and physical and mechanical properties. An increase in the proportion of PE-160 and PE-48 in PE-160/UHMWPE and PE‑48/UHMWPE leads to an increase in RPC crystallinity, tensile modulus and dynamic mechanical modulus with significant deviations from the additivity rule.

Anisotropic magnetically active elastomers based on polydimethylsiloxane and magnetic particles of different chemical natures, shapes, and sizes have been synthesized. A comparative analysis of their mechanical properties (elastic modulus, strength, and elongation at break) has been performed depending on the mutual orientation of the internal structure, formed by magnetic filler particles during the synthesis of the composite in a magnetic field, and the direction of the external mechanical force applied to stretch the samples. The anisotropy of mechanical properties is most pronounced in composites based on anisometric particles, needle-like and plate-like. The highest values of anisotropy coefficient of elastic modulus are observed in the composite containing plate-like iron microparticles; for this composite, the ratio of the elastic moduli in the directions parallel and perpendicular to the internal structure reaches a value of five. The use of magnetic filler and its orientation by means of magnetic field is an effective method for creating polymer composites with anisotropy of mechanical properties.

A method for obtaining nonwoven carbon materials by the staged heat treatment of cellulose felt is developed. Fabrics produced from fibrous flax cellulose and viscose fibers by needle punching are used as nonwoven precursors. To obtain carbon fabric precursors the optimum ratios of components are chosen from the data on the formation of nonwoven fabrics and the thermal analysis of various blend formulations. It is shown that the content of flax fibers in the system should be at least 50%. Viscose fibers play the role of a reinforcing material and so far cannot be fully excluded from the system. With an increase in the content of flax cellulose the value of carbon yield grows. The mechanical properties of the carbon felt are provided by the physical network of friction and dispersion contacts between individual fibers. Upon heat treatment of the composite nonwoven material, the morphological features of precursor fibers remain unchanged. The interplanar distances of carbon layers in the carbon material are calculated using X-ray diffraction analysis and transmission electron microscopy. The fraction of carbon upon heat treatment to 1700°С is at least 90%, and after graphitization to 2400°С the purity of the product is above 99%. The maximum values of carbon yield at this temperature may be as high as 25‒27%. The coefficients of thermal conductivity of the carbon felt are measured, and the values obtained are 30% lower than the corresponding parameters of carbon fabrics.

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.

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.