Ethylene polymerization with homogeneous and heterogeneous catalysts based on bis(4‐fluorophenyl)methyl‐substituted bis(imino)pyridyliron complexes

A series of bis(4‐fluorophenyl)methyl‐substituted bis(imino)pyridyliron chloride complexes were immobilized on oxide supports. The kinetics of ethylene polymerization by both homogeneous and heterogeneous systems was followed, the catalysts mostly demonstrating high activities. The effect of the ligands nature and reaction conditions on the catalytic activities and molecular weights of the resultant polyethylenes was examined. In contrast to homogeneous systems, the supported iron complexes were found to exhibit high and stable activity upon activation with triisobutyl aluminium, producing high‐molecular‐weight polyethylene with good morphology. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42674.     

Abrasive-jet machining of large hollow components

Analytical formulas are derived for the internal surface characteristics of a large cylindrical workpiece after treatment by an abrasive–air jet as a function of the machining conditions. A formula for the productivity is also presented.     

High-Strength Weldable Alloy 1970 Based on the Al - Zn - Mg System

In the 1980s researchers of the All-Russia Institute of Light Alloys and the “Komposit” Research and Production Association developed a high-strength weldable corrosion-resistant alloy based on the Al - Zn - Mg - Cu - Sc - Zr system. The alloy was graded 1970 and used for fabricating pilot batches of sheets, plates, sections, and pressed preforms. Results of studies of the structure and properties of these semiproducts and their welded joints are presented. Alloy 1970 was initially designed for the purpose of spacecraft engineering. In recent years the aircraft industry has shown interest in high-strength weldable alloys for this purposes. Sheets from alloy 1970 were studied from the standpoint of their applicability as an aircraft material.__________Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 4, pp. 10 – 17, April, 2005.     

Thermal activation currents of biocompatible nanocrystalline calcium hydroxyapatite Ca<Subscript>10</Subscript>(PO<Subscript>4</Subscript>)<Subscript>6</Subscript>(OH)<Subscript>2</Subscript>

Nanocrystalline stoiochiometric calcium hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (NCHA), a counterpart of the inorganic osseous tissue component, is synthesized under biomimetic conditions. Methods of physico-chemical analysis (XRD, IRS, derivatography, DSC, ESCA, SEM, TEM) are used to identify the products of synthesis. The temperature dependence of thermally stimulated currents (TSCs) of NCHA is studied in the temperature range of 300–600 K and the effect of the dispersion degree on TSCs is analyzed.     

Change of the wear resistance of a superhigh-molecular-weight polyethylene plate upon its modification by a mechanically activated ceramic nanopowder

The object of investigation is superhigh-molecular-weght polyethylene (SMWP) with a molecular weight of up to 8 × 10⁶ g/mole and a particle size from 63 to 315 μm obtained by the technique developed at the Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences. The purpose of this work is to create structural polymer materials with high physical and technical characteristics and to extend the scope of the application of this polymer in industry. The problem is solved by the modification of SMWP powder particles via the introduction of nanodispersed ceramic materials. Based on the data obtained, the methods of the production of the article samples from nanocomposite materials based on SMWP via the hot-pressing technique were developed and the influence of the nanomodifiers on the properties of the composite material was studied.     

The kinetic evidence for the formation of multiple active species in a bis(phenoxy-imine) zirconium dichloride/MAO catalyst during ethylene polymerization

The effects of polymerization time and temperature on the molecular weight and molecular weight distribution of polyethylene, produced over homogeneous catalyst bis[N-(3-tert-butyl salicylidene)anilinato]zirconium(IV) dichloride ^tBu-L₂ZrCl₂/MAO have been studied. The data on the number of active centers (C_P) and propagation rate constants (k_P) at different polymerization time have been obtained as well. It was found that at a short polymerization time two types of active centers, producing low molecular weight PE (M_w = (4-10) × 10³ g mol⁻¹) are formed. The number of these centers was estimated to be 11% of total zirconium complex and their reactivity is very high (the k_P value was found to be 54 × 10³ L mol⁻¹ s⁻¹ at 35 °C). High initial activity of the catalyst fell with the increase in polymerization time, whereas the polydispersity values of the resulting PE increase due to formation of new centers, producing high molecular weight PE (M_w = (30-1300) × 10³ g mol⁻¹). It was found that the decrease in activity is caused by reducing the initial active centers number and lower reactivity of the new-formed centers (k_P = 17 × 10³ L mol⁻¹ s⁻¹).     

Hydrogen effect on the molecular weight distribution of polymers obtained by polymerization of ethylene and α-olefins over supported titanium-magnesium catalysts

Comparative data on the molecular weight distribution of polymers obtained by polymerization of ethylene, propylene and 1-hexene, and copolymerization of ethylene with α-olefins over the titanium-magnesium catalysts (TMC) in the absence and presence of hydrogen are presented. In contrast to the ethylene polymerization, in the cases of propylene and 1-hexene polymerization and copolymerization of ethylene with α-olefins, the hydrogen addition is characterized by noticeable narrowing of the molecular weight distribution (MWD) due to lower contribution of the MWD component with high molecular weight. This result is an evidence of the increased reactivity of TMC active sites producing high molecular weight poly-α-olefins and copolymers of ethylene with α-olefins in the chain transfer reaction with hydrogen. It is suggested that the increased reactivity of these sites in the transfer reaction with hydrogen appears after the 2,1-addition of α-olefin to the growing polymer chain.