Studying the Dynamics of Hybrid X-Pinches

Since the first experiments with hybrid X-pinches (HXP), it has been shown that a short wire between two conical tungsten electrodes produces the same radiation as a standard X-pinch. Since HXP has a simple construction, it is commonly used in many laboratories instead of standard pinches. Although details of the HXP dynamics remain poorly studied, the main factors governing HXP formation are investigated experimentally in this work. It is shown that the process of the electrode plasma formation is one of the main factors that lead to single hot spot bursts. Experimental results allow the fitting of HXP parameters and determination of the size of the source of X-ray radiation. It is also shown the radiation of HXP can be used as a source for point projection radiography in the wavelength range of soft to hard X-rays. Such sources can be also used for absorption spectroscopy and even electron beams.     

Short-time isoprene polymerization under the action of a titanium–magnesium catalyst

The short-time polymerization of isoprene under the action of a TiCl₄/MgCl2?i-Bu₃Al heterogeneous catalyst has been investigated. Pulse mixing of the catalyst and monomer in a cylindrical tubular reactor with a certain length followed by ethanol injection has made it possible to carry out polymerization for 0.1?0.7 s. In the first 0.3 s, when there is a considerable rise in the activity of the catalyst, living polymerization of isoprene takes place. In this period, polyisoprene has up to 95% trans-1,4 units. Extending the polymerization time to 0.7 s diminishes the average molar mass of polyisoprene, broadens its molar mass distribution, and decreases the concentration of trans-1,4 units to 83%. The data of this study have been analyzed on the basis of the kinetic continuity of the polymer chain initiation and growth.     

Effect of the particle size of the TiCl<Subscript>4</Subscript>-Al<Emphasis Type="Italic">i</Emphasis>-Bu<Subscript>3</Subscript> catalyst on the contribution from mono- and bimetallic active sites to the polymerization of isoprene

The interaction between the coordinatively unsaturated surface of ß-TiCl₃ particles and a liquid phase in the TiCl₄-Ali-Bu₃ catalyst is responsible for the final particle size and the regularities of isoprene polymerization. The correlations of the catalyst activity and the molecular characteristics of polyisoprene with catalyst particle size in the course of catalyst formation and reactivation are indicative of the occurrence of two groups of active sites. “Surface” active sites correspond to the monometallic Cossee model, and they are characterized by low activity and low 1,4-cis specificity in the polymerization of isoprene. “Colloid” active sites have a bimetallic structure and produce polyisoprene at a high rate; the concentration of 1,4-cis units in the resulting polyisoprene is as high as 97%. The contribution from the colloid active sites to the polymerization of isoprene increases with the particle size of ß-TiCl₃.     

Study of plasma parameter’s distribution upon electrical wire explosion

Experimental results on electrical explosion of wires in vacuum with current density  A/m², current rise rate (dI/dt) ~ 50 A/ns and current pulse with amplitude ∼10 kA are presented. The structure of the discharge channels in vacuum has been studied using laser shadow and schlieren imaging with 7 ns frames, UV pinhole images with 5 ns frames and X pinch X-ray backlighting. The information on the dense core material and the conducting plasma distributions was obtained in our experiments by analyzing and comparing the results obtained from all diagnostics.     

Method of composition heterogeneity reduction in copolymer of butadiene with isoprene in ionic coordination polymerization with supported titanium catalysts

Compositional heterogeneity of copolymers of butadiene with isoprene in copolymerization with supported titanium catalyst was investigated. The causes of compositional heterogeneity were found based on solution of an inverse problem of formation of the molecular weight distribution. It was shown that the pre-hydrodynamic effects in a turbulent reactor at the stage of the reaction mixture formation allowed the synthesis of more uniform composition of the copolymer.     

Dynamics of thin exploded-wire plasma with a cold dense core

Ideas are put forward regarding the possibility of a cold dense core, surrounded by a plasma corona, forming near the axis at the initial stage of a nanosecond electric explosion of metal wires, and the influence of such a radial structure on the plasma compression dynamics is discussed. Experimental evidence supporting these suppositions is presented. It includes both indirect confirmations, based on optical and x-ray diagnostics data, and direct observations of the core by new means of x-ray probing employing an X pinch as a source of radiation. Zh. éksp. Teor. Fiz. 114, 1215–1229 (October 1998)     

Structural and kinetic continuum in the butadiene polymerization with titanium catalysts

The short-time polymerization of butadiene induced by heterogeneous titanium catalysts was studied for the first time. In the 0.1?0.3 s time interval, polymerization is characterized by a considerable decrease in the chain propagation rate constant and 1,4-stereospecificity of the catalysts. A structure kinetic continuum model was proposed in which the initiation step and the first propagation steps are kinetically continuous. The violation of this continuity changes the catalyst stereospecificity and creates conditions for chain transfer reactions.     

Kinetic inhomogeneity of copolymerization sites of butadiene and isoprene on titanium catalyst

Copolymerization of butadiene and isoprene on the titanium catalyst proceeds on three types of active sites, and this correspond to the standard set of homopolymerization of isoprene. Sites responsible for the preparation of low-molecular-mass fractions of macromolecules are more active in the copolymerization as compared with homopolymerization of butadiene and isoprene. Change in the hydrodynamic regime in the reaction region is accompanied by an increase in the copolymerization rate due to an increase in the over-all concentration of active sites but it does not affect the typical set of growth sites of macromolecules. Distribution curve of active sites with respect to their reactivity is shifted to the high-molecular-mass region with increasing average weight molecular mass with decreasing average number molecular mass when the corresponding molecular-mass distribution becomes broader.     

Activity of butadiene polymerization centers at in situ formation of titanium catalysts

Directional action on the activity of macromolecule propagation centers and their typical set in synthesis of stereoregular polydienes in the presence of polycentered Ziegler-Natta catalytic systems allows control over the molecular characteristics of the polymers obtained and over the service characteristics of products thereof.