Kinetic Substantiation of the Low Activity of Catalysts Based on Isopropanol Solvates of Gadolinium Chloride in the Polymerization of Isoprene

Kinetics and Catalysis - The kinetics was studied for the polymerization of isoprene under the action of a catalyst based on an isopropanol solvate of gadolinium chloride and triisobutylaluminum...     

Polymerization of butadiene on a titanium catalyst in formation of a reaction mixture in turbulent flows

Fundamental aspects of the polymerization of butadiene in the presence of a titanium catalyst under intensive agitation of the reaction mixture in the initial stage of polymerization, provided by use of a tubular turbulent divergent-convergent prereactor, were examined.     

The effect of the disperse composition of a titanium catalyst on the kinetic heterogeneity of isoprene polymerization centers

The kinetic heterogeneity of centers of isoprene polymerization on fractions of titanium catalyst particles is studied. It is found that the isoprene polymerization with a catalyst consisted of particles 0.03–0.14 μm in diameter involves centers of one type with low reactivity. On catalyst particles 0.15–4.50 μm in diameter, the active centers of polymerization of two types with high reactivity may be formed. The addition of modifiers, a reduced temperature of catalyst formation, and the hydrodynamic effect result in the appearance of a narrow fraction of particles 0.15–0.18 μm in diameter with one type of surface active center that generates high-molecular-mass cis-1,4-polyisoprene. The obtained results are in accordance with the concept of particles 0.15–4.50 μm in diameter as aggregates of the elementary crystallites of β-TiCl₃ connected via additional Al-Cl bonds to surface titanium atoms. At the same time, catalyst particles 0.03–0.14 μm in diameter are formed by the minimum number of elementary crystallites, where titanium atoms are bound to a smaller number of chlorine atoms.     

Non-minimal and non-universal supersymmetry

I motivate and discuss non-minimal and non-universal models of supersymmetry and supergravity consistent with string unification at 10¹⁰ GeV.     

The effect of synthesis conditions on the microheterogeneity of the butadiene-isoprene copolymer

The dependence of the microheterogeneity of butadiene-isoprene copolymers synthesized in the presence of a titanium-based catalytic system on the hydrodynamic regime used at the initial moment of formation of the reaction mixture of copolymerization is studied. When copolymers are synthesized with the direct addition of the catalyst to the solution of the comonomers, copolymers featuring a statistical distribution of units are formed, regardless of the composition of the initial comonomer mixture. In this case, the growth of copolymer chains obeys the Bernoulli statistics. Depending of the composition of the initial comonomer mixture, hydrodynamic factors promote different extents of deviation from the statistical growth of copolymer chains.     

Multi-component structure of nonlinear excitations in systems with length-scale competition

We investigate the properties of nonlinear excitations in different types of soliton carrying systems with long-range dispersive interactions. We show that length-scale competition in such systems, universally results in a multi-component structure of nonlinear excitations which may lead to a new type of multistability: coexistence of different nonlinear excitations at the same value of the spectral parameter (i.e., velocity in the case of anharmonic lattices or frequency in nonlinear Schr?dinger models). Received 31 August 2000 and Received in final form 14 December 2000     

Modification of titanium catalytic systems for 1,4-cis-polyisoprene synthesis

The kinetics of isoprene polymerization in an aliphatic solvent on a titanium catalyst modified with n- and π-electron-donor additives, with preliminary single circulation of the reaction mixture through a tubular turbulent apparatus, was studied.     

Enhancement of the activity of the titanium catalyst for isoprene polymerization by improving the step of active site formation

Commercial microheterogeneous titanium catalyst in the step of its preliminary formation was subjected to hydrodynamic action by circulation in a tubular diffuser-confuser apparatus. As a result of such treatment, the Mooney viscosity of the high-molecular-weight polyisoprene prepared in the presence of this catalyst becomes more stable.     

Temporal evolution of the hydrodynamic instability of the boundary between the dense core and the plasma corona during nanosecond explosion of wires

We report the results of investigations of the interaction of a plasma corona with a dense, cold core formed on the discharge axis in the initial stage of the nanosecond electrical explosion of metal wires. The internal structure of the dense core and the dynamics of processes occurring in it were studied by a specially developed method of multi-frame x-ray shadow photography. The large observed amplitudes of the disturbances of the boundary between the dense core and the Z-pinch corona, which are comparable to the core radius, are attributed to the development of Rayleigh-Taylor and Kelvin-Helmholtz hydrodynamic instabilities. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 8, 531–536 (25 April 1998)     

Kinetic nonuniformity of a titanium catalyst in the polymerization of butadiene: Effect of intensifying stirring of the reaction mixture

Intensification of turbulent stirring of the reaction mixture in the course of butadiene polymerization on a titanium catalyst promotes a successive increase in the rate of reaction with increasing polymer content. Independent of the viscosity of the reaction mixture, the concentration of active centers forming the low-molecular-mass fraction of polybutadiene decreases and the molecular mass distribution narrows. The reactivity distribution of active centers is determined by the hydrodynamic effect, and it does not depend on the increasing viscosity of the reaction mixture. This suggests an insignificant influence of viscosity and, hence, diffusion limitations on the distribution of active centers of polymerization over the probability of chain propagation.