Relaxation spectroscopy of LC main chain polymers: Experimental and theoretical investigations

A series of thermotropic main chain polymers with extended dimethylsiloxane segments was investigated. The study of dielectric properties of polymers revealed the relationship between their ability to form a mesophase and their molecular mobility. The peculiar behaviour of dielectric α-relaxation parameters during the transition from mesomorphic to isotropic members of this polymeric series was shown. The theoretical approaches were developed for understanding macrochain dynamics of liquid crystalline polymers. The theoretical and experimental results are in good agreement.     

Synthesis and properties of super high molecular weight polyhexene-1

TiCl₄–alkylaluminium systems have been fixed on graphite and other inorganic supports and used in hexene-1 polymerization. Kinetic studies show a decreasing polymerization rate from high initial values. High conversions (up to 99%) are reached, although retardation by a diffusion process is observed above 60%. The polymers have high molecular weights (up to 10⁷) and high isotacticity (up to 98.5% from ¹³C NMR analysis). The effects of the nature of the components (carrier, alkylaluminium), and their concentration on the polymerization kinetics and the molecular structure of the polymer are discussed. The linear chain has one alkyl group (the alkylaluminium) and one unsaturation as the chain ends. Despite the high tacticity, the polymers are amorphous and rubber-like.     

Synthesis of polyolefin composition in the presence of supported catalysts

Polyolefins are basic materials in the plastics. Their application is limited by their low thermostability, adhesion, hardness and other physico-mechanical properties. The following treatments are known to improve and modify polyolefin properties: the incorporation of inorganic or organic fillers with a greater hardness and rigidity into the polyolefin matrix, the grafting of functional groups to polyolefins, and crosslinking with the formation of a network structure in the polyolefin matrix. In the case of polymers and inorganic materials, the activation of their surface by the functionalizing and fixing of transition metals allows one to perform polymerization of monomers on a surface to obtain a polymer–polymer composites and a highly filled polymer–inorganic composites.     

Phase diagram and high-pressure boundary of hydrate formation in the ethane-water system

Dissociation temperatures of gas hydrate formed in the ethane-water system were studied at pressures up to 1500 MPa. In situ neutron diffraction analysis and X-ray diffraction analysis in a diamond anvil cell showed that the gas hydrate formed in the ethane-water system at 340, 700, and 1840 MPa and room temperature belongs to the cubic structure I (CS-I). Raman spectra of C-C vibrations of ethane molecules in the hydrate phase, as well as the spectra of solid and liquid ethane under high-pressure conditions were studied at pressures up to 6900 MPa. Within 170-3600 MPa Raman shift of the C-C vibration mode of ethane in the hydrate phase did not show any discontinuities, which could be evidence of possible phase transformations. The upper pressure boundary of high-pressure hydrate existence was discovered at the pressure of 3600 MPa. This boundary corresponds to decomposition of the hydrate to solid ethane and ice VII. The type of phase diagram of ethane-water system was proposed in the pressure range of hydrate formation (0-3600 MPa).     

Lattice model theory of chain stiffening and relaxation properties of macromolecules in the nematic LC state

The relaxation properties of polymer chains In the nematic LC-state or in the external quadrupole field may depend both on the variation of the conformation in the ordered state and on the activation barrier of the molecular (or external) field. This barrier should be surmounted during reorientation of chain elements. The lattice model theory of chain stiffening of macromolecules in the LC-state is proposed. The calculation and comparison of the longitudinal and transversal relaxation spectra for the continuous and discrete rotameric mechanism of the mobility are performed. For the simplest model of a heterogeneous polymer chain the possibility of the more complex relaxational behavior i.e. the existence of two longitudinal and two transversal relaxation spectra was shown.     

Kinetics of the polarization transfer in spatially disordered spin systems: Depolarization of impurity beta-active nuclei

We performed theoretical and experimental studies of the delocalization of the nuclear polarization of impurity beta-active nuclei ⁸Li in the spatially disordered system of ⁶Li nuclei in LiF single crystals. The process is controlled by the dipole-dipole interaction of nuclear magnetic moments with other nuclei (⁷Li, ¹⁹F) in the crystal. It is effective in a wide range of magnetic fields H ₀ = 150–3000 G as a result of a unique proximity of the g-factors of ⁸Li and ⁶Li nuclei: (g(⁸Li) − g(⁶Li))/g(⁶Li) = 0.0057. The kinetics of the ⁸Li depolarization is measured for an ⁶Li concentration of 0.15%–10.06% and in the field H ₀ of 200, 692 and 1210 G. A satisfactory explanation of the results is obtained on the basis of a numerical-analytical simulation of the process.     

Model theory of relaxation properties of macromolecules in the nematic LC state

The continuous and lattice dynamic models of the macromolecules in the LC state are considered. The relaxation properties of polymer chain in the nematic LC state may depend on both the variation of the conformation in the ordered state and on the activation barrier of the molecular field. The calculation and comparison of the longitudinal and transversal relaxation spectra for the continuous and discrete rotameric mechanism of the mobility are performed. For the simplest model of the heterogeneous polymer chain for continuous dynamic models the complicated relaxational behavior with two longitudinal and two transversal branches is manifested. The dynamic properties of the lattice dynamic model with spacer consisting of several bonds are considered.     

Study of ionic catalytic systems by the electrodialysis method

A special method of electrodialysis has been developed for investigation of the kinetics and mechanism of polymerization reactions involving ions. The ionic composition of homogeneous systems such as Cp₂TiRClAlRCl₂, RTiCl₃ + AlRCl₂, Ti(OR)₄ + AlR₃, and (RLi)_n has been studied. The composition of catalytically active ions has been determined. Using the regularities of “open” systems, the methods of determining the carbocation reactivity under electrodialysis conditions havebeen worked out. The impulse electrodialysis method has been suggested for studying ionic polymerization kinetics and evaluating the rate constants ofion reactions with the monomer and gegenion.