Composites obtained via matrix and pseudo-matrix processes (polymerization and new phase formation)

A variety of composites comprising complexes between macromolecules and growing species such as macromolecules or particles may be prepared using matrix or pseudo-matrix processes. Matrix polycondensation of silica acid in the presence of poly(ethylene glycol) and other polymers in benzene resulting in formation of interpolymer complex (IPC) poly(silica acid)-matrix or composites including the IPC is regarded as an example of matrix processes providing the possibility to synthesize an IPC or composite which cannot be (or hardly may be) obtained by other ways: Theoretical aspects of pseudo-matrix processes in which pseudo-matrix macromolecule recognizes (i.e., forms a complex with) a particle of forming new phase and terminates its subsequent growth are discussed. Experimental data dealing with reduction of Ni(II) in polymer solutions and formation of nano-composites ‘polymer - metallic nickel’ including small particles (3–5 nm in diameter) with narrow size distribution are presented.     

The electret properties of tetrafluoroethylene-hexafluoropropylene copolymer films modified in glow discharge

The electret properties of tetrafluoroethylene-hexafluoropropylene copolymer films modified in direct-current discharge were studied. It was shown that the treatment of the films mounted on the anode had an insignificant effect on the relaxation of negative homocharge despite substantial changes in the chemistry of the surface. However, the low-temperature relaxation process responsible for the instability of the electret state in the untreated film is completely suppressed in the case of decay of positive homocharge. Deep traps associated with high-temperature relaxation processes in the polymer are simultaneously eliminated from the spectrum of surface states.     

Alteration in the surface properties of direct-current discharge-treated tetrafluoroethylene-vinylidene fluoride copolymer films

A change in the contact properties of the surface of tetrafluoroethylene-vinylidene fluoride copolymer films by a dc discharge treatment has been studied, depending on the treatment time and the discharge current. It has been shown that the treatment of the films at the anode and cathode leads to a significant decrease in the contact angle and an increase in the total surface energy and its polar term. The change in the contact properties of the plasma-modified films during storage and heating has been studied as well. The experiments have shown that the formation of polyconjugated structures and crosslinking of macromolecules take place in the film surface layer during long-term treatment at the anode (>60 s, 50 mA), processes that result in an acetone-insoluble layer. The composition and surface structure of the films have been examined by Fourier-transform IR spectroscopy and X-ray photoelectron spectroscopy. The formation of new oxygen-containing groups and double bonds on the polymer surface and crosslinking of macromolecules in the case of anode treatment have been revealed. It has been found experimentally that the discharge treatment increases the peel strength in the Scotch® 810/copolymer film system.     

Exchange interactions and electron delocalization in the mixed-valence cluster V(4)(IV)V(2)(V)O(7)(OC(2)H(5))(12)

The mixed-valence cluster compound V4IVV2VO7(OC2H5)12 was studied by X-band electron paramagnetic resonance (EPR) in the temperature range of 4.2-293 K. According to X-ray diffraction study, the crystal structure of the compound was described by a R3m space group at 295 K (four d1 electrons are equally delocalized on all vanadium ions) and changed to a P21/n space group on cooling the crystals to 173 K (the electrons are preferably localized on the four equatorial vanadium ions). The EPR spectra originate from the S = 1 total spin states with the fine structure averaged to a single Lorentzian line and from the S = 2 total spin states with fine structure partly averaged in the temperature range of 295-200 K and well averaged below 45-50 K. The states of S = 1 and S = 2 of comparable energy (DeltaE approximately 2 cm(-1); ES=1 < ES=2) were shown to be the lowest ones. The VIV <--> VV unpaired electron transfers together with isotropic Heisenberg exchange were shown to determine the total spin states composition and the intracluster dynamics of the compound. Two types of electron transfers were assumed: the single-jump transfer leading to the averaged configurations of the V4IVV2V <--> V3IVVV VIVVV type and to the splitting of the total spin states by intervals comparable in magnitude with the isotropic exchange parameter J approximately 100 cm-1 and the double-jump transfer resulting in dynamics. Temperature dependence of the transition rates nutr was observed. In the range of 295-210 K, the value of nutr = (0.5-0.6) x 10(10) s(-1) is sufficient for averaging the fine structure of the S = 1 states, and below 45 K the value of nutr approximately 1.5 x 10(10) s(-1) also averages the fine structure of the S = 2 state. A change in the localization plane of the VIV ions in the temperature range of 40-50 K was discovered.     

Synthesis of 3-oxoesters and functional derivatives of pyrimidin-4(3<Emphasis Type="Italic">Н</Emphasis>)-one based on 1-(2,6-dihalophenyl)cyclopropan-1-carboxylic acids

Special features of the synthesis and chemical transformations of novel functional derivatives of 6-[1-(2,6-dihalophenyl)cyclopropyl]pyrimidin-4(3H)-one and ethyl esters of 3-[1-(2,6-dihalophenyl)cyclopropyl]-2-methyl-3-oxopropanoic acids prepared from 2-(2,6-dihalophenyl)acetonitriles have been revealed. Novel achiral structural analogs of experimental anti-HIV agent МС-1501 have been synthesized.     

Spin states of Ni3+ ions in PrSrAl1−x Ni x O4 ceramics

Solid solutions PrSrAl_1−x Ni _x O₄ have been synthesized and studied by electron paramagnetic resonance (EPR). It is shown that atx≤0.2 the Ni³⁺ ions may be present both in the high- and low-spin states. Asx increases, the part of high-spin centers increases as well. Models of the paramagnetic centers accounting for micro-heterogeneous structure of these ceramics are proposed. The observed features of the temperature dependence of the EPR signals are explained by the interaction of the nickel ions with fast-relaxing Pr³⁺ ions.     

The reverse shift of the EPR line of paramagnetic centers coupled to species with a fast paramagnetic relaxation

The EPR spectrum of the spin 1/2 paramagnetic centers with a relatively slow relaxation is considered in the case when they are coupled via the Heisenberg exchange interaction to partners which have short times of the longitudinal and transverse paramagnetic relaxation. Under these conditions only the EPR line of paramagnetic centers with a relatively slow relaxation is detectable in experiment. The shape of this line is analyzed by solving numerically kinetic equations for the spin density matrix for simple model systems. Depending on a ratio between the exchange integral and the paramagnetic relaxation rates of partner spins, the EPR line shifts in opposite directions. For moderate relaxation rates, as the relaxation rates decrease, the EPR line shifts toward the gravity center of the total EPR spectrum. In the case of extremely fast relaxation, as the relaxation rates decrease, the reverse shift of the EPR line is expected, the line shifts away from the gravity center of the total EPR spectrum. This type of the non-monotonous line shift was experimentally observed for the monocrystal of [CuNd₂(C₄O₄)₄(H₂O)₁₆] · 2H₂O when relaxation rates were changed by temperature variation.     

About the nature of Ni3+ magnetic centres in the LaSrAl1−xNixO4 ceramics

LaSrAl_1?x Ni _x 0₄ (x≤0.11) ceramics werer studied by EPR. It was established that Ni³⁺ ions in this compound may be in two states: a low spin one with t _2g ⁶ e _g ¹ electron configuration and high spin state with t _2g ⁵ e _g ² electron configuration. It was shown that the random distribution of La³⁺ and Sr²⁺ ions in the heavy metal sublattice leads to two kinds for each type of these centres with different degree of tetragonal distortions. The total concentration of NiO₆ isolated centres in these ceramics does not exceed 5–10 % of a total number of nickel ions at a givenx. A model, explaining these peculiarities observed in an experiment by the enhanced tendency of Ni³⁺ ions to clusterization, was proposed. It appears that even at small concentrations Ni³⁺ ions form clusters and conglomerates, whose structural characteristics of the oxygen octahedra are comparable with those in LaSrNiO₄.