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Dive into the research topics where E. G. Privalko is active.

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Featured researches published by E. G. Privalko.


Polymer | 1998

Influence of chain extenders and chain end groups on properties of segmented polyurethanes. II. Dielectric study

P. Pissis; A. Kanapitsas; Yu.V. Savelyev; E.R. Akhranovich; E. G. Privalko; V. P. Privalko

Abstract Thermally stimulated depolarization currents (TSDC) measurements (temperature range 77–300 K) and broadband a.c. dielectric relaxation spectroscopy (frequency range 10 mHz–2 GHz) were employed to investigate molecular mobility and microphase separation in model segmented polyurethanes (SPUs) from oligotetramethylene glycol 1000, 4,4′-diphenylmethane diisocyanate and different chain extenders. The magnitude of the interfacial Maxwell-Wagner-Sillars (MWS) polarization TSDC peak and of d.c. conductivity have proved to sensitively reflect changes of the degree of microphase separation (DMS). The dielectric strength of both the primary and the secondary transition of the soft segments rich microphase are highest for the SPU with the highest DMS, whereas frequency (temperature) position and shape of the response are not significantly affected by DMS.


Journal of Applied Polymer Science | 1999

Molecular mobility and hydration properties of segmented polyurethanes with varying structure of soft‐ and hard‐chain segments

A. Kanapitsas; P. Pissis; J.L. Gómez Ribelles; M. Monleón Pradas; E. G. Privalko; V. P. Privalko

The molecular mobility and hydration properties of model segmented polyurethanes from either poly(propylene glycol) (PPG) or poly(butylene adipate) (PBAD), both of molecular weight 2000 (soft segments), and three different diisocyanates (all-trans 4,4′-dicyclohexylmethane diisocyanate, 100% t,t HMDI; HMDI with 20% of trans isomers, 20% t,t HMDI; and 4,4′-diphenylmethane diisocyanate, MDI) (hard segments) were investigated using differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) measurements, ac dielectric relaxation spectroscopy (ac DRS), equilibrium water-sorption isotherms (ESI), and dynamic water-sorption isotherms (DSI). No effects of the structure and of the amount of the soft segments on the overall degree of microphase separation (DMS) into microphases rich in soft and hard segments, respectively, were observed. On the contrary, DMS depends on the composition of the diisocyanates used and systematically increases in the order MDI, 20% t,t HMDI, 100% t,t HMDI as indicated by DSC, TSDC, and ac DRS. The PPG-based polyurethanes are characterized by larger values of water content at saturation, h, and smaller values of the diffusion coefficient of water, D. h increases with temperature, indicating that the sorption process is endothermic.


Polymer | 1998

Influence of chain extenders and chain end groups on properties of segmented polyurethanes. I. Phase morphology

Yu.V. Savelyev; E.R. Akhranovich; A. P. Grekov; E. G. Privalko; V.V. Korskanov; V.I. Shtompel; V. P. Privalko; P. Pissis; A. Kanapitsas

Abstract Segmented polyurethanes from oligotetramethylene glycol 1000, 4,4′-diphenylmethane diisocyanate and different chain extenders were characterized by specific heat capacity (temperature interval 130–450 K) and small-angle X-ray scattering measurements. A regular macrolattice of uniform-size micro-domains of stiff segments spanning a continuous matrix of soft segments was observed for the sample chain-extended with dihydrazide of isophthalipc acid, DIPA. The distribution of microdomains by sizes remained unchanged, whereas the overall degree of micropahase separation (DMS) increased due to dilution of DIPA and/or blocking of chain ends with crown ether-containing di- and monohydrazides. The distribution of microdomains by sizes broadened, whereas the DMS either remained unchanged or slightly decreased on dilution of DIPA with hydroxyl-containing chain extenders [1,4-di-N-oxy-2,3-bis-(oxymethyl)-quinoxaline and 1,4-butane-diol, respectively].


Journal of Physics: Conference Series | 2005

Polyimide/silica nanocomposites with low values of dielectric permittivity

Daniel Fragiadakis; E Logakis; P. Pissis; V Yu Kramarenko; T A Shantalii; Iryna L. Karpova; Kateryna S. Dragan; E. G. Privalko; A A Usenko; V. P. Privalko

Polyimide nanocomposites prepared by the in situ generation of crosslinked organosilicon nanophase by sol-gel techniques were investigated by dielectric relaxation spectroscopy, themally stimulated depolarization currents and dynamic mechanical analysis. Two series of samples were investigated with molar mass 5000 and 10000 of the polyimide chains. In both series a non-additive decrease of the dielectric permittivity with increasing amount of filler was observed, indicating a loose inner structure of the spatial aggregates of the organosilicon nanophase. The magnitude of the dielectric γ relaxation of polyimide was found to increase with increasing filler content for the shorter chains, whereas the opposite was observed for the longer ones.


European Polymer Journal | 1999

Dielectric studies of molecular mobility and microphase separation in segmented polyurethanes

G. Georgoussis; A. Kyritsis; P. Pissis; Yu.V. Savelyev; E.R. Akhranovich; E. G. Privalko; V. P. Privalko

Abstract This work deals with molecular mobility and microphase separation studies on segmented polyurethanes with different fragments, including crown ethers, as chain extenders and/or chain end groups. The techniques used include thermally stimulated depolarization current (TSDC) in the temperature range −185°–30°C and broadband dielectric relaxation spectroscopy (DRS) in the frequency and temperature ranges of 10 −2 –10 6 Hz and −55°–80°C. The combination of these techniques allowed the secondary γ and β mechanisms, the primary α mechanism, the Maxwell–Wagner–Sillars (MWS) mechanism associated with interfacial polarization and dc conductivity σ dc to be recorded. The results suggest that addition of crown ethers promotes microphase separation. Specific characteristics of the primary α and the MWS relaxations and σ dc were found to systematically change with the degree of microphase separation. They should be further quantified and tested on selected systems.


Science and Technology of Advanced Materials | 2003

Synthesis and thermomechanical characterization of polyimides reinforced with the sol?gel derived nanoparticles

Tatiana A. Shantalii; Iryna L. Karpova; Kateryna S. Dragan; E. G. Privalko; V. P. Privalko

Abstract Polyimide-based nanocomposites prepared by the in situ generation of inorganic nanoparticles (silica) through the sol–gel process were characterized by kinetics of water uptake, ther mogravimetry and dynamic mechanical analysis. Silica particles turned out to possess a rather loose inner structure characterized by enhanced water diffusivities andby dynamic elasticity moduli comparable to that of the pristine, glassy PI. Thermal stability and thermomechanical properties of nano composites in the glassy state remained nearly the same as those of the pristine PI, while a significant reinforcement effect was observed for the rubbery PI matrix.


Science and Technology of Advanced Materials | 2002

Viscoelasticity and flow behavior of irradiation grafted nano-inorganic particle filled polypropylene composites in the melt state

V. P. Privalko; V.F. Shumsky; E. G. Privalko; V.M. Karaman; R. Walter; K. Friedrich; M.Q. Zhang; M.Z. Rong

Abstract Nanoparticles (mean size about 7 nm) of the standard pyrogenic Aerosil 1380 (Degussa) pregrafted by γ-irradiation with styrene were melt-compounded with the general purpose isotactic polypropylene homopolymer to prepare four nanocomposites with filler volume contents up to 4.68%. Storage G′(ω) and loss G″(ω) shear moduli in the melt state (measured in the range of linear viscoelasticity at three temperatures in the frequency window spanning about three decades) were treated to derive the relaxation times spectra h(τ) using the nlreg computer program based on Tikhonov’s method of non-linear regularization. The experimental data were interpreted in terms of the tentative model highlighting the structural significance of the ratio of mean thickness of polymer interlayer between neighboring filler particles, 〈L〉, to the mean radius of gyration of a polymer coil, 〈Rg〉. In the range of very low filler loadings characterized by large scaled distances, 〈L〉/〈Rg〉 ≥ 1, all nanocomposites behaved as Newtonian liquids in which the self-diffusion of macromolecular coils was, however, slowed down. The onset of plastic yield phenomenon for a nanocomposite with the filler volume content as low as 4.68% was regarded as the experimental evidence for the shear-resistant, infinite cluster of filler particles coated with polymer boundary interphase when the scaled distance approached the ‘critical’ value, 〈L〉/〈Rg〉 ≤ 1.


European Polymer Journal | 2003

Phase morphology and molecular dynamics of a polyurethane ionomer reinforced with a liquid crystalline filler

A.G. Charnetskaya; G. Polizos; V. I. Shtompel; E. G. Privalko; Yu. Yu. Kercha; P. Pissis

Solution-blended binary composites of ionic segmented polyurethane (SPU-I) and liquid crystalline oligomer (LCO) were characterized by wide-angle (WAXS) and small-angle (SAXS) X-ray scattering, differential scanning calorimetry (DSC), thermally stimulated depolarization currents (TSDC) and dielectric relaxation spectroscopy (DRS). Both components mutually influenced their states of aggregation in blends (most significantly, promoting smearingout of interfaces between stiff and soft chain fragments of SPU-I into broad interfacial regions of intermediate composition). Apparently, the blend with w ¼ 0:10 happened to be most favorable for crystallization of the LCO, while the degree of microphase separation for SPU-I became lower and the distribution of stiff domains by sizes became broader, the higher the LCO content. The overall molecular mobility of SPU-I in blends was significantly reduced. This reduction included the intensity of the secondary and the primary relaxations, and of the interfacial Maxwell–Wagner– Sillars (MWS) relaxation, whereas the transition temperatures remained essentially composition-invariant. The Arrhenius-like behavior for the dc conductivity concomitant to the non-Arrhenius (i.e., Vogel–Tammann–Fulcher) frequency dependence for the a relaxation in blends suggested a decoupling of conductivity from the motion of the SPU-I soft chain segments. � 2003 Elsevier Ltd. All rights reserved.


Journal of Materials Science | 1999

Composition-dependent properties of polyethylene/kaolin composites. Part II : Thermoelastic behaviour of blow-moulded samples

V. P. Privalko; D.I. Balta Calleja; D. I. Sukhorukov; E. G. Privalko; R. Walter; Klaus Friedrich

Samples of the blow-moulding grade HDPE filled with Kaolin were characterized by wide-angle X-ray scattering, microhardness and stretching calorimetry techniques. It is shown that crystallinity of the polymer matrix in the filled samples remains essentially the same as that in the neat polymer regardless of the filler content. The thermoelastic behaviour of all samples below the apparent yield point ∈* is quantitatively described by classical equations for elastic solids. The thermoelastic parameters of the boundary interphase (BI) are discussed in terms of predictions of the step-by-step averaging approach. The experimental values of the internal energy increment in the inelastic strain interval for unfilled and filled samples are analyzed in the light of the filler debonding processes in the latter.


Journal of Applied Polymer Science | 1999

Structure–property relationships in thermoplastic-apparent interpenetrating polymer networks based on crystallizable polyurethane and styrene–acrylic acid copolymer

A. Kyritsis; P. Pissis; O. P. Grigorieva; L. M. Sergeeva; A. A. Brouko; O. N. Zimich; E. G. Privalko; V. I. Shtompel; V. P. Privalko

Structure-property relationships in thermoplastic-apparent interpenetrating polymer networks (t-AIPNs), prepared by mechanical blending in a common solvent of crystallizable polyurethane (CPU) and styrene/acrylic acid random copolymer (S/AA), were investigated by means of wide-angle and small-angle X-ray scattering (WAXS and SAXS), dynamic mechanical analysis (DMA), thermally stimulated depolarization currents (TSDC) techniques, dielectric relaxation spectroscopy (DRS), and density, water uptake, deformation, and strength characteristics measurements. Several mechanical and dielectric relaxations of the pure components were characterized, and the effects thereupon induced by blending were followed. The two components show weak affinity to each other. The t-AIPNs can be classified into two groups with high and low contents of CPU, showing essentially the behavior of CPU and of S/AA, respectively. On the other hand, deviations from additivity in several properties indicate interactions between the two components, caused by the formation of H-bonds between their functional groups, and resulting in partial miscibility. In addition, significant changes are observed on some properties of the t-AIPNs on addition of small amounts of either of the components.

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V. P. Privalko

National Academy of Sciences of Ukraine

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P. Pissis

National Technical University of Athens

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K. Friedrich

Kaiserslautern University of Technology

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R. V. Dinzhos

National Academy of Sciences of Ukraine

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Sergiy M. Ponomarenko

National Academy of Sciences of Ukraine

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Tatiana A. Shantalii

National Academy of Sciences of Ukraine

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Vitaly M. Karaman

National Academy of Sciences of Ukraine

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R. Walter

Kaiserslautern University of Technology

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Iryna L. Karpova

National Academy of Sciences of Ukraine

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Kateryna S. Dragan

National Academy of Sciences of Ukraine

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