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  • 1
    Electronic Resource
    Electronic Resource
    Thermal, Dynamic Mechanical and Dielectric Behavior of Liquid-Crystalline Linear and Crosslinked Polyurethanes with Mesogenic Group in Side Chains (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 518 (July 2006), p. 367-374 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: This paper describes DSC, dielectric and dynamic mechanical behavior of linear andcrosslinked liquid crystalline (LC) polyurethanes based on LC diols with a mesogenic group in theside chain, diisocyanates of various flexibility and two triols. From our investigations it follows: a)Linear polymers prepared from diols with simple end side chain substituents (as hydrogen, nitro andnitril group) exhibit only amorphous behavior regardless of the structure of used diisocyanate;generally, the most pronounced LC behavior exhibited polymers prepared from a diol with phenylsubstituent. b) Investigation of the curing reaction showed that rheological power-law parameters,which are characteristic of the structure at the gel point, are dependent on the initial ratio of thereactants (amount of LC diol in EANCs). c) Strong physical interactions between the mesogenssupport the cyclization in the course of crosslinking reaction. d) Introduction of chemical junctions(amount of triols) suppresses LC ordering in the networks
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/13/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.518.367.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Dielectric properties of fluorocarbon and chlorofluorocarbon films plasma polymerized in an R.F. glow discharge
    Amsterdam : Elsevier
    Thin Solid Films 136 (1986), S. 11-19 
    Details
    ISSN: 0040-6090
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0040-6090(86)90103-3
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  • 3
    Electronic Resource
    Electronic Resource
    Dielectric behaviour of swollen poly(acrylamide) gels in the collapse region (1987)
    Springer
    Polymer bulletin 18 (1987), S. 81-86 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The dielectrical behaviour (in the frequency range f=20 Hz — 200 kHz) of two networks — polyacrylamide (PAAm) network and a network obtained by the copolymerization of acrylamide with 3 mol.% sodium methacrylate (MNa) in a mixed solvent deionized water — acetone (acetone concentration a=0–80 vol.%) at T=298 K and pH ∼ 7 was investigated. High values of complex permitivity ɛx(=ɛ′+iɛ″) were found for both networks. For the PAAm network the dependence of both components of ɛx on a is continuous. On the other hand, for the ionized network the jumpwise decrease in swelling at the phase transition is accompanied by a jumpwise increase in the values of both components of ɛx at all frequencies; the critical concentration of acetone a at the collapse is frequency independent. The high values of components of ɛx and their dependences on a observed with both networks can be explained qualitatively by the polarization of the space charge in the measured samples. While with the PAAm network the charge is given by the dissociation of water, in the case of the P(AAm-MNa) network ions arising by the dissociation of MNa also contribute to this charge. The collapse in the ionized network is accompanied by a jumpwise increase in the effective charge concentration in the gel. The fact that the extent of the jumpwise change of components of ɛx in the collapse is frequency dependent suggests that the dependence of ɛx on a is also affected by the mobility of charge carriers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00255826
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  • 4
    Electronic Resource
    Electronic Resource
    The relaxation and equilibrium behaviour of model polyurethane networks (1980)
    Springer
    Polymer bulletin 3 (1980), S. 497-503 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The mechanical, dielectric and rheo-optical behaviour of model networks prepared from OH-terminated poly(oxypropylene)triols and 4,4′-diphenylmethane diisocyanate with various molar ratios of hydroxyl to isocyanate groups, rH=0.95 to 1.7, was investigated. The observed independence of the stress-optical coefficient of rH indicates the homogeneity of networks. Networks prepared with rH≈1 exhibit a narrow transition zone indicating a narrow chain distribution. With increasing rh, the transition becomes distinctly broader; dielectric measurements are well correlated with the mechanical ones. The equilibrium modulus markedly decreases with increasing rH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00283826
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  • 5
    Electronic Resource
    Electronic Resource
    Violation of the power-law dynamic mechanical behaviour at the gel point threshold in non-stoichiometric epoxide systems (1999)
    Springer
    Polymer bulletin 42 (1999), S. 465-472 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary The dynamic mechanical behaviour of fully cured off-stoichiometric epoxy systems prepared from poly(oxypropylene)diamine (Jeff D-400) or -triamine (Jeff T-403) and diglycidyl ether of Bisphenol A (DGEBA) with initial ratios of reactive amine (NH2) and epoxide (E) groups, r H= (2[NH2])/[E] ranging from 2.4 to 4.3 was investigated in the gelation threshold region. The evolution of the dynamic behaviour of two stoichiometric samples with r H= 1 with reaction time, t r , was also studied. The critical ratios for gelation, r c H, of fully cured samples were determined from extraction experiments (r c H= 2.54 for Jeff D-400/DGEBA and r c H= 4.15 for Jeff T-403/DGEBA systems, respectively). For both stoichiometric critical gel (CG) structures obtained by changing the curing time t r , a power-law rheological behaviour (G′∼ G″∼ωn, G′ and G″ are the storage and loss moduli, respectively, ω is angular frequency and n is a critical exponent) with the loss tangent, tan δ= G″/G′ independent of frequency, was found. On the other hand, both CG off-stoichiometric systems with r c H ratios show a small dependence of tan δ on ω, so that the critical power-law behaviour is not exactly obeyed. More complex CG structure in these samples, formed due to differences in the structure growth process, was suggested to account for violation of the power-law behaviour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890050490
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  • 6
    Electronic Resource
    Electronic Resource
    The high temperature dispersion in rubbers (1981)
    Springer
    Polymer bulletin 4 (1981), S. 399-405 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Results obtained by measuring dielectric absorption spectra in a 10−3 up to 107 Hz frequency region as well as depolarisation currents, showing the existence of a high-temperature maximum in both natural and synthetic cis-1, 4-polyisoprene, are given. The influence exerted by the network density and the degree of quenching of the sample upon this maximum is explained by the orientation of the microblock arrangements in the polymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00254971
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  • 7
    Electronic Resource
    Electronic Resource
    Dielectric and mechanical behaviour of polyurethane networks from poly(oxypropylene)diols or-triols and diisocyanate (1996)
    Springer
    Polymer bulletin 36 (1996), S. 233-239 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Thermally stimulated depolarization currents and dielectric and dynamic mechanical behaviour of polyurethane networks prepared from poly(oxypropylene)diols or-triols and 4,4-diphenylmethane diisocyanate were studied. While the frequency and temperature positions of mechanical and dielectric functions are predominantly determined by the concentration of polar urethane groups in the network chain, the equilibrium modulus correlates with network chain length. The effect of the chain polarity on the shape of loss permittivity vs. frequency curves is more pronounced in the low frequency region than in the high frequency one and is practically the same for stoichiometric and off-stoichiometric networks measured earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00294912
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of interphase interactions on the dielectric behaviour of polycarbonate/poly(styrene-co-acrylonitrile) blends (2000)
    Springer
    Polymer bulletin 44 (2000), S. 555-562 
    Details
    ISSN: 1436-2449
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Summary Frequency and temperature dependences of the complex permittivity ɛ* (=ɛ′−i ɛ″, ɛ′ is the real and ɛ″ imaginary component, respectively) were investigated for blends of polycarbonate/poly(styrene-co-acrylonitrile) (PC/SAN). In the blends, two α-processes corresponding to the main transitions of PC and SAN were found; for SAN at concentrations c SAN≥ 20 wt% and for PC for c PC≥ 40 wt%. The Havriliak-Negami shape parameters describing the frequency dependence of ɛ′ and ɛ″ are virtually independent of temperature and composition. Slight shift of temperature or frequency positions of α-processes found for blends from those found for neat polymers with composition of blends indicated partial miscibility of components. The concentration dependences of ɛ′ and ɛ″ at low frequencies and high temperatures could be described with the Böttcher equation from which it followed that percolation threshold takes place for SAN inclusions at c SAN≈ 30 wt%. Both the reduced dielectric strength ΔɛT and the reduced Onsager term O t/c SAN (or O t/c PC) in dependence on the blend composition could be qualitatively described by the Böttcher equation as well.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002890070078
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  • 9
    Electronic Resource
    Electronic Resource
    Viscoelastic behaviour of model polyurethane networks in the main transition zone (1987)
    Springer
    Colloid & polymer science 265 (1987), S. 8-18 
    Details
    ISSN: 1435-1536
    Keywords: Mechanical measurements ; model networks ; glass relaxation ; unperfect crosslinking reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Starlike poly (oxypropylene) molecules (M=2630 resp. 710 g/mol), each with three OH-end-groups, are crosslinked with 4,4′-diphenylmethane diisocyanate in one stoichiometric and several nonstoichiometric reactions. Dynamic mechanical (frequency 10−4 to 102 Hz) and also some dielectric (10−2 to 106 Hz) measurements were made on these networks in a wide temperature range. The time-temperature-superposition principle was used to obtain master curves. Two large relaxation processes were detected (separated by many decades of frequency in some samples). The high frequency process seems to correspond to the glass-rubber transition in linear polymers, the low frequency process is probably due to the relaxation of “dangling chains”.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01422657
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  • 10
    Electronic Resource
    Electronic Resource
    Piezoelectric resonators of InP:Fe (1994)
    Springer
    Czechoslovak journal of physics 44 (1994), S. 575-584 
    Details
    ISSN: 1572-9486
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Piezoelectric resonators in the form of rectangular platelets of semiinsulating InP∶Fe were produced by cleaving along direction {011} to excite fundamental longitudinal modes of vibrations. The analysis of the transfer function of such resonators in the region around resonance frequencies delivered such parameters as elastic modulus and piezoelectric coefficients of InP, which could be compared with values from literature. The pertinent elastic modulus agrees within 1.6%, whereas the value of piezoelectric coefficient ∥e 14∥=(1.3±20%) C/m2 is approximately three times higher than the older experimental value, but lies nearer to some theoretical predictions and to a recent experimental value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01689605
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