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  • 1
    Electronic Resource
    Electronic Resource
    Relaxations in thermosets. XXVI. Ultrasonic studies of the temperature dependence of curing kinetics of diglycidyl ether of bisphenol-A with catalyst (1994)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 32 (1994), S. 1465-1474 
    Details
    ISSN: 0887-6266
    Keywords: ultrasonics ; curing kinetics ; diglycidyl ether of bisphenol-A ; thermosets ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Longitudinal velocity and attenuation of the unreacted diglycidyl ether of bisphenol-A and dimethylbenzylamine mixture have been measured for 1 MHz ultrasonic frequency. These are combined with our earlier data [Alig et al., Acta Polymerica, Vol. 40, p. 590 (1989)], which were measured during the curing process of the thermoset, and then analyzed in terms of a process involving a negative feedback between molecular diffusion and chemical reaction. The complex plane plots of the real and imaginary components of the longitudinal modulus are fitted to a stretched exponential relation, and the structural relaxation time is calculated at different stages of curing at temperatures in the range 333-403 K. The results are compared against the calorimetric, dielectric, and viscosity measurements and it is shown that, at least for two cases, gelation time can be observed from the longitudinal modulus data. © 1994 John Wiley & Sons, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1994.090320818
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  • 2
    Electronic Resource
    Electronic Resource
    Curing kinetics of phase separating epoxy thermosets studied by dielectric and calorimetric investigations: A simple model for the complex dielectric permittivity (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2461-2470 
    Details
    ISSN: 0887-6266
    Keywords: dielectric relaxation spectroscopy ; thermosets ; interpenetrating polymer networks ; curing reaction ; temperature-modulated differential scanning calorimetry ; glass transition ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Dielectric relaxation spectroscopy (3 kHz ≤ ƒ ≤ 3 MHz), differential scanning calorimetry, and temperature-modulated calorimetry have been performed during isothermal curing of an epoxy network (diglycidylether of bisphenol A crosslinked with diaminodiphenyl methane), and of two thermoplast modified epoxy resins (semi-interpenetrating polymer networks) consisting of the epoxy network component and different amounts (10 and 20 wt %) of a linear high Tg polymer (polysulfone or polyethersulfone). During reaction, the homogeneous-mixtures phase separate into an epoxy-rich and a linear polymer-rich phase with different mobilities of the electrical dipoles. The complex dielectric permittivity is composed of a contribution from the ionic dc-conductivity and a contribution from relaxations of the permanent electrical dipoles in the two phases. The decrease of the dc-conductivity in the initial stage of cure is related to the time for gelation or vitrification. The contribution of the dipole relaxations to the dielectric permittivity reflects an increase of the relaxation times with curing time for both phases. The time-dependent changes in the complex dielectric permittivity are described by a simple two-phase model based on two Havriliak-Negami functions combined with Vogel-Fulcher equations for the description of the curing-time dependence of the relaxation times. The increase of the relaxation times in the phases during isothermal curing is incorporated by time-dependent Vogel temperatures. The latter are related to the time evolution of the glass-transition temperatures in the two phases measured independently by calorimetry. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2461-2470, 1998
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Relaxations in thermosets. XVIII. Ultrasonic studies of curing kinetics of ethylene-diamine-cured epoxide (1992)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 30 (1992), S. 791-799 
    Details
    ISSN: 0887-6266
    Keywords: relaxations in thermosets in curing, ultrasonic study of ; epoxide, ethylenediamine cured, relaxations in ; kinetics of epoxide curing, ultrasonic study of ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Velocity and attenuation of longitudinal acoustic waves in a frequency range of 5-16 MHz have been measured during the curing of diglycidyl ether of bisphenol-A with ethylene diamine. The velocity monotonically increases and reaches a limiting value and the attenuation reaches a maximum and thereafter decreases as curing proceeds. Both kinds of data have been transformed into a complex-longitudinal-modulus formalism. The complex-plane plots of the longitudinal modulus show an arc-skewed shape at the long (curing) time end. It is fitted, for the initial phase of curing, to a stretched exponential decay function with an exponent γ = 0.22 to 0.28. These results then are considered in terms of a process with a negative feedback between molecular diffusion and chemical reactions to obtain the increase in the relaxation time with the curing time. This increase is sigmoidal. Calculations of the complex longitudinal modulus show the consistency of our formalism.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1992.090300801
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  • 4
    Electronic Resource
    Electronic Resource
    Relaxations in thermosets. XIX. Dielectric effects during curing of diglycidyl ether of bisphenol-A with a catalyst and the properties of the thermoset (1993)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 31 (1993), S. 299-311 
    Details
    ISSN: 0887-6266
    Keywords: dielectric relaxation ; curing kinetics ; thermoset ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Changes in the dielectric permittivity ε′ and loss epsiv;″ during the curing of DGEBA catalyzed by 10 mole % dimethylbenzylamine have been studied from sol to gel to glass formation regions at different temperatures from 323 to 390 K. The ε′ monotonically decreases with time of cure, and ε″ initially decreases by several orders of magnitude and then increases to reach a peak value before finally decreasing to a low value characteristic of the glassy state. The features shift to shorter times and the peak vanishes as the curing temperature is increased. The decrease of ε″ at the initial stage of cure has been analyzed in terms of dc conductivity σ0, which follows a power law, σ0 ∝ (tg-t)x, as well as a new singularity equation, σ0 ∝ exp[-B/(t0-t)] where tg, x, B, and t0 are empirical constants that vary with the curing temperature; tg is close to the time for gelation; and t0 ≥ time for vitrification. The dielectric properties of the thermoset formed after different periods of cure have been studied from 77 to 325 K. Similar studies of the thermosets formed at different temperatures have been made. Increase in the curing period decreases the heights of both the γ-and α-relaxation peaks and increases their separation, while a β-relaxation peak emerges. Isothermal curing at high temperatures decreases the height of the γ peak to a vanishingly small value and increases that of the β peak from a vanishingly small value. In both the uncured and fully cured states, there is only one sub-Tg relaxation process named γ for the uncured and β for the cured state. These results are discussed in terms of our general physical concepts of local mode motions in an amorphous matrix. © 1993 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/polb.1993.090310308
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  • 5
    Electronic Resource
    Electronic Resource
    Film foration and crystallization kinetics of polychloroprene studied by an ultrasonic shear wave reflection method (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 2949-2959 
    Details
    ISSN: 0887-6266
    Keywords: ultrasound ; crystallization kinetics ; film formation ; polychloroprene ; shear modulus ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: We report the application of an ultrasonic shear wave reflection technique for the investigation of film formation and crystallization kinetics of one amorphous and two semicrystalline polychloroprene samples with different gel content. Both isothermal and temperature-dependent measurements of the complex dynamic shear modulus (G* = G′ + iG″) have been performed at a frequency of 5.32 MHz. The process of film formation during the evaporation of water is expressed by a stepwise increase of the shear modulus. For the semicrystalline samples a further increase, which is due to crystallization, can be observed. Film formation and crystallization are delayed for the sample with high gel content and its minor final modulus is explained by a lower degree of crystallinity. The time-dependent increase of the shear modulus due to the growth of spherulites has been analyzed by the Avrami equation combined with the Kerner model for the modulus of a two-phase composite (spherulites in an amorphous matrix). The dynamic shear modulus for the spherulites has been estimated by a model introduced by Halpin and Kardos. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2949-2959, 1998
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Comparison of ultrasonic shear wave and dynamic-mechanical measurements in acrylic-type copolymers (1998)
    Bognor Regis [u.a.] : Wiley-Blackwell
    Journal of Polymer Science Part B: Polymer Physics 36 (1998), S. 1703-1711 
    Details
    ISSN: 0887-6266
    Keywords: complex shear modulus ; ultrasonic measurements ; dynamic-mechanical measurements ; acrylic-type copolymers ; film formation ; glass-rubber relaxation ; Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: An ultrasonic shear wave reflection method was applied to study film formation and temperature dependence of the complex shear modulus (G*=G′ + iG″) in different amorphous films made of aqueous dispersions of acrylic-type copolymers. The data are compared with dynamic-mechanical measurements in the low frequency range. It is shown that the temperature dependence of the storage (G′) and the loss modulus (G″) for both methods can be fitted by the same set of parameters using the Havriliak-Negami function incorporating the Vogel-Fulcher-Tamman-Hesse equation for the temperature dependence of relaxation times. The temperature dependence of the relaxation times obtained from the fits to the ultrasonic shear modulus is compared to the shift factors of the dynamic-mechanical measurements. The agreement between both methods is good. This suggests an almost thermorheological simplicity of the samples for the main glass-rubber relaxation and demonstrates the capacity of the ultrasonic rheometer. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1703-1711, 1998
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Two-component diacrylate networks from liquid-crystalline and non-liquid-crystalline monomers I. Synthesis of the monomers, phase behaviour of the binary monomer mixtures, network formation (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 250 (1997), S. 105-117 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Aus Bisacrylaten wurden durch photoinduzierte Vernetzung in der isotropen Phase zweikomponentige Netzwerke synthetisiert. Bei allen Systemen wurde als eine Komponente ein Bisacrylat verwendet, das eine flüssigkristalline Phase bilden kann, und als zweite Komponente ein Bisacrylat, das dazu nicht in der Lage ist. Die isotrope Komponente wurde hinsichtlich ihrer Größe, Geometrie und Polarität variiert. Für alle Systeme wurden mittels einer Wärmeflußkalorimetrie (DSC) Phasendiagramme der Monomermischungen erstellt. Das Phasenverhalten der Systeme zeigt eine Abhängigkeit vom Schmelzpunkt und der chemischen Struktur der isotropen Zweitkomponente. Die Vernetzungstemperatur wurde so gewählt, dafß die Vernetzung in der isotropen Phase 10 °C über der Phasenllbergangstemperatur erfolgte. Die Reaktionskinetik wurde aus den Photopolymerisationsenthalpien mittels eines für photochemische Vernetzungen modifizierten DSC-Gerätes untersucht. Die Zeitabhängigkeit des Umsatzes und der Gesamtumsatz an Acrylatbindungen wurden aus den DSC-Kurven ermittelt. Der Gesamtumsatz hängt nicht von der Reaktionstemperatur und der Struktur der Monomeren ab und liegt je nach Zusammensetzung füralle Systeme zwischen 53 und 71%. Die Zeitabhängigkeit des Umsatzes hingegen wird von der Struktur des nicht flüssigkristallinen Comonomeren beeinflufßt.
    Notes: Two-component networks of diacrylate monomers were synthesized by photoinduced polymerization in the isotropic phase. In all systems one component was a liquid-crystalline diacrylate, whereas the second component was a non-liquid-crystalline diacrylate, which was varied in size, geometry and polarity. The phase behaviour of the monomer mixtures has been analysed by differential scanning calorimetry (DSC). It is influenced by the melting point and the structure of the non-liquid-crystalline component. All samples were cross-linked in the isotropic phase 10°C above the phase transition temperature and a modified differential scanning calorimeter was used to investigate the enthalpies of photopolymerization. The final value and the time dependence of the conversion of acrylate double bonds were calculated from the DSC curves. The final degree of conversion of the acrylate double bonds was between 53 and 71% for all samples, whereas no significant dependence of the degree of conversion on the chemical structure of the monomers or the reaction temperature has been found. In contrast, the time dependence of the conversion was influenced by the chemical structure of the non-liquid-crystalline component.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052500108
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  • 8
    Electronic Resource
    Electronic Resource
    Two-component diacrylate networks from liquidcrystalline and non-liquid-crystalline monomers II. small- and wide-angle x-ray scatteringFor Part I see11 (1997)
    Weinheim : Wiley-Blackwell
    Angewandte Makromolekulare Chemie 250 (1997), S. 119-131 
    Details
    ISSN: 0003-3146
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: Die Struktur von Duromeren aus zwei in der isotropen Phase photochemisch vernetzten Bisacrylaten wurde anhand von Klein- und Weitwinkelröntgenuntersuchungen charakterisiert. Bei allen Systemen konnte eine Komponente eine flüssigkristalline Phase bilden, während die andere Komponente keine flüssigkristalline Phase besaß und in ihrer chemischen Struktur (Größe, Geometrie und Polarität) variiert wurde. Die Streuprofile der einkomponentigen Netzwerke im Kleinwinkelbereich zeigen Inhomogenitaten der Elektronendichte von einigen zehn Nanometem. Fur die zweikomponentigen Duromeren wird kein zusatzlicher Streubeitrag gefunden, der durch Zusammensetzungsinhomogenitaten verursacht wird. Dies ist ein Hinweis dafur, daB wahrend der photochemisch induzierten Vernetzungsreaktion keine Phasenseparation auftritt. Dieses Bild einer einphasigen amorphen Struktur wird durch Streuexperimente im Weitwinkelbereich bestatigt. Die Streuprofile der einkomponentigen Duromeren zeigen ein breites Maximum, dessen korrespondierende charakteristische Lange mit der GroBe und Geometrie der Monomeren korreliert ist. Auch fur die zweikomponentigen Netzwerke wird nur eine charakteristische Lange gefunden, die entsprechend der Zusammensetzung zwischen denen der einkomponentigen Duromeren liegt. Die Strukturuntersuchungen ergeben auch keinen Hinweis auf die Bildung einer flussigkristallinen Phase wahrend der Vernetzung.
    Notes: The structure of single- and two-component networks of diacrylate monomers which were synthesized by photoinduced polymerization in the isotropic phase has been investigated by small- and wide-angle X-ray scattering. In all systems one component was a liquid-crystalline diacrylate whereas the second component was non-liquid-crystalline. The chemical structure (size, geometry, and polarity) of the second component was varied. For the single-component networks the scattering profiles in the small-angle regime reveal inhomogeneities of the electron density of the order of some ten nanometers. For the two-component networks no additional scattering contribution due to composition inhomogeneities has been found. This is an evidence that no phase separation occurs during the photoinduced cross-linking of the thermosets. This picture of an amorphous single-phase structure is supported by the scattering profiles in the wide-angle regime. For the single-component networks a broad maximum is found, the corresponding characteristic length of which can be correlated with the structure of the monomers. For the two-component networks also only one characteristic length is found which shifts with composition between the length of the single-component thermosets. By both methods no indication for the development of a liquid-crystalline phase during network formation has been revealed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/apmc.1997.052500109
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  • 9
    Electronic Resource
    Electronic Resource
    Ultraschalluntersuchungen an Vinylchlorid-Vinylidenchlorid-Copolymer-Lösungen (1986)
    Weinheim : Wiley-Blackwell
    Acta Polymerica 37 (1986), S. 342-347 
    Details
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The results of investigations of ultrasonic absorption of poly(vinyl chloride) and poly(vinyl chloride-co-vinylidene chloride) solutions are presented. The ultrasonic spectra reflect the influence of the variation of the microstructure on the molecular motion. In the high frequency range of the spectra discrete relaxation processes were observed which can be explained by local rotational isomeric processes in the main chain. In the low frequency range a distribution of relaxation times occurs which can be explained by an increasing chain flexibility due to the VDC content or by loss mechanisms due to intramolecular interactions of the vinylidene chloride component.
    Notes: Die Ergebnisse von Ultraschallabsorptionsuntersuchungen an Polyvinylchlorid- und Vinylchlorid- Vinylidenchlorid- Copolymer-Lösungen werden mitgeteilt. In den Ultraschallspektren spiegelt sich der Einfluß der Variation der Mikrostruktur auf das Bewegungsverhalten wider. Im Hochfrequenzteil des Spektrums wurden diskrete Relaxationen nachgewiesen, die durch relativ lokale Rotationsisomerieprozesse der Hauptkette erklärt werden können. Im Niederfrequenzbereich zeigen die Copolymere ein breites Relaxationsspektrum, das durch die erhöhte Kettenflexibilität infolge der VDC-Anteile erklärt werden kann bzw. seine Ursache in Verlustmechanismen auf Grund zwischenmolekularer Strukturen durch die Vinylidenchlorid-Cokomponente hat.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/actp.1986.010370604
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  • 10
    Electronic Resource
    Electronic Resource
    Ultraschalluntersuchungen an Poly(propylenoxid) - Molekülmassenabhängigkeit und Lösungsmitteleinfluß (1986)
    Weinheim : Wiley-Blackwell
    Acta Polymerica 37 (1986), S. 698-703 
    Details
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: The acoustic absorption coefficient of poly(propylene oxide) samples of different molecular mass (Mn = 500 to 3500) has been studied in the frequency range from 0.1 to 100 MHz at 20°C and 35°C. Furthermore, the dynamic shear viscosity of some of the samples has been measured in the frequency range from 0.02 to 90 MHz. For samples of molecular masses above M ≈ 1300, a change has been observed in the frequency dependence of the effective as well as the shear viscosity which can be explained by intermolecular effects. To characterize this process a sample of poly(propylene glycol) (Mn = 2660) was investigated, where the hydroxyl groups were converted. The high frequency range of the spectra can be described by the formula α/f2∼f-n with n ≈ 0.2 bis 0.3. It was attempted to describe the high frequency spectra within the subchain concept. For a sample with Mn = 520 an additional relaxation process was observed connected to increasing influence of OH endgroups with decreasing molecular mass. In order to characterize the motional processes the influence of a solvent was studied.
    Notes: An Poly(propylenoxid)proben verschiedener Molekülmassen (Mn = 500 bis 3500) wurden Ultraschallabsorptionsuntersuchungen in einem Frequenzbereich von 0,1 bis 100 MHz bei 20°C und 35°C durchgeführt. Darüber hinaus wurde an einigen Proben die dyanmische Scherviskosität im Frequenzbereich von 0,02 bis 90 MHz gemessen. Für Proben mit Molekülmassen über M ≈ 1300 wurde eine Veränderung des Charakters der Frequenzabhängigkeit sowohl für die effektive Viskosität als auch für die dynamische Scherviskosität beobachtet, die mit zwischenmolekularen Effekten erklärt werden kann. Zur Charakterisierung dieses Verhaltens wurden Untersuchungen an einer Poly(propylenglykol)probe (Mn = 2660) durchgeführt, bei der die OH-Endgruppen umgesetzt wurden. Der Hochfrequenzteil des Spektrums kann nach der Beziehung α/f2∼f-n mit n ≈ 0,2 bis 0,3 beschrieben werden. Es wird versucht, das Hochfrequenzspektrum im Rahmen des Subkettenkonzeptes zu interpretieren. Für eine Probe mit Mn = 520 wurde ein zusätzlicher Relaxationsprozeß festgestellt, der mit dem zunehmenden Einfluß der OH-Endgruppen bei Verringerung der Molekülmassen erklärt wird. Zur Charakterisierung der Bewegungsprozesse wurde der Lösungsmitteleinfluß untersucht.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/actp.1986.010371108
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