Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). I. Effect of Cross‐Linking Process on the Viscoelastic Properties

Madbouly, Samy A.; Ougizawa, Toshiaki

doi:10.1081/mb-120029782

Cited by 11 publications

(7 citation statements)

References 35 publications

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“…[31] At 1908C all curves of tan d at different constant shear frequencies coincided and were no longer frequency dependent, indicating that T gel ¼ 1908C. For this reason, we consider in this section the time evolution of the viscoelastic properties of the gelation process around this temperature.…”

Section: Effect Of Temperaturementioning

confidence: 93%

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Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). II. Rheological Behavior at the Gel Point

Madbouly

Ougizawa

2004

Journal of Macromolecular Science, Part B

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Isothermal time evolution measurements at different constant temperatures (1708C, 1808C, and 1908C) over a wide range of frequency for the thermal cross-linking process of poly(vinyl methyl ether), PVME, have been investigated rheologically. At the onset of cross-linking (t onset ) the elastic storage modulus, G 0 , increases abruptly. The magnitude of the elevation in G 0 and the value of t onset were found to be temperature-dependent. Similar behavior was observed for both the viscous loss modulus, G 00 and the complex dynamic viscosity, h Ã ; however, the value of G 00 shows a very low sensitivity to the cross-linking process compared to G 0 and h Ã at the same experimental conditions. The gel point, t gel , was evaluated from the point of intersection in plots of tan d vs. curing time for different constant shear frequencies. At the gel point tan d is no longer frequency-dependent, and all curves cross-over, indicating the validity of the Winter -Chambon criterion. The value of t gel obtained from the coincidence of G 0 and G 00 was about 10 min longer than that determined from tan d vs. t, indicating that the crossover of G 0 and G 00 is not be considered as a general method for evaluation of t gel . The value of the apparent activation energy of gelation determined from the temperature dependence of t gel was 74 kJ mol 21 in good agreement with literature values for other different systems. At the gel point G 0 and G 00 showed a power law with shear frequency, i.e., G 0 G 00 v n with critical exponents equal to 0.64 and 0.75, respectively, in close agreement with the percolation theory (n ¼ 2/3). The 655 ORDER REPRINTS zero shear viscosity, h 0 , and the equilibrium shear modulus, G eq , can also be expressed in power low scaling functions with the relative distance from the gel point, 1 i.e., h 0 1 2k and G eq 1 z with k ¼ 1.3 and z ¼ 2.4 in good agreement with the predicted values based on the percolation theory.

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Section: Effect Of Temperaturementioning

confidence: 93%

“…In Part I, [31] We found that poly(vinyl methyl ether), PVME, thermally cross-linked in the absence of cross-linking agent during rheological measurements at high temperatures. The linear viscoelastic properties of PVME were found to be greatly changed by the onset of the cross-linking process.…”

Section: Reprintsmentioning

confidence: 99%

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). II. Rheological Behavior at the Gel Point

Madbouly

Ougizawa

2004

Journal of Macromolecular Science, Part B

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“…A dependência do módulo G'' com a variação da temperatura em diferentes A temperatura na qual ocorre o intercruzamento dos módulos G' e G'', ou seja, o ponto no qual ambos os módulos apresentam dependência simultânea da temperatura, normalmente é utilizado para determinar o tgel (instante de gelificação), que é a temperatura à qual a estrutura reticulada tridimensional de termorrígido é formada, como mostrado na figura 31 [63,64] . Tgel, o processo de ROMP evolui e G' aumenta mais rapidamente do que G'' (isto é, G' é superior a G ''), indicando a formação de uma estrutura polimérica reticulada tridimensional [64] .…”

Section: Varredura Da Temperaturaunclassified

“…Tgel, o processo de ROMP evolui e G' aumenta mais rapidamente do que G'' (isto é, G' é superior a G ''), indicando a formação de uma estrutura polimérica reticulada tridimensional [64] .…”

Section: Varredura Da Temperaturaunclassified

“…As figuras 33 demonstra a dependência dos módulos O Tgel pode ser determinada de forma mais precisa a partir da variação de tan com o aumento da temperatura em diferentes frequências angulares constantes [64] . Mais precisamente no ponto em que tan  é independente da frequência e todas Um rápido aumento no modulo G' foi observado nos estágios iniciais (t <10 min) devido ao processo de ROMP nas temperaturas de medição mais baixas.…”

Section: Varredura Da Temperaturaunclassified

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Water effect on the rheologic behavior of PAN solution during thermal‐induced gelation process

Tan

Pan

2011

Polymers for Advanced Techs

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The thermal‐induced gelation process in a polyacrylonitrile (PAN) solution containing different amounts of water was investigated through both dynamic and steady‐state rheologic measurements. During the cooling process, the storage modulus G′ was found to intersect with the loss modulus G″ at a temperature which can be considered as the incipient gel point Tig. This crossover point increased with the water content in the PAN solution. On the basis of the power law $G'\tilde{G}\tilde{\omega} {}^{n} $ and the relation ${\rm tan}\ \delta = G(\omega )/G^{'}(\omega ) = {\rm tan}(n\pi /2) = {\rm const}$, the loss tangent tan δ was traced with decreased temperature at various oscillation frequencies, and a crossover point was observed at the temperature a little higher than the Tig above for all PAN solutions. The water content might affect the value of the relaxation exponent n via two different mechanisms, that is, hydration decoupling of the pendant nitrile groups in PAN at low water content (2 wt% water) and molecule aggregation at high water content (4 and 6 wt%). Nevertheless, the slight difference in the n values reflects the unique structure of the critical gels irrespective of the water level. The apparent viscosity ηa of either the PAN solution or the PAN gel was found to rise with increased water content and both showed pronounced shear‐thinning behavior. Compared with temperature, the water effect on the apparent viscosity ηa is more significant due to the water‐induced aggregation of the molecular chains. Copyright © 2010 John Wiley & Sons, Ltd.

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Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). I. Effect of Cross‐Linking Process on the Viscoelastic Properties

Cited by 11 publications

References 35 publications

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). II. Rheological Behavior at the Gel Point

Thermal Cross‐Linking of Poly(Vinyl Methyl Ether). II. Rheological Behavior at the Gel Point

Desenvolvimento de novas combinações monômero - catalisador para a produção de polímeros via ROMP

Water effect on the rheologic behavior of PAN solution during thermal‐induced gelation process

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