Dielectric properties above the glass transition for a series of epoxide prepolymers

Koike, Tsuneo; Tanaka, Ryôhei

doi:10.1002/app.1991.070420516

Cited by 42 publications

(53 citation statements)

References 23 publications

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“…The concentrations of Na ϩ and Cl Ϫ are very low and similar among these oligomers as described in a previous study. 26 The size of the ion is much smaller than that of the oligomer molecule. The critical volume for the ion transport is considered similar among the oligomers having different M w 's from 1396 to 2640.…”

Section: Critical Volume For the Transport Of Moving Unitmentioning

confidence: 99%

“…The behavior of ␥* for the ion mobility is also explained in the following way: The four epoxide oligomers were produced from the same raw materials by the same production process, which is a conventional one. 26,30 These oligomers are considered to have the same kinds of ions. The major ions in the epoxide oligomers are Na ϩ and Cl Ϫ due to the manufacturing process.…”

Section: Critical Volume For the Transport Of Moving Unitmentioning

confidence: 99%

“…The measurement of the gel permeation chromatography was described elsewhere. 26 The ratio of M w and the number-average molecular weight (M n ), M w /M n , is an indication of the molecular weight distribution. In Table I, the M w / M n value is listed for each oligomer along with the content of the n ϭ 0 component in the structural formula of the oligomer previously shown.…”

Section: Experimental Materialsmentioning

confidence: 99%

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Free volume and dipole mobility in an epoxide oligomer before crosslinking

Koike

Ishizaki

1999

J. Appl. Polym. Sci.

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ABSTRACT:The free volume of a bisphenol-A-type epoxide oligomer (DGEBA) was studied using Williams-Landel-Ferry parameters and thermal expansion coefficients above and below the glass transition temperature (T g ). The values of the free-volume fraction at the T g are around 0.02 for the DGEBA oligomers having weight-average molecular weights (M w 's) from 1396 to 2640. The dipole mobility, which was obtained from the analysis of the temperature dependence of the dielectric relaxation time, was compared with the segment mobility in terms of the critical volume for the transport of each moving unit. The critical volume for the segment transport increases with increase of the M w of the oligomer. The critical volume for the dipole movement, on the other hand, is not different between the oligomers studied (1396 Յ M w Յ 2640), which leads to that the dipole mobility in the epoxide oligomer is smaller than is the segment mobility. The low mobility of the dipole is considered to result from the molecular interaction restricting the dipole movement, especially in a smaller M w oligomer.

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Section: Critical Volume For the Transport Of Moving Unitmentioning

confidence: 99%

Section: Critical Volume For the Transport Of Moving Unitmentioning

confidence: 99%

Section: Experimental Materialsmentioning

confidence: 99%

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Free volume and dipole mobility in an epoxide oligomer before crosslinking

Koike

Ishizaki

1999

J. Appl. Polym. Sci.

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“…However, very few data were reported about the effects of high temperatures on the dielectric properties of thermoset resins. 27,28 In this effort, thermoset resins (BMI, EP, and VE resins) were exposed to temperatures well above the glass transition for a short period of time. The changes in the dielectric properties of the resins were studied to evaluate their sensitivity to thermal exposure and to predict the mechanical performance of heat-exposed resins.…”

Section: Introductionmentioning

confidence: 99%

Thermal degradation analysis of thermoset resins

Chatterjee

2009

J of Applied Polymer Sci

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Dynamic mechanical analysis, thermogravimetric analysis, and dielectric analysis (DEA) were conducted for three thermoset resin systems: bismaleimide, epoxy, and vinyl ester. The resin samples were subjected to various degrees of thermal exposure (400, 270, and 330 C for 5-150 min). Dielectric constants were measured along with the thermomechanical properties. The glasstransition temperature, modulus, and weight loss were important parameters for correlating the material property changes with the heat exposure. A linear relation was determined between the thermomechanical properties and the dielectric properties of the resins under the selected exposure conditions. Therefore, DEA can be introduced as a significant technique for evaluating thermally exposed polymer materials. Interestingly, it is a nondestructive evaluation process. In the future, it could be used for onsite health monitoring of thermally exposed polymer matrix composite structures.

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“…These methods need, for the description of the ␣-relaxation peak, a broad distribution of relaxation times and often yield unphysical values for the pre-exponential factors [5] that are usually less than 10 Ϫ 30 sec. Recently, the dielectric response of this peak has been related to the melt viscosity for some epoxide oligomers [6,7]. Furthermore, TSDC ␣-peaks for poly(vinylacetate), PVA, were detected for different cooling and heating conditions to study the influence of physical ageing on the electrical properties of this particular relaxation, that is, how it depends on the thermal history of the sample [8].…”

Section: Introductionmentioning

confidence: 99%

Phenomenological Model to Describe the Glass Transition Relaxation Peaks for Depolarization Current Experiments

Puma¹

1997

Polym. Adv. Technol.

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A simple phenomenological pseudo‐equilibrium dipolar model is presented to characterize the dipolar relaxation related to the glass transition temperature of some polymers as measured by thermally stimulated depolarization current (TSDC) experiments. To characterize the normalized TSDC relaxation current peak only three parameters are necessary. The first is the measured glass transition temperature of the relaxation. The second is related to the proposed phenomenological energy term and is linked to the behavior of the specific heat observed by differential scanning calorimetry experiments. The last is the zero order approximation near the glass transition temperature, Tg, of the Williams–Landel–Ferry expression describing the temperature dependence of the relaxation time. A first order approximation for the relaxation time gives a somewhat better description of the low‐temperature side of the relaxation peak. To take into account the nonequilibrium character of this transition, the parameters in the model are functions of the cooling and heating rates used during the experiment. In general, they are functions of the thermal and electrical history of the sample. Some actual experimental data used to test this model will be presented and discussed. © 1997 John Wiley & Sons, Ltd.

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Dielectric properties above the glass transition for a series of epoxide prepolymers

Cited by 42 publications

References 23 publications

Free volume and dipole mobility in an epoxide oligomer before crosslinking

Free volume and dipole mobility in an epoxide oligomer before crosslinking

Thermal degradation analysis of thermoset resins

Phenomenological Model to Describe the Glass Transition Relaxation Peaks for Depolarization Current Experiments

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