A phenomenological study of the structural relaxation of poly(methyl methacrylate)

Ribelles, J.L. Gómez; Ribes‐Greus, A.; Calleja, R. Dı́az

doi:10.1016/0032-3861(90)90110-k

Cited by 72 publications

(29 citation statements)

References 14 publications

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“…These results shows that the peak position is influenced by both the ageing temperature and time. In addition, c p ðTÞ peaks appeared at temperatures above T g in all the measured DSC curves, as happens in other polymers of poly(methylmethacrylate), 28 poly(vinyl chloride) 30 polystyrene 31 and poly(-benzyl-L-glutamate).…”

Section: Resultssupporting

confidence: 63%

Enthalpy Relaxation of Liquid Crystalline Polymer with Cyanobiphenyl Group in the Side Chain: Analysis based on Configurational Entropy Model with the AG Expression

Tanaka

2009

Polym. J.

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The enthalpy relaxation of poly(cyanobipheny hexylacrylate) has been studied by differential scanning calorimetry. The experimental results of the heat capacity (c p ) were compared with the prediction of a phenomenological model for the process of structural relaxation based on the configurational entropy (S c ) and the relaxation time expressed by the Adam-Gibbs equation. This model follows the evolution of the configurational entropy of the sample during the whole thermal history including an isothermal annealing. The parameters of the model were calculated by simultaneous fits to the experimental results. With the calculation result, the peak position appeared in DSC curve of c p was interpreted using the plot of temperature dependence of S c . The plot showed that S c rapidly approached to the configurational entropy of equilibrium (S c eq ) in the narrow temperature range around T g , which is often referred to as the recovery of enthalpy, and thus the recovery of S c , in interpreting the enthalpy relaxation. As the measure of structural relaxation upon the isothermal ageing, the value of relaxation function () was considered, which estimates the departure from the equilibrium. The correlation between of S c and of enthalpy is also presented. The physical properties of the liquid crystalline polymer with cyanobiphenyl groups in the side chain (PCBA) have been studied with respect to the effects of molecular weight and spacer length.1,2 In the previous paper, the enthalpy relaxation measured using Differential Scanning Calorimetry (DSC) was analysed with the activation energy spectrum (AES) model. 3This model provides information about thermally activated processes which are available to contribute to observed changes in the properties upon physical ageing. For the enthalpy relaxation of PCBA6 (PCBA in which the spacer length is 6), the analysis gives the relation between the process number and the activation energy, in other words, the distribution of the relaxation process.In general, the decrease in enthalpy upon the isothermal ageing at temperature below the glass transition temperature T g , is closely related to the structural relaxation toward equilibrium in the glassy state. Concerning the relaxation of PCBA6, the optical texture was shown to vary in the previous paper, as an evidence of structural change. The change in optical texture is being considered as the coarsening dynamics of the disclinations. That is to say, the dynamics of PCBA6 molecules bring about the change in structure.On the other hand, the modelling approaches for enthalpy relaxation of polymer have been reported, which attempts to reproduce the measured DSC curve using quantities of state. The quantities of state employed are the configurational entropy, S c , and the fictive temperature, T f . 4,5 It has been shown that the main features of the relaxation process can be modelled on the basis of a distribution of relaxation times that depends both on the temperature and on the structure of the material represented by the value o...

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Section: Resultssupporting

confidence: 63%

Enthalpy Relaxation of Liquid Crystalline Polymer with Cyanobiphenyl Group in the Side Chain: Analysis based on Configurational Entropy Model with the AG Expression

Tanaka

2009

Polym. J.

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“…Anyway, these results suggest that the experimental procedure used in evaluating DH ðT a ; t a Þ only provides an approximation by defect of the enthalpy change during the annealing step; this approximation becomes very good only for very low annealing temperatures [43]. Fig.…”

Section: Resultsmentioning

confidence: 97%

“…They found some appreciable differences between the different stereospecific forms of PMMA, but in all the cases a great thermal history dependence of the model parameters were observed, especially at long annealing times. G o omez Ribelles et al [43] also found discrepancies between the parameters describing different experimental thermograms. Furthermore, the predicted values for the enthalpy lost at two aging temperatures highly overestimated the experimental data.…”

Section: Theoretical Frameworkmentioning

confidence: 93%

Enthalpy recovery in low molecular weight PMMA

Andreozzi

Faetti

Giordano

et al. 2003

Journal of Non-Crystalline Solids

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“…Equation 8a is the William-Watts equation (Williams and Watts, 1970) and has been used describe relaxation effects, including physical aging (Tribone et al, 1986;Agrawal, 1989;Gomez Ribelles et al, 1990;Hay, 1993;Montserrat, 1994). Three parameters, ⌬H max , t c and ␤, were determined using a nonlinear least squares fit to Eq.…”

Section: Physical Agingmentioning

confidence: 99%

Physical Aging of Maltose Glasses

Schmidt¹,

Lammert²

1996

Journal of Food Science

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Physical aging is the alteration in the physical properties of a glass, as a function of time, at temperatures below its glass transition temperature (Tg). The physical aging of maltose glasses, prepared from maltose monohydrate sugar, was studied using differential scanning calorimetry (DSC). The maltose was aged at 30ЊC for times ranging from 5 min to Ϸ10 days. The Tg and change in heat capacity of the unaged and aged maltose glasses were measured. The change in enthalpy relaxation with aging time was determined by integrating the difference between the aged and the unaged DSC thermograms. The enthalpic relaxation data were adequately described by the Williams-Watts equation.

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A phenomenological study of the structural relaxation of poly(methyl methacrylate)

Cited by 72 publications

References 14 publications

Enthalpy Relaxation of Liquid Crystalline Polymer with Cyanobiphenyl Group in the Side Chain: Analysis based on Configurational Entropy Model with the AG Expression

Enthalpy Relaxation of Liquid Crystalline Polymer with Cyanobiphenyl Group in the Side Chain: Analysis based on Configurational Entropy Model with the AG Expression

Enthalpy recovery in low molecular weight PMMA

Physical Aging of Maltose Glasses

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