Enthalpy relaxation studies in polymethyl methacrylate networks with different crosslinking degrees

Alves, Natália M.; Ribelles, J.L. Gómez; Mano, João F.

doi:10.1016/j.polymer.2004.11.016

Cited by 68 publications

(74 citation statements)

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“…The phenomenological shift has been widely accepted in applying SC model. 8,[10][11][12][13][14] The behaviour of the configurational entropy was schematically represented in Figure 1 for the liquid state (equilibrium), for an experimental scan at finite rate (solid line), and for the hypothetical limit of the structural relaxation process. The simplest shape is assumed for S c lim (see Figure 1), which leads to a constant shift parameter for the heat capacity.…”

Section: Discussionmentioning

confidence: 99%

“…Afterwards, another model was proposed in reproducing DSC curve on the basis of the configurational entropy; here this is called as SC model. [8][9][10][11][12][13] The basic feature which is common to both models is the application of Boltzmann superposition principle, which enables to calculate the quantities of the state corresponding to the thermal history the polymer had experienced.These two models currently accompany several variations to predict DSC results accurately. 7,[14][15][16] The arguments are taken on the equation to define .…”

mentioning

confidence: 99%

“…9 However, the introducing in SC model can be seen in almost all the modelling studies reported concerning the enthalpy relaxation of polymer. 8,10,11,[13][14][15]34 The proposed measure for the structural relaxation of PCBA6 is the value of as mentioned in the introduction section. determined through the configurational entropy, that is written as ðSÞ , is defined as follows,…”

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confidence: 99%

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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: Discussionmentioning

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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 broadness of the transition is typical 26,27 of crosslinked polymers made by free radical polymerization and corresponds to the heterogeneous distribution of crosslinks in the network. The knots hinder the mobility and the domains with different degree of crosslinking show different T g 0 s, too close to be resolved in separated transitions.…”

Section: Sem Micrographs Shown Inmentioning

confidence: 99%

Discrimination of the roles of crosslinking density and morphology in the swelling behavior of crosslinked polymers: Poly(N‐vinylimidazole) hydrogels

Pacios

Piérola

2009

J of Applied Polymer Sci

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The degree of swelling (S) of crosslinked polymers depends on several variables whose individual contributions are difficult to be distinguished. The aim of this work is to determine the contributions of the morphology to S, discriminating them from the effect of the crosslinking density. Under usual conditions of synthesis, these two characteristics vary simultaneously but here, several samples of chemically crosslinked poly(N-vinylimidazole) having the same permanent crosslinking density (determined by DSC) and different porous morphologies (determined by SEM) were prepared. It was thus found that the variation of S with porosity, keeping constant the rest of variables, is strongly solvent dependent. Swelling in methanol is almost constant whereas for ethanol, deionized water, and aqueous HCl solutions, S depends on morphological features in a different way for each medium. It was concluded that S increases with inherent porosity and solvent effects arise from the counterbalance of such increment with the dependence of the polymer-solvent interaction parameter on the polymer volume fraction.

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“…Additionally, the constraints imposed by the crosslinks also results in a decrease in ΔC p (T g ), related to the presence of orderly packing of polymer molecules, which lowers the mobility at T g (Alves, et al, 2005;Scott, et al, 2002).…”

Section: Mdsc Measurementsmentioning

confidence: 99%

A contribution to the study of the molecular mobility in polymeric materials by Thermal and Dielectric Analysis

Foj¹,

Belén²

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T h e s i s S u p e r v i s o r : P R O F . D r . M a r í a J e s ú s S a n c h i s S á n c h e z t o o b t a i n t h e d e g r e e o f D o c t o r o f P h i l o s o p h y a t t h e U n i v e r s i t a t P o l i t è c n i c a d e V a l è n c i a Prof. Dr. María Jesús Sanchis SánchezThe work presented in this thesis was carried out at the Universitat Politècnica de València and was financially supported by the Spanish Ministry of Economy and Competitiveness (Projects Nos. MAT2008-06725-C03-03 and MAT2012-33483)."Cuando quieres algo, todo el Universo conspira para que ACKNOWLEDGEMENTSTras estos años de trabajo, llega el momento de mostrar mi agradecimiento a todas las personas que me han acompañado y apoyado durante el desarrollo de mi tesis doctoral.En primer lugar, me gustaría expresar mi gratitud a mi directora de tesis María J.Sanchis por su inestimable ayuda durante todos estos años. Muchas gracias por confiar en mí, por darme esta oportunidad y por las incalculables horas invertidas tanto para el desarrollo de esta tesis como al mío propio.También me gustaría agradecer a mis estimadas compañeras Marta Carsí y Pilar Ortiz su ayuda y amistad en este largo recorrido que suponer realizar una tesis doctoral. He aprendido mucho de vosotras tanto científica como personalmente. En este punto, no puedo olvidarme de mi querida Aurora Alonso, que pese a no formar parte de nuestro grupo de investigación, me ha apoyado, aconsejado y dado su amistad durante todos estos años.Quiero mostrar mi agradecimiento a los profesores José M. García y Félix C. García ABSTRACTThe development of new and more complex polymeric materials involves challenging problems to basic sciences. The relationship between structure and molecular dynamics assumes great importance for the future development of novel technologies based on such polymers. Thus, the understanding of how small changes in the chemical structure affect the properties of the material is essential to progress in the technological and scientific area. An in-depth analysis of the molecular mobility leads to establish the structure-properties relationships. On this basis, the main aim of the present work is to study the molecular mobility of two different families of polymeric materials. For this purpose, the experimental techniques mainly used were Differential Scanning Calorimetry (DSC) and Dielectric Relaxation Spectroscopy (DRS) (Chapter 3).The first family of polymers characterized was a series of chemically cross-linked copolymers composed by Vinylpyrrolidone (VP) and Butyl Acrylate (BA) monomers. The study was divided in two parts, which are collected in Chapter 4 and 5.In the first place, Chapter 4 contains the influence of the monomer molar ratio (XVP/YBA) on the copolymer properties. Thus, a Fourier Transform Infrared Spectroscopy (FTIR) analysis verified dipole-dipole interactions between amide groups. The influence of these interactions on several parameters related to the molecular mobility was evidenced by the DSC, DRS and Dynamic Mechanical Analysis (DMA) techni...

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Enthalpy relaxation studies in polymethyl methacrylate networks with different crosslinking degrees

Cited by 68 publications

References 74 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

Discrimination of the roles of crosslinking density and morphology in the swelling behavior of crosslinked polymers: Poly(N‐vinylimidazole) hydrogels

A contribution to the study of the molecular mobility in polymeric materials by Thermal and Dielectric Analysis

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