Browsing by Author "Calleja, RD"

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    Dynamic mechanical and dielectric absorptions in poly(2-tert-butylcyclohexyl methacrylate) and poly(4-tert-butylcyclohexyl methacrylate)
    (2000) Calleja, RD; Bernabé, AG; Sanchez-Martínez, E; Hormazábal, A; Gargallo, L; Radic, D
    Dynamic mechanical and dielectric relaxations of poly(2-tert-butylcyclohexyl methacrylate) (P2tBCHM) and poly(4-tert-butylcyclohexyl methacrylate) (P4tBCHM) have been measured. The tert-butyl group inhibits the chair-to-chair motions in the cyclohexyl ring. However, small motions of the cyclohexyl group are still possible giving rise to subglass relaxations in both polymers. The dielectric response is more sensitive than the mechanical one to the corresponding applied force fields (C) 2000 Elsevier Science Ltd. All rights reserved.
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    Dynamic mechanical and dielectric relaxational behavior of poly(cyclohexylalkyl methacrylate)s
    (AMER CHEMICAL SOC, 2001) Calleja, RD; Garcia Bernabe, A; Sanchez Martinez, E; Hormazabal, A; Gargallo, L; Gonzalez Nilo, F; Radic, D
    The dynamic mechanical and dielectric behavior of three poly(cyclohexylalkyl methaerylate)s with different spacer groups has been studied. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity epsilon*. Results are discussed in terms of the effect of the side chain structure and the insertion of flexible spacer groups. Molecular dynamic calculations for the repeating unit of the polymers under study are analyzed. Close to room temperature the interconversion between axial and equatorial conformations is not observed whitin the total time of 5 ns. The analysis was then performed from 1000 to 1500 K, and the results were extrapolated to lower temperatures. By this way the fraction of axial and equatorial conformations was calculated. The free energy change against the number of carbon atoms in the side chain is in excellent agreement with the experimental data. This means that the gamma relaxation associated with the chair-to-chair conformational change in the cyclohexyl group is also influenced by the length of the spacer group. The molecular dynamics approach allows to observe the relative incidence of the two conformations of the cyclohexyl group which can be related to the motions responsible for the gamma relaxation.
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    Dynamic mechanical and dielectric relaxations in poly(dibenzyl itaconate) and poly(diethylphenyl itaconate)
    (ELSEVIER SCI LTD, 2000) Calleja, RD; Martinez Pina, F; Gargallo, L; Radic, D
    Dynamic mechanical and dielectric behaviour of poly(dibenzyl itaconate), and poly(diethylphenyl itaconate) were studied. The study was performed by determining the components of the complex relaxation modulus E* and the complex dielectric permittivity epsilon*. The results are compared with those previously reported for poly(benzyl methacrylate), poly(monobenzyl itaconate) and poly(monoethylphenyl itaconate). The results are discussed in terms of the effect of flexible spacer groups and of the different steric hindrance between mono and disubstituted polymers. (C) 1999 Elsevier Science Ltd. All rights reserved.
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    Dynamic mechanical and dielectric relaxations in poly(monoethylphenyl itaconate)
    (1997) Calleja, RD; Sanchis, MJ; Gargallo, L; Radic, D
    Dynamic mechanical and dielectric relaxational behavior of poly(monoethylphenyl itaconate) at different frequencies and temperatures was studied. Three relaxation zones are found. The dynamic mechanical response is dominated by a relaxation peak at room temperature, labeled beta relaxation. Two prominent shoulders labelled as gamma and alpha relaxations are observed. Because of the overlapping of the alpha and gamma with the beta relaxation, a deconvolution method to improve the understanding of these phenomena is proposed. In spite of the complexity of the experimental spectra, the proposed deconvolution method seems to be a convenient approach to interpret the relaxational behavior of this polymer. (C) 1997 John Wiley & Sons, Inc.
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    Dynamic mechanical and dielectric relaxations in poly(pentachlorophenyl methacrylate)
    (WILEY-V C H VERLAG GMBH, 1998) Calleja, RD; Jaime's, C; Sanchis, MJ; San Roman, J; Gargallo, L; Radic, D
    In the present work, a comparative study of the dynamic mechanical and dielectric properties of two related polymers, poly(pentachlorophenyl methacrylate) (PPCPM) and poly(phenyl methacrylate) (PPhM), was carried out. In both polymers a similar relaxational behaviour was observed. Dielectric relaxation measurements give an improved resolution as compared with that obtained from dynamic mechanical techniques for a given process. The polymers show a secondary loss peak at approximately room temperature and a prominent peak overlapped with the conductivity electrode polarization contributions at temperatures above the glass transition temperature, studied by dielectric relaxation measurements. The activation energy associated with the relaxation process at low temperature is about 77 kJ.mol(-1) (which is similar to that observed in poly(alkyl methacrylates)) whose origin is attributed to the hindered partial rotation of the carboxymethyl group. An improved method of separating dipolar contributions from the non-dipolar ones was used to characterize the high temperature relaxation process and to obtain information from the diffusion coefficient of the conducting species.
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    Mechanical and dielectric properties of bulky side chain poly(methacrylates). Analysis of the low frequency phenomena .1. Poly(5-indanyl methacrylate)
    (SOC PLASTICS ENG INC, 1997) Calleja, RD; Jaimes, C; SanchisSanchez, MJ; MartinezPina, F; Gargallo, L; Radic, D
    This paper composes the dynamic mechanical and dielectric relaxation properties for Poly (5-indanyl methacrylate) (P51M), a polymer with a bulky side chain. Measurements were carried out from about -100 degrees C to near 250 degrees C. A secondary loss peak was observed in dielectric measurements at room temperature (20 degrees C at 0.1 Hz.), whereas nothing was resolved in the mechanical spectrum, A prominent alpha relaxation associated with the glass transition was also observed near 107 degrees C at 0.1 Hz. in the dielectric and the mechanical spectra. Dipolar dielectric loss overlapped with conductivity at high temperatures and low frequencies. A new method to split the conductive, interfacial, and dipolar contributions to the spectrum is proposed.
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    Relaxational study of poly(2-chlorocyclohexyl methacrylate) by thermally stimulated current, dielectric, and dynamic mechanical spectroscopy
    (AMER CHEMICAL SOC, 1999) Sanchis, MJ; Calleja, RD; Gargallo, L; Hormazabal, A; Radic, D
    A comparative study of the mechanical and dielectric relaxation spectra of poly(2-chlorocyclohexyl methacrylate) (P2CCM) is reported. Two clear relaxational zones are found. The spectra present a moderate subglass gamma absorption, followed in increasing temperature order by a prominent a glass-rubber relaxation process. The last peak is not clearly observed in dielectric measurements due to conductivity effects which overlap the loss permittivity spectrum. Moreover, evidence of remnant mechanical as well as dielectric activity is observed near room temperature. This phenomenon has already been observed in poly(2-chlorocyclohexyl acrylate) (P2CCA). To describe in a suitable way these results, a deconvolution method has been proposed to get information about the relaxational behavior of this polymer. A more detailed analysis about the third relaxation called beta, between alpha and gamma relaxations, has been achieved by using the thermally stimulated depolarization current technique (TSDC). Special attention was devoted to the analysis of the molecular motion that produces dielectric and mechanical activity in glassy P2CCM as well as to link the elementary TSDC to the ac dielectric spectra. A comparative study of P2CCM and P2CCA is also reported.