Browsing by Author "Sanchis, MJ"

Now showing 1 - 7 of 7
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    Comparative study of localized side group in poly(2,3 and 4 methyl cyclohexyl methacrylate)s. TSDC measurements
    (ELSEVIER SCI LTD, 2005) Dominguez Espinosa, G; Sanchis, MJ; Diaz Calleja, R; Pagueguy, C; Gargallo, L; Radic, D
    By means of thermal sampling techniques, the fine structure of the gamma-relaxation zone of poly(methyl cyclohexyl methacrylate)s (P2MCHMA), (P3MCHMA), (P4MCHMA) were analyzed. Results reveal that in this relaxation zone, at least two peaks are present. These peaks are attributed to the cis and trans isomers. Loss permittivity of the polymers under study in this relaxation zone has been reproduced from the partial depolarization data by using the elementary relaxation times and activation energies. Results are in relatively good agreement with the experimental data previously obtained. Molecular mechanic calculations have been carried out in order to elucidate the characteristics and molecular origin of the relaxations observed in this zone. An interpretation of the height of the peaks associated to the cis- and trans-isomer in terms of strain energy (SE) have been carried out. (c) 2005 Elsevier Ltd. All rights reserved.
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    Comparative study of poly(2,3 and 4 methyl cyclohexyl methacrylate)s. Dielectric relaxation spectroscopy (DRS)
    (ELSEVIER SCI LTD, 2005) Dominguez Espinosa, G; Sanchis, MJ; Diaz Calleja, R; Pagueguy, C; Gargallo, L; Radic, D
    The relaxation properties of poly(methyl cyclohexyl methacrylate)s (P2MCHMA), (P3MCHMA), (P4MCHMA) were analyzed. Dielectric spectroscopy (DS) techniques were used for this purpose. These polymers exhibit prominent alpha peaks, associated to the dynamic glass transitions, and then poorly defined beta-relaxations and two other relaxation zones labelled as gamma and delta-relaxation in order of decreasing temperatures. The alpha relaxation processes were analyzed by means of the free volume theory, using the Vogel-Fulcher-Tammann-Hesse (VFTH) equation and in terms of the Havriliak-Negami (HN) empirical equation. Previously to these analyses, conductive contributions to the loss permittivity were subtracted. The apparent activation energies for the secondary processes under study have been calculated by means of Arrhenius. Comparison with previous relaxation results of poly(cyclohexyl methacrylate) (PCHMA), i.e. the polymer without substituents in the cyclohexyl ring, has been also carried out. In this way, changes in the glass transition absorptions as well as in the secondary processes have been discussed. (c) 2005 Elsevier Ltd. All rights reserved.
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    Dielectric relaxational behavior of poly(diitaconate)s containing cyclic rings in the side chain
    (WILEY, 2003) Diaz Calleja, R; Garcia Bernabe, A; Sanchez Martinez, E; Sanchis, MJ; Hormazabal, EA; Gargallo, L; Radic, D
    Dielectric relaxations of several poly(diitaconate)s with cyclobutyl, cycloheptyl, and cyclooctyl groups in the side chain were investigated. The study was performed by determining the dielectric permittivity and loss, depending on the frequency and temperature. Dynamic dielectric measurements indicated several relaxations according to the chemical structure of the polymers. The dielectric behavior of these polymers was compared with those of poly(dicyclohexyl itaconate), previously reported. The a relaxations were analyzed with the Havriliak-Negami equation. Significant differences in the subglass relaxations were observed. A tentative explanation of the molecular origin of each absorption was proposed in terms of the number of carbon atoms of the ring and their conformational versatility. Strong conductive processes were observed in these polymers at low frequencies and high temperatures. (C) 2003 Wiley Periodicals, Inc.
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    Dynamic mechanical and dielectric relaxations in poly(di-n-chloroalkylitaconates)
    (ELSEVIER SCI LTD, 2004) Sanchis, MJ; Diaz Calleja, R; Pelissou, O; Gargallo, L; Radic, D
    Dielectric and viscoelastic relaxation measurements have been carried out on poly(2-chloroethyl diitaconate) (PDCEI) and poly(3-chloropropyl diitaconate) (PDCPI) between 123 K and temperatures about 293 K above the glass transition temperatures.
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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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    Dynamic mechanical and dielectric relaxations of poly(difluorobenzyl methacrylates)
    (WILEY-BLACKWELL, 2000) Diaz Calleja, R; Sanchis, MJ; Saiz, E; Martinez Pina, F; Miranda, R; Gargallo, L; Radic, D; Riande, E
    This work reports the mechanical and dielectric relaxation spectra of three difluorinated phenyl isomers of poly(benzyl methacrylate), specifically, poly(2,4-difluorobenzyl methacrylate), poly(2,5-difluorobenzyl methacrylate) and poly(2,6-difluorobenzyl methacrylate). The strength of the dielectric glass-rubber relaxation of the 2,6 difluorinated phenyl isomer is, respectively, nearly three and two times larger than the strengths of the 2,5 and 2,4 isomers. The 2,4 isomer presents a mechanical ct peak the intensity of which is nearly two times that of the other two isomers. Both the mechanical and dielectric relaxation spectra display a subglass process, called gamma relaxation, centered in the vicinity of -50 degrees C at 1 Hz and, in some cases, a subglass beta absorption is detected at higher temperature partially masked by the glass-rubber relaxation. The mean-square dipole moments per repeating unit, [mu 2]/x, measured at 25 degrees C in benzene solutions, are 2.5 D-2, 1.9 D-2, and 5.0 D-2 for poly(2,4-difluorobenzyl methacrylate), poly(2,5-difluorobenzyl methacrylate) and poly(2,6-difluorobenzyl methacrylate), respectively. These results, in conjunction with Onsager type equations, permit to conclude that auto and cross-correlation contributions to the dipolar correlation coefficient may have the same time-dependence. On the other hand, dipole intermolecular interactions, rather than differences in the flexibility of the chains, seem to be responsible for the relatively high calorimetric glass-transition temperature of the 2,6 diphenyl isomer, which is, respectively, nearly 36 degrees C and 32 degrees C above the T-g's of the 2,4 and 2,5 isomers. Molecular Mechanics calculations give a good account of the differences observed in the polarity of the polymers. (C) 2000 John Wiley & Sons, Inc.
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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.