Browsing by Author "Pagueguy, C"

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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 relaxations of poly(2-norbornyl methacrylate) and poly(3-methyl-2-norbornyl methacrylate)
    (ELSEVIER SCI LTD, 2001) Diaz Calleja, R; Garcia Bernabe, A; Pagueguy, C; Gargallo, L; Radic, D
    Dielectric behaviour of poly(2-norbornyl methacrylate) (P2NBM) and poly(3-methyl-2-norbornyl methacrylate) (P3M2NBM) was studied. The effect of the methyl substituent on the norbornyl ring is to decrease the temperature of the dynamic glass transition about 50 K. Moreover, weak secondary relaxations are observed in the two polymers under study. The secondary process of P3M2NBM has been conveniently analysed in terms of the empirical Fuoss-Kirkwood (F-K) equation. (C) 2001 Elsevier Science Ltd. All rights reserved.