Browsing by Author "Riande, C."

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    Dipolar and Ionic Relaxations of Polymers Containing Polar Conformationally Versatile Side Chains
    (AMER CHEMICAL SOC, 2010) Sanchis, M. J.; Carsi, M.; Ortiz Serna, P.; Dominguez Espinosa, G.; Diaz Calleja, R.; Riande, C.; Alegria, L.; Gargallo, L.; Radic, D.
    This work reports a comparative study of the response of poly(2,3-dimethoxybenzyl methacrylate), poly(2,5-dimethoxybenzyl methacrylate). and poly(3,4-dimethoxybenzyl methacrylate) to electrical perturbation fields over wide frequency and temperature windows with the arm of investigating the influence of the location of the dimethoxy substituents in the phenyl moieties on the relaxation behavior of the polymers The dielectric loss isotherms above T-g exhibit a blurred relaxation resulting from the over lapping of secondary relaxations with the glass rubber or alpha relaxation. At high temperatures and low frequencies, the a relaxation is hidden by the ionic conductive contribution to the dielectric loss As usual, the real component of the complex dielectric permittivity in the frequency domain increases with deer easing frequency until a plateau is reached corresponding to the glass rubber (alpha) relaxation However, at high temperatures, the real permittivity starts to increase;Warn with decreasing Frequency until a second plateau is reached, a process that presumably reflects a distributed Maxwell-Wagner-Sillars relaxation or alpha' absorption The a and alpha' processes appear respectively as asymmetric and symmetric relaxations in the loss electrical modulus isotherms in the frequency domain. To facilitate the deconvolution of the overlapping absorptions, the time retardation spectra of the polymers were computed from the complex dielectric permittivity in frequency domain using linear programming regularization parameter techniques The spectra exhibit three secondary absorptions named. in increasing order of time gamma', gamma, and beta followed by the a relaxation At long times and well separated from the a absorption the alpha' relaxation appears The replacement of the hydrogen of the phenyl group in position 2 by the oxymethyl moiety enhances the dielectric activity of the poly(dimes hoxybenzyl methacrylate)s The temperature dependence of the relaxation times associated with the different relaxations is studied, and the molecular origin of the secondary relaxations is qualitatively discussed