Dipolar and Ionic Relaxations of Polymers Containing Polar Conformationally Versatile Side Chains

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 aim 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 aboveTg exhibit a blurred relaxation resulting from the overlapping of secondary relaxations with the glass-rubber or R relaxation. At high temperatures and low frequencies, the R 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 decreasing frequency until a plateau is reached corresponding to the glass-rubber (R) relaxation. However, at high temperatures, the real permittivity starts to increase again with decreasing frequency until a second plateau is reached, a process that presumably reflects a distributed Maxwell-Wagner-Sillars relaxation or R0 absorption. The R and R0 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 the frequency domain using linear programming regularization parameter techniques. The spectra exhibit three secondary absorptions named, in increasing order of time γ0, γ, and β followed by the R relaxation. At long times and well separated from the R absorption the R0 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- (dimethoxybenzyl 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 discussedThis work was financially supported by the DGCYT and CAM through Grant MAT2008-06725-C03. D.R. andL.G. thank Fondecyt,Grants 1080007 and 1080026, for partial financial helpPeer reviewe