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

Abstract

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 above T g exhibit a blurred relaxation resulting from the overlapping of secondary relaxations with the glass−rubber or α relaxation. At high temperatures and low frequencies, the α 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 (α) 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 α′ absorption. The α and α′ 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 γ′, γ, and β followed by the α relaxation. At long times and well separated from the α absorption the α′ 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 discussed.

Relaxational study of poly(vinylpyrrolidone-co-butyl acrylate) membrane by dielectric and dynamic mechanical spectroscopy

“…Moreover, the characterization of the α relaxation, directly related to the glass transition, is sometimes difficult to carry out for wet membranes. This is related to the high intensity of the water conductive effects, which masks or does not allow a clear definition of the α relaxation [25,[32][33].…”

Effect of slight crosslinking on the mechanical relaxation behavior of poly(2-ethoxyethyl methacrylate) chains

“…For example, chair-inverse-chair conformational transitions of cyclohexyl in poly(cyclohexyl methacrylate) produce an ostensible secondary  relaxation that causes a significant decrease of the real relaxation modulus of the polymer in the glassy state [10][11][12]. Since to date, while no quantitative theory that describe the glass-rubber relaxation and the secondary relaxations in terms of the chemical structure has been formulated, (i) the theory of the total dielectric relaxation strength for the -process is wellestablished in terms of molecular dipole moments [4][5][6][13][14][15][16][17][18][19][20][21][22] and (ii) much success has been achieved in understanding the characteristic behavior of the dielectric  relaxation through computer "molecular dynamics" simulations [23][24][25][26][27][28][29]. In this sense, actually the design of polymers with specific physical properties relies on empirical rules based on experimental studies of the relaxation properties of polymers with different chemical structures.…”

Conductivity and Time–Temperature Correspondence in Polar Viscoelastic Liquids

“…However, after the plateau, ε′ further increases with decreasing frequency until a second plateau is reached at a frequency that roughly coincides with the frequency ω c , which marks the onset of the ac conductivity in the σ′ isotherms. The interpretation of the X-ray diffractograms of PDMB23 carried out elsewhere 18 suggests the presence of nanodomains in the viscoelastic liquid, formed by polar side groups which are flanked by the backbone. Long distance charge transport across the interfaces of the nanodomains produces a distributed MWS relaxation, reflected in the increase of ε′ from the first to the second plateau.…”

“…Poly(2,3-dimethoxybenzyl methacrylate) (PDMB23) was taken as the model, whose repeat unit is shown in Figure 1. Earlier work carried out on this polymer 18 showed that side groups segregation from the backbone promotes relatively long distance charge jumps, reflected as a distributed Maxwell−Wagner−Sillars (MWS) relaxation 19−23 in the low frequency side of the spectra. The aim of this work is to inquire the effects of the MWS process and the strong dispersive processes, arising from the complex motions of polar viscoelastic liquids, on the time−temperature correspondence of the ac conductivity.…”