Influence of the fine structure on the response of polymer chains to perturbation fields
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Date
2006
Journal Title
Journal ISSN
Volume Title
Publisher
AMER CHEMICAL SOC
Abstract
The relaxation behavior of poly(3-methylbenzyl methacrylate), poly(3-fluorobenzyl methacrylate), and poly(3-chlorobenzyl methacrylate) was thoroughly studied by broadband dielectric spectroscopy with the aim of investigating the influence of slight differences in chemical structure on the response of polymers to electric perturbation fields. Retardation spectra calculated from dielectric isotherms utilizing linear programming regularization parameter techniques were used to facilitate the deconvolution of strongly overlapped absorptions. Above the glass transition temperature, the spectra of the two halogenated polymers present a secondary gamma process well separated from a prominent peak resulting from the overlapping of the alpha and beta relaxations. The spectra of poly(3-methylbenzyl methacrylate) exhibit at long times a well-developed alpha absorption followed in decreasing order of time by two weak absorptions, named beta and gamma, whose intensities increase with temperature. The temperature dependence of the distance of the a peak from the beta and gamma peaks, expressed in terms of log(f(max,beta)/f(max,alpha)) and log(f(max,gamma)/f(max,alpha)), respectively, is studied. The Williams ansatz and the extended ansatz give a fairly good account of the relaxation behavior of the polymers. The stretch exponent associated with the a relaxation increases with temperature from ca. 0.2 at low temperatures to the vicinity of 0.5 at high temperatures. At low temperatures, the alpha relaxation is described by a Vogel-type equation, but at high temperature the beta and alpha processes are roughly described by the same Arrhenius equation. In the whole temperature range, the activation energy they relaxation is significantly lower than that of the beta absorption. The mechanisms involved in the development of the secondary relaxations are qualitatively discussed.
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Keywords
GLASS-TRANSITION, BETA-RELAXATION