Dielectric relaxation in amorphous linear aliphatic copolyesters

In order to contribute to a more extensive body of experimental knowledge concerning the relaxation processes in glass-forming amorphous polymers, broad-band frequency dielectric measurements have been carried out on two examples of a model amorphous polar polymer system. The system consists of a linear random copolyester with one-to-one mole ratios of adipic acid and succinic acid coupled with glycol units. In one example, ethylene glycol is the coupling unit and in the other it is trimethylene glycol The subglass beta relaxations as well as the primary a regions were characterized and emphasis was placed on phenomenological description of the coalescence of the two regions with increasing temperature. Each subglass process was found to be complex in the sense of exhibiting two partially resolved components. One component is a typical extremely broad-in-frequency subglass relaxation and the other component is weaker, narrower in frequency and occurs at lower frequency isothermally or higher temperature isochronally. Tentative assignments of the source of the beta process components are made. Phenomenological analysis of the alpha-beta coalescence region invoking the Havriliak-Negami and Cole-Cole functions and utilizing numerical regression indicates that the merging process is optimally described as the beta process losing relaxation strength and its presence being expressed as increased skewing in the primary relaxation. (C) 2008 Elsevier Ltd. All rights reserved.