New secondary relaxation in polymeric glasses: A possible common feature of the glassy state

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Abstract
New sub-glass-transition-temperature relaxation processes, other than secondary β relaxation, have been detected by means of both thermally stimulated depolarization current (TSDC) and thermally stimulated creep (TSC) techniques in several structurally different polymeric glasses. These processes have characteristics similar to those of the so-called α’ relaxation recently found in various metallic glasses. They occur at a temperature located just below the glass-transition temperature and are widely distributed but have a nearly constant activation energy. The Arrhenius-like apparent kinetic parameters, deduced from the relaxation-time temperature behavior, are interpreted in terms of compensation laws. This analysis implies that these new relaxation processes could be interpreted as precursors of the glass transition associated with local conformational changes and thereby they should be present in all kinds of glasses. This interpretation, compatible with different theoretical approaches to the relaxation behavior in the glass-transition range, enables us to consider the glass⇆liquid transition as a localization⇆delocalization transition in the structural mobility.