Analysis of the thermo-mechanical behaviour of the polymers has been and still is the subject of many rheological studies both experimentally and theoretically. For small deformations, the modelling framework retained by rheologists is often of linear viscoelasticity, which led us to the definition of complex modules and used to identify the glass transition temperature as the so called rule of time-temperature superposition principle. In this context, the effect of time is almost unanimously associated with viscous effects. It has however been observed that the dissipative effects associated with viscous effects remains often small compared with thermomechanical coupling effects, indicating a high sensitivity of polymeric materials to temperature variations. Because of heat diffusion, it was also noticed that thermomechanical couplings induce a time dependence of the material behavior. Using traditional experimental methods of visco-analysis (DMTA) and via an experimental energy analysis of the behaviour, the goal of this research work is to restate the time-temperature equivalence rule under the Thermodynamics of Irreversible Processes, taking into account not only dissipation effects but also thermomechanical coupling effects induced by the deformation process.