Influence of static strain on dynamic mechanical behavior of amorphous networks prepared from aromatic polyesters

Dynamic mechanical experiments were performed between ?140 and 50°C on both poly(diethylene glycol isophthalate) and poly(triethylene glycol terephthalate) networks. Plots of loss tangent versus temperature show a well-defined α peak, associated with the transition from glasslike to rubberlike consistency, and two overlapping peaks (β₁ and β₂) in the glassy region. Dynamic deformations of small amplitude were superimposed on large static deformations. It was found that the position of the β₁ and β₂ peaks as well as their intensities are independent of the static elongation ratio. However, the intensity of the loss tangent associated with the glass–rubber transition tends to decrease with increasing static deformation. Moreover, the position of the maximum of the α peaks shifts to lower temperatures as the elongation ratio increases. This behavior suggests that for both networks the volume effects (shifting the α peaks to lower temperatures with increasing elongation ratio) overcome the entropic effects (shifting the α peaks to higher temperatures with decreasing entropy).