Slow relaxations in semicrystalline poly(butylene succinate) below and aboveT_g

Abstract

The slow molecular mobility in the amorphous part of the semi-crystalline polymer poly(butylene succinate) (PBS) has been studied by the thermally stimulated depolarization current (TSDC) technique. Experiments were carried out in the temperature range, which includes the glassy state, the glass transformation region, and the rubber state. A broad and low intensity secondary relaxation was observed in the temperature region from 2140 C up to the glass transition region; the activation energy of the motional modes of this secondary relaxation was in the range between 35 and 55 kJ mol 21 . The glass transition temperature of PBS, provided by the TSDC technique, was T g 5 240 C, and the fragility index was found to be m 5 43. The aging behavior of the main and of the secondary relaxations was analyzed. A strong relaxation above T g was observed, whose molecular origin was discussed. The thermal behavior of the PBS was also characterized by differential scanning calorimetry. POLYM. ENG.FIG. 6. Different methods to distinguish a space charge relaxation from a dipolar relaxation. (a) Evolutions of the TSD current (upper curve) and of the TSP current (lower curve). (b) Effect of the electric field strength on the polarization of the relaxation peaks of the glass transition relaxation and of the relaxation above T g . (c) TSDC thermogram of PBS obtained with different electrode/sample contacts. Curves 2 and 3 were normalized to the intensity of curve 1 at the temperature of maximum intensity, T max , of the glass transition peak.

Dielectric relaxation study of poly (ether imide) by thermally stimulated depolarization currents

“…The specific heat jump associated with the glass transition was measured by DSC, Δ C p = 0.240 ± 0.005 J g −1 K −1 (at 10 K min −1 , average of seven determinations), in good agreement with other published values: 0.210 J g −1 K −1 3 and 0.22 ± 0.04 J g −1 K −1 35 ; this value is close to that obtained for several other polymers, 14,36 so it does not give the PEI glass transition any particular specificity. On the contrary, as will be seen below, the values of the glass transition temperature, T g , and dynamic fragility, m , give the PEI a strong individuality in the amorphous polymer family.…”

“…However, the relaxations observed by TSDC above T g may also be nothing more than artifacts resulting from space‐charge motions or electron injection from the electrodes; it is thus important to find methods to clarify the origin of these relaxations observed above T g in TSDC 49–52 . The appropriate methodology for this purpose was implemented in works already published, 14,53–55 so we avoid repeating here the same explanations.…”

“……) at lower temperatures in the deep vitreous state and, at temperatures closer to T g , the β‐ or Johari–Goldstein (JG) relaxation; the distinctive character of the JG‐relaxation is that its properties bear some relationship with those of the α‐relaxation, the most relevant aspect being that the dielectric strength of the JG‐relaxation, like that of α‐relaxation, is sensitive to physical aging. As in other circumstances, 11–14 we will approach this investigation through the analysis of the effect of aging both in the global TSDC thermogram and in narrow polarization window depolarization peaks. Through this search it was possible for us to identify motional modes well separated from α‐mobility and sensitive to physical aging, which obeyed the requirements of the JG‐relaxation.…”

Structure and Dynamics of Biobased Polyester Nanocomposites

“…An area that has attracted less attention from the scientific community regarding bio-based polymers and their nanocomposites is the investigation of their dynamics, although understanding their relaxation processes is crucial in order to derive the optimum processing conditions and, thus, expand the application range of such materials. − In general, the investigation of the dynamics of polymers involves the study of bond vibrations, rotational motion of the different side groups, the α-process or segmental relaxation, and the motion of the whole chain; it is, thus, clear that an extended temporal range of more than 10 orders of magnitude, from pico-seconds (ps) to seconds (s), should be covered. The relaxation processes that are observed below the polymer glass transition temperature like the local rotation and reorientation of side groups, usually exhibit an temperature dependence τ = τ 0 exp[ E / RT ] that follows the Arrhenius law.…”

New contributions from thermal and dielectric techniques to the understanding of the dynamic properties of medium to long chain poly (propylene glycols)

“…The TSDC technique is a simple method for obtaining low‐frequency information on molecular dynamics, and has been used to study the amorphous solid state in very diverse materials, including polymers. [ 1,2,3,4 ] With TSDC we will use experimental procedures specific to the technique that allow the analysis of complex thermograms, and thus determine the distributions of activation energies and pre‐exponential factors. With regard to this technique, we are interested in evaluating the quantity and accuracy of the information that the TSDC thermogram can provide in comparison to other techniques, namely the related dielectric technique of dielectric relaxation spectroscopy (DRS).…”