Semicrystalline polymers peak with

PTEB-Q) to the annealed ones, owing to the presence of the crystalline phase. Moreover, the temperature of the peak increases with the annealing, as well as the broadness of the relaxation. These results suggest that the liquid crystalline phase gives raise to an a relaxation similar to that of amorphous polymers despite the existence of the two-dimensional order characteristic of smectic mesophases, and it changes following the same trend than that of semicrystalline polymers. 

PTT is a semicrystalline polymer with a DSC peak melting point of 228 °C (Figure 11.5). The equilibrium melting points, 7m°, obtained from the... 

The relaxation behavior of selected semicrystalline ESI is depicted in Figure 26.3. It can be seen that the loss peak evident in the temperature range —50 to +50 °C shows increasing breadth of the relaxation process as the styrene content in ESI decreases. The relaxation processes associated with this loss peak are complex in nature. The relaxation behavior of semicrystalline polymers is fundamentally different from that of amorphous polymers. The long-range segmental motions associated with the Tg process become hindered owing to the restrictions imposed by the crystallites. 

Poly(vinyl fluoride) is a semicrystalline polymer with a planar, zigzag conformation.The degree of crystallinity can vary significantly from 20-60% and is a function of defect structures. Commercial PVF is atactic, contains approximately 12%o head-to-head linkages, and displays a peak melting point of about 190°C (52,53,62,63). Poly(vinyl flouride) displays several transitions below the melting temperature. Lower Tg occurs at — 15 to —20°C and upper Tg is in the 40-50°C range. Two other transitions at 80 and 150°C have been reported. 

The diffraction peaks obtained with a perfect crystal are in theory expected to be infinitely sharp. The finite widths of the observed diffraction peaks as seen in Figure 3.2 reflect the fact that crystallites in semicrystalline polymers are not perfect, and the analysis of the line widths can tell us about the nature and degree of imperfection in the polymer crystal lattices and the size of the polymer crystallites if they are small. 

In polymer characterization, it is possible to determine the degree of crystallinity of semicrystalline polymers. The noncrystalline (amorphous) portion simply scatters the X-ray beam to give a continuous background, whereas the crystalline portion gives diffraction lines. A typical schematic diffraction spectrum of a semicrystalline polymer is shown in Fig. 8.46. The ratio of the area of diffraction peaks to scattered radiation is proportional to the ratio of crystalline to noncrystalline material in the polymer. The ultimate quantitative analysis must be confirmed using standard polymers with known percent crystallinity and basing the calculation on the known ratio of crystalline diffraction to amorphous scattering. 

Fig. 3.31). The length axis L of the tape is vertical, so the (110), (040) and (13 0) diffraction peaks lie on the equator of the figure. When semicrystalline polymers are stretched, the crystal c axes tend to align with the tensile direction, here the L axis. The assumed crystal orientation distribution is of c axes perfectly aligned with the L axis, with a and b axes randomly distributed in the plane perpendicular to L. Therefore, the hkO) poles, at 90° to the c axis, should be perpendicular to the tape L axis. The diffraction peaks in Fig. 3.31 are consistent with this assumption. If in Fig. 3.29 the L axis is normal to the paper, the diffracting planes in the crystal shown are of the hkQ) type. As the [hkO) poles in the PP tape are randomly oriented in the plane of the diagram, many crystals will be positioned to produce diffraction spots on either side of the equator of the pattern. To confirm the orientation distribution, further diffraction patterns should be taken as the sample is rotated around its L axis. 

Obtain DSC thermal curves of several semicrystalline polymers such as polymethylmethacrylate (PMMA), polystyrene, polycarbonate, high-density (HD) polyethylene, and low-density (LD) polyethylene, and look for the glass transition in these polymers. The DSC run may need to be repeated twice with rapid cooling between runs. Many as received polymers will show a small peak on top of the glass transition on the first run due to relaxation effects in the polymer. The second run should not show this peak, but only a step change in the baseline. Compare your values of to literature values. Deviations may indicate the presence of plasticizers or other additives in the polymer. 

Fig. 6. This schematic diagram shows waxs patterns corresponding to the crystallization of a semicrystalline polymer. One can see the problems that one can encounter in the data analysis of time-resolved data. The first frame shows the amorphous ring characteristic of a molten polymer. In the second frame the previous frame is shown as a dotted line. The amorphous ring has slightly diminished in intensity and two small peaks have started to grow. In the following frames the diffraction peaks gain in intensity while the amorphous halo keeps diminishing. Between frames 4 and 5 the diffraction peaks move to lower q-values. If one now wants to follow the intensity of the diffraction peaks one has to subtract an ever changing background and also one has to take into account the peak movements. Mathematically this is a trivial problem but to do this in an automated way with software is nontrivial.

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