Amorphous relaxation peaks

Dynamic mechanical measurements were made on PTEE samples saturated with various halocarbons (88). The peaks in loss modulus associated with the amorphous relaxation near —90°C and the crystalline relaxation near room temperature were not affected by these additives. An additional loss peak appeared near —30° C, and the modulus was reduced at all higher temperatures. The amorphous relaxation that appears as a peak in the loss compliance at 134°C is shifted to 45—70°C in the swollen samples. 

Similarly to the behavior of isotropic poly(ether ester)s the amplitude and position of the relaxation peaks in the loss curve of the extnidates were influenced by the composition of the amorphous phase. This is determined by the concentration and the degree of polymerization of the ester segments. For the extnidates the observed effect was pronounced only in the case of material C. Here, the glass transition temperature, as determined from the maximum of the so-called a-relaxation peak, increased linearly with decreeing extrusion temperature from - 4 C to 17 For the materials A and B the glass transition temperatures were found to be — 59 and - 50 °C, respectively, independently of the extrusion conditions. 

Other. As a result, the difference between the crystalline and amorphous phases appears in the relaxation times and chemical shifts. Fyfe et al. [1] and Earl and VanderHart [2] independently observed the chemical shift difference between the crystalline and amorphous phases for polyethylene. Figure 7.1 shows a spectrum of polyethylene measured by the CPMAS method. If all of the methylene units in polyethylene are identical, the NMR spectrum gives only one peak. However, a strong peak and shoulder are observed in the real spectrum, which means that there exists two inequivalent methylene units in the solid polyethylene. From measurements on polyethylenes with various crystalline/amorphous ratios, peaks at about 33 and 31 ppm are attributed to the crystalline and amorphous phases, respectively [3]. Figure... 

Fig. 6.12 Illustration of (a) the storage modulus, the loss modulus and the loss factor as a function of frequency across the glass transition temperature of amorphous polymers (b) the loss factor as a function of temperature according to the time-temperature superposition principle. Below the a peak for glass transition, there are secondary relaxation peaks...

Dynamic mechanical measurements (DMA) provide information that is complementary to the creep and stress relaxation experiments. Frosini and Butta studied amorphous wholly aromatic polyamides and found for PpPTA small relaxation peaks at about 15 °C, 145 °C and above 330 °C [195]. Except for the peak at 15 °C, the peak heights are much smaller than those measured for aUphatic and partially aromatic polyamides. The peak at 15 °C is identified as a -relaxation and probably caused by the motions of free amide groups. The a-relaxation or... 

Taking into account the findings of Geil et al [15-19] based on the direct study of wholly amorphous linear PE, that the Tg of PE is -80°C on the one hand, and on the other, that branched PE is supposed to have a much higher Tg value (corresponding to the / -relaxation peak), one can consider the extrapolated Tg value of -23°C from branched PE samples as the Tg of completely amorphous branched PE [50]. 

Fig. 4. Specific heat of A, PS (low temperature relaxation peak) (28) B, amorphous epoxy resins (EP) (27) and C, 98% crystaUine high density polyethylene (HDPE) (14) vs temperature. D, a curve for a filled epoxy resin, is included. Tb convert J to cal divide by 4.184.

Comparison of Figs. 8.2 and 8.8 revealed that the only difference between bulk and spheres is the appearance of a relaxation peak in e" centered at -125 °C for 1 Hz. Although this peak has not been reported before, and it is not visible in other confining geometries, we may speculate that this relaxation peak is actually a local relaxation that can be better observed here than in the bulky system since in the present case, the crystallinity is lower and therefore, relaxations in the amorphous chain become more obvious. As temperature increases, the maximum of this relaxation process shifts towards higher frequencies and the relaxation peak becomes sharper. Similar with what it has been observed in the dielectric... 

Figure 2.23 The Tg of indomethacin heated at 10°C/min after cooling from the melt at 1°C/min. This sample did not crystallise on cooling so low cooling rates could be investigated whilst retaining the amorphous structure. The enthalpic relaxation peak is clearly seen on top of the Tg.

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