Amorphous thermograms

Fig. 5. Differential scanning calorimetry thermogram. Amorphous PPS is heated from room temperature to 325°C at 20°C/min.

Polyetherimides show no crystallinity as evidenced from calorimetry measurements. The heteroarylene like phenylquinoxaline [27], oxadiazole [30], and benzoxa-zole [56] activated polyethers show TgS from DSC thermograms, with no evidence of crystallization, indicating amorphous or glassy morphology. Furthermore, wide angle x-ray scattering measurements show no evidence of crystalline or liquid crystalline type morphologies, consistent with an amorphous structure. F polyether... 

Still einother use to which DTA has been employed is the characterization of amorphous materials. The following shows a typical DTA thermogram obtained when a powdered sample of glass is run as shown in the following diagram ... 

The glass transition of solutes that remain amorphous during and after the freezing process can often be seen in the DSC thermogram as a shift in the baseline toward higher heat capacity. This is illustrated in the DSC thermogram of sucrose solution in Fig. 6, in which the glass transition is observed at — 34°C. 

An X-ray diffraction study of PHA-10UND= showed that this PHA was amorphous however, the DSC thermogram of the polymer showed a small but clear endotherm at approximately 38 °C. The glass transition temperature of PHA-10UND= is approximately - 46 °C which is significantly lower than those of the poly(nHAMCL)s. Both the melting temperature and the glass transition tempe-... 

Fig. 4.22. Complementary thermogravimetric and DSC thermograms, showing loss of a volatile component and solid-solid conversion of some of the sample from the amorphous to the crystalline phase.

Thermal Properties. A typical dsc thermogram of an HPL/PVA blend (Fig. 4) shows a single Tg and Tm (10). Differences in the shape of the melting endotherms of PVA(96), (88), and (75) can be attributed to different degrees of crystallinity in the three polymers. Changes in crystalline structure of polymer blends usually result from polymer-polymer interactions in the amorphous phase. Such interactions result in a reduction of crystallinity, thereby reducing the enthalphy of the phase change (16,17). The observed reductions in melt endotherm area of HPL blends with PVA (> 0) may therefore indicate the existence of polymer-polymer interactions between the two types of macromolecules. 

Tan 6 curves from dmta thermograms of blends based on combinations of HPL/PVA(> 0) are shown in Figure 5 (10). The tan 6 transition, which is another measure of Ts, is broadened by the presence of HPL component, and it increases above that of the parent polymers consistent with dsc data. This can again be explained with the presence of strong interactions between the amorphous components which coexist in a closely associated state. 

Differential thermal analysis (DTA) thermograms of ( )-etodolac sodium salt exhibited endothermic transitions around 80,120, and 297°C and an exothermic transition around 83°C [12]. The exothermic phase change was observed after exposure of the sample to moisture, indicating conversion of the amorphous form of ( )-etodolac sodium salt to a crystalline phase. In contrast, the thermogram of (+)-etodolac sodium salt, after exposure to moisture, showed endotherms at 60, 80, 120, and 297°C, indicating that the salt contained methanol, acetonitrile, and water. There was no sign of degradation product formation. 

FIGURE 7 Characterization of amorphous form, (a) DSC thermogram of amorphous substance. Thermogram is characterized by a glass transition temperature (Tg) above which the amorphous form is mobile and recrystallizes (Tcrys) into a crystalline form which finally melts (7m). (b) Amorphous form that does not show any peaks in XRD as it does not have regular arrangement of molecules. Shallow peaks are indicative of an amorphous drug substance. 

Figure 3.3. Comparison of DSC thermograms (top) with the corresponding variation in microhardness H (solid symbols) as a function of temperature for fully amorphous (a) PET and (b) PMMA. The vertical dashed lines denote Tg values derived from both techniques. (From Ania etfl/., 1989.)...

Recycling experiments can also be conducted whereby a sample is heated and then cooled. The thermogram may show a crystallization exotherm for the sample, which on subsequent reheating may show a melting point different from the first run. In a similar way, amorphous forms can be produced by cooling the molten sample to form a glass. 

The Fourier transform-infrared (FT-IR) spectra of two polymorphs, an amorphous form and a methanol solvate of a hydrochloride salt, are shown in Figure 3.24 (see Figure 3.17 for the corresponding DSC thermograms). The spectra can be used to give information on how the molecule is packed in the solid state and which groups of the molecule are in a different environment. As can be seen, the spectrum of the amorphous form of the compound is less well defined and reflects the multitude of molecular environments present in this form of the compound. 

Differential Thermal Analysis. Details revealed in the differential thermograms of the 4 MA-Y zeolites (Figure 2) are consistent with the TGA results. They all exhibited an endotherm (122°-190°C) caused by loss of adsorbed water. Over the region where slow decomposition occurred, there were weak endotherms or inflections in the curve, and the rapid decomposition was confirmed by a sharp endotherm (516°-577°C). Dehydroxylation was clearly revealed by the endotherm at 785°C in MMA-Y, but was not as well resolved in the others. The exotherm (977°-1026°C) was owing to mullite transformation (I). However, all the samples were found to be amorphous (by x-ray) after 1 hour at 900°C. 

Finally, a phase inversion occurs and the spherical EO domains of ca. 400 A are dispersed in the amorphous Is matrix (Figure 2e). The spherical EO domains are crystallized by wide angle x-ray diffraction (cf. diblock copolymers in Figure 4) and DSC thermograms of thin film specimens. The size of the dispersed EO domains was ca. 400 A in diameter for EO-Is-EO 5, ca. 750 A for EO-Is-EO 6, and ca. 400 A for EO-Is-EO 7. These values did not necessarily agree with the theoretical values for amorphous AB and ABA type block copolymers (3, 4, 5, 6), probably also because the EO segment is crystallizable. 

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