DSC-curves

Fig. 1. Schematic dsc curve. Exothermic behavior iacludes cuting, oxidation, chemical reactions, cross-linking, etc.

Fig. 1. Differential scanning calorimeter (dsc) curves of three grades of low melting syndiotactic 1,2-polybutadiene. A, 90% 1,2 = 71° C B, 92% 1,2 ...

Figure 3 Two examples of heterogeneity of comonomer distribution and a possible explanation of the shape of the DSC curve. Source Ref. 32.

Figure 1 DSC curves of P7MB representing a cooling cycle (lower) starting from the isotropic melt, and the subsequent heating cycle (upper). Scanning rate 10°C/min.

The phase behavior of several polybibenzoates with oxyalkylene spacers has been reported [11,14,15,20-27]. These spacers include the dimer of trimethylene glycol and different ethylene oxide oligomers. The most noticeable characteristic of these polybibenzoates with ether groups in the spacer is the considerable decrease of the rate of the mesophase-crystal transformation. Thus, Fig. 8 shows the DSC curves corresponding to a sample of poly[oxybis(trimethylene)p,p -bibenzoate], PDTMB, with a structure similar to that of P7MB but with the... 

Fig. 4. DSC curves of precursors for Ti02 and 25-Ni0-Ti02/W0s having different WO3 contents.

Other hand, when an equimolar mixture of 2,5-DSP and l OEt is recrystallized from benzene, yellow crystals, comprising 2,5-DSP and l OEt in a molar ratio of 1 2, deposit. In the DSC curve of this crystal, a single endothermic peak is observed at 166°C, which is different from the melting point of either 2,5-DSP (223°C) or l OEt (156°C). Furthermore, the X-ray powder diffraction pattern of the crystal is quite different from those of the homocrystals 2,5-DSP and l OEt. Upon irradiation the cocrystal 2,5-DSP-l OEt affords a crystalline polymer (77i h = 1.0 dl g in trifluoroacetic acid). The nmr spectrum of the polymer coincides perfectly with that of a 1 2 mixture of poly-2,5-DSP and poly-1 OEt. In the dimer, only 2,5-DSP-dimer and l OEt-dimer are detected by hplc analysis, but the corresponding cross-dimer consisting of 2,5-DSP and l OEt is not detected at all (Hasegawa et al., 1993). These observations by nmr and hplc indicate that the photoproduct obtained from the cocrystal 2,5-DSP-l OEt is not a copolymer but a mixture of poly-2,5-DSP and poly-l OEt in the ratio 1 2. 

If no exothermic peak appears up to 500 K in DTA/DSC curves for heating rates of 5-10 K min and no other signs of vigorous reaction are observed, then the material can usually be considered safe. In case of the occurrence of a temperature peak, measurements should be repeated at lower heating rate. 

The maximum operating temperature may be evaluated from DTA/DSC curves if the shift of the peak due to reduction of the heating rate to 0.5-1 K min does not exceed 40 K. This corresponds to moderate activation energies of the secondary reactions, i.e. less than 50 kJ/mol for values obtained from the Arrhenius plots . 

Figure 9 Differential scanning calorimetric (DSC) curve showing the phase transitions observed on heating the amorphous form (glass) of polyethylene terephthalate. (Reproduced with permission from Ref. 38.)...

Figure 15. Differential Scanning Calorimetry (DSC) curve of 90% trans-i, 4-poly butadiene...

Figure 16. DSC curve of high trms-SBR (15% styrene, 85% transj prepared with Ba-Mg-Al.

In the case of 19a, it was found that the typical melting point for linear polyethylene, 134°C, with a heat diffusion of 204 Jg-1, is depressed to -2°C with a heat diffusion of 32 Jg 1. A typical DSC curve is shown in Fig. 6. 

The DSC curve of pseudoephedrine hydrochloride obtained with a Perkin Elmer DSC-1B differential scanning calorimeter is shown in Figure 5.7 The heating rate was 5°C/min. The heat of fusion is 6.4 Kcal/mol. The melting point (uncorrected) is 184°C. 

Figure 2.6C shows the temperature difference between reference and sample as recorded by differential thermal analysis (DTA). Note also the similar differential scanning calorimeter (DSC) curve later in Figure 2.13. 

FIGURE 2.7. Depletion of Inhibitor Stability DSC Curve (A) and Isothermal Curves (B) for an Inhibited Material. 

An example of an idealized DSC curve with an exotherm peak is represented in Figure 2.13. The shape of the DSC curve depends on the reaction order, the occurrence of autocatalytic decomposition, and on parameters such... 

FIGURE 2.13. Example Scanning DSC Curve of an Exothermic Decomposition. 

In DSC instruments, heat production (q) can be determined directly as a function of temperature. The shape of the heat production curve is also important for hazard identification. A sharp rise in energy release rate (i.e., a steep slope of the exotherm), whether due to a rapid increase of the rate constant with temperature or to a large enthalpy of reaction, indicates that the substance or reaction mixture may be hazardous. Figure 2.14 illustrates an example of a DSC curve with a gradual exothermic reaction, while Figure 2.15 is an example of a steep exothermic rise. 

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