The DSC Curve

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

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... 

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. 

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. 

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... 

In this table, Tg, Tg and T have the same meaning as in Table I. Typical DSC traces for these reactive polymers are presented in Figure 6. This figure presents the DSC curves of a,U>-bis(hydroxy-phenyl)PSU-2, a,u-bis(benzylether)PSU-2 and a,u>-bis(benzylether)PSU-2 containing 0.57 vinyl groups per bisphenol-A unit. As was previously... 

In DSC measurements, the weight percent of a phase was calculated using the peak area of the DSC curve and its reported heat of formation. For example, weight percent of the p-MgHj in a reactively milled powder can be estimated using the peak area of the DSC curves and the reported P-MgHj heat of formation (-74 kJ mol [175], which equals to -2,811 J g ). The DSC curve was analyzed by the NETZSCH thermal analysis software. First, the onset and end temperature of the peak were determined. Then, the peak area was calculated using the linear approach from the onset temperature to tlie end temperature (Fig. 1.37) by the DSC software. 

The basis for all calorimetric measurements is the determination of heat capacities. In the absence of any other transition, the DSC curve represents the change in the heat capacity of the sample over the experimental temperature range [5,24]. Detailed descriptions of experimental procedures and data treatment for using DSC to measure heat capacities are available [1,2,5,25-29] A simplistic approach is given below. 

Considering only the assumption of no difference in the heating rates for the sample and the reference and that the DSC curve then returns to the original baseline after the transition, then the enthalpy can be described in the following way ... 

Generally, the crystalline melting point of a polymer corresponds to a change in state from a solid to a liquid and gives rise to an endothermic peak in the DSC curve [3,9], The equilibrium melting point may be defined as... 

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