Melt recrystallization

The base is extracted with ether, dried with potassium carbonate, the ether removed by distillation and the residue fractionated. The 4-(5 -diethylaminopentyl-2 -amino)-7-chloro-quinoline (BP 212° to 2l4°C/0.2 mm) is obtained. On cooling the compound solidifies crystalline. It melts, recrystallized from benzene, at BB°C. The base combines with phosphoric acid to yield a diphosphate salt. 

Focusing attention on PTEB, it has been found that, similar to the case of PDTMB, the mesophase experiences a very slow transformation into the crystal. Thus, only the isotropization is observed in a sample freshly cooled from the melt [27]. However, after a long time at room temperature, the transformation mesophase-crystal is produced, owing to a glass transition temperature of about 14°C. Moreover, several endotherms were obtained before the final isotropization for a sample of PTEB annealed at 85°C for 12 days, i.e., PTEB shows enantiotropic behavior. The different endotherms may arise from polymorphism or melting-recrystallization phenomena [30]. 

F. Three-stage (partial melting, recrystallization, and total melting) phase transition theory... 

Variable temperature (-150° to +350°) chemical shift spectra have been obtained for melt-recrystallized samples of PTFE. The NMR spectra were acquired using the REV-8 sequence which consists of a long train of closely spaced, high power rf pulses of fixed width, and varying in phase in a cyclical fashion. The cycle consists of eight ir/2 pulses. The total cycle time used was 43.2 psec with a shortest spacing between pulses of 3.6 usee. The nominal resonance frequency was 84.6... 

Figure 5. F-19 REVS chemical shift lineshapes of melt recrystallized PTFE at...

Figure 7. Temperature dependence of the rate of rotational diffusion about the chain axis of PTFE molecules in the crystalline regions of melt-recrystallized samples. Ex = 48 11 kcal/mot.

Figure 9. Temperature dependence of the T, and T, BKI relaxation times of a 68% crystalline melt-recrystallized PTFE sample ( ) denote the short-relaxationtime component in a double exponential decay. T,times longer than 100 ms and Ttimes longer than 1 s are not shown since their experimental values could not be determined accurately. The expected temperature dependence below...

The chemical shift lineshape changes observed for the crystalline fraction of melt-recrystallized PTFE from /L14°C to w28°C (Figure 6) are due to reorientation about an axis essentially parallel to Ozz (which is tilted VL2° from the molecular chain axis). The temperature dependence of the line-shape changes can be simulated as an increase in the rate of rotational diffusion about this axis (Figure 6) and this process has an activation energy of 48+11 kcal/mole. In addition, the... 

More specifically, two melt/recrystallizations were observed, ascribed to conversions to Form 11 and Form 111, respectively, followed by melting of Form 111. However, examination of equivalent samples equilibrated under conditions of elevated humidity using different pan types yielded markedly different results (Figure... 

Details of its properties are summarized in Figure 2. The compound melted at 36°C. It was stable to melting, recrystallization, and distillation. IJj underwent reactions of the carbonyl functionality and had 6.1 x 10 spins/mole. The N-oxyl was reduced with hydrogen on palladium catalyst to the corresponding hydroxylamine. 

M.P. 360C STABLE TO MELTING. RECRYSTALLIZATION. DISTILLATION. REACTIONS OF CARBONYL,... 

Instead, these peaks are frequently caused by extensive recrystallization crystallites that melt, recrystallize and remelt. The chance of early melting happening increases for crystallites that are more imperfect or unstable, and fast cooling is one of the obvious ways to produce such kinds of crystallites. 

An example of the use of a ternary eutectic diagram for the assessment of a melt recrystallization process (for nitrotoluene isomers) is given in section 8.2.1. 

In the present work we address ourselves to two problems directly concerned with determining the physical quantities required for the different extrapolations. The first of these is concerned with the relation of the melting temperature determined by differential calorimetry to the true melting temperature. The other involves an analysis of melting-recrystallization during a DSC scan and its influence on the observed melting temperature. 

The relatively large crystallite thicknesses that were deliberately developed for these dilatometric experiments (12) assured that melting-recrystallization processes did not complicate this particular study of the fusion process. Consequently, none of the well-known effects of melt-recrystallization reported previously... 

The first melting at (1) is incomplete and recrystallizes immediately at (2). The next melting, recrystallization, and renewed melting at (3), (4), and (5) are practically complete, and are followed by partial recrystallization (6) and final melting (7). Quantitative analyses of the various stages of this process using standard DSC baselines are shown in the integral analysis of the heat-flux rates in Fig. A.13.15. This analysis bypasses the nonstationarity problems of the Fourier analysis. 

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