Differential scanning calorimetry and

The thermal glass-transition temperatures of poly(vinyl acetal)s can be determined by dynamic mechanical analysis, differential scanning calorimetry, and nmr techniques (31). The thermal glass-transition temperature of poly(vinyl acetal) resins prepared from aliphatic aldehydes can be estimated from empirical relationships such as equation 1 where OH and OAc are the weight percent of vinyl alcohol and vinyl acetate units and C is the number of carbons in the chain derived from the aldehyde. The symbols with subscripts are the corresponding values for a standard (s) resin with known parameters (32). The formula accurately predicts that resin T increases as vinyl alcohol content increases, and decreases as vinyl acetate content and aldehyde carbon chain length increases. 

Common examples of the high Tg macromers are based on polystyrene or polymethylmethacrylate (PMMA) polymers of sufficiently high molecular weight to have a high T (typically on the order of 70-100°C as measured by differential scanning calorimetry) and also to make them immiscible with the acrylic polymer backbone once the solvent or heat has been removed. Typical molecular weight of the polystyrene or PMMA macromers is on the order of 5000-10,000 Da. Their generic structure can be pictured as in Fig. 13 (shown there for polystyrene). 

Reactive compatibilization of engineering thermoplastic PET with PP through functionalization has been reported by Xanthos et al. [57]. Acrylic acid modified PP was used for compatibilization. Additives such as magnesium acetate and p-toluene sulfonic acid were evaluated as the catalyst for the potential interchange or esterification reaction that could occur in the melt. The blend characterization through scanning electron microscopy, IR spectroscopy, differential scanning calorimetry, and... 

Wokaun s group (Lippert et al., 1992) showed, on the basis of thermostability data (differential scanning calorimetry) and H NMR exchange measurements that the n-electron distribution in l-aryl-3,3-dialkyltriazenes (13.10a) indicates that there is a contribution from the 1,3-dipolar mesomeric structure 13.10b. 

The photostability of two polymorphs of nicardipine hydrochloride have been studied using a number of techniques [95]. After irradiation, the drug substance decomposes to a pyridine derivative, and the photodegradation of the /1-form exceeded that of the x-form. It was also found that the color of the two different forms differed with the polymorphic state, but that grinding the two forms lessened the difference in their photochemistries. A correlation between the heat of fusion (measured by differential scanning calorimetry) and the photodegradation rate constant was observed. 

Investigations for the occurrence of polymorphism have been undertaken by ir spectroscopy, differential scanning calorimetry and x-ray powder diffraction (Guinier-de Wolff). No polymorphism has been observed so far. An amorphous form may be prepared artificially by rapid evaporation of a methanolic solution of the drug substance. 

Snee, T. J., "Incident Investigation and Hazard Evaluation Using Differential Scanning Calorimetry and Accelerating Rate Calorimetry," J. Occupational Accidents, 8 (1987). 

Where the consequences of combining two or more materials under given conditions of temperature, confinement, etc., are unknown and cannot be predicted with certainty, testing may need to be performed to screen for potential incompatibilities. Two common test methods used for this purpose are differential scanning calorimetry and mixing cell calorimetry (described later in this section). 

In order to learn about the phase states adopted by LPS and lipid A, Fourier-transform infrared spectroscopy, differential scanning calorimetry, and X-ray small-angle diffraction with CuXa or synchrotron radiation have been applied. In the following section, some recent results are summarized. 

Define thermal analysis, differential thermal analysis, differential scanning calorimetry, and ther-... 

Characterization. Differential scanning calorimetry and thermal mechanical analysis data were obtained on a DuPont 990 thermal analyzer coupled with a DuPont DSC or TMA cell. Isothermal aging studies were carried out with an automatic multisample apparatus. 

Bombardier, H., P. Wong, and C. Gicquaud. 1997. Effects of nucleotides on the denaturation of F actin a differential scanning calorimetry and FTIR spectroscopy study. Biochem Biophys Res Commun 236 798-803. 

Zaiss, K. and R. Jaenicke. 1999. Thermodynamic study of phosphoglycerate kinase from Thermotoga maritima and its isolated domains reversible thermal unfolding monitored by differential scanning calorimetry and circular dichroism spectroscopy. Biochemistry 38 4633 -639. 

Kohyama, K. and Sasaki, T. (2006). Differential scanning calorimetry and a model calculation of starches annealed at 20 and 50 °C. Carbohydr. Polym. 63, 82-88. 

Riga, A. and Collins, R. (2000). "Differential Scanning Calorimetry and Differential Thermal Analysis. Encyclopedia of Analytical Chemistry.". John Wiley and Sons, London. 

Brack, H.-P, Ruegg, D., Biihrer, H., Slaski, M., Alkan, S. and Scherer, G. G. 2004. Differential scanning calorimetry and thermogravimetric analysis investigation of the thermal properties and degradation of some radiation-grafted films and membranes. Journal of Polymer Science Part B Polymer Physics 42 2612-2624. 

Table 2. Differential Scanning Calorimetry and Polarizing Microscopy of Polyols...

A variety of techniques have been used to determine the extent of crystallinity in a polymer, including X-ray diffraction, density, IR, NMR, and heat of fusion [Sperling, 2001 Wunderlich, 1973], X-ray diffraction is the most direct method but requires the somewhat difficult separation of the crystalline and amorphous scattering envelops. The other methods are indirect methods but are easier to use since one need not be an expert in the field as with X-ray diffraction. Heat of fusion is probably the most often used method since reliable thermal analysis instruments are commercially available and easy to use [Bershtein and Egorov, 1994 Wendlandt, 1986], The difficulty in using thermal analysis (differential scanning calorimetry and differential thermal analysis) or any of the indirect methods is the uncertainty in the values of the quantity measured (e.g., the heat of fusion per gram of sample or density) for 0 and 100% crystalline samples since such samples seldom exist. The best technique is to calibrate the method with samples whose crystallinites have been determined by X-ray diffraction. 

The heat of polymerization can be measured accurately by differential scanning calorimetry and is directly related to conversion. Other techniques that have been used include light... 

Microwave spectroscopy indicates that aromaticity diminishes in the order 1,2,5-thia-diazole > thiophene > l,3,4-thiadiazole> l,2,5-oxadiazole> 1,2,4-oxadiazole <84CHEC-1(4)545, B-85MI 410-01>. The aromaticity of heterocycles has been discussed by Katritzky and Barczynski (90JPR885) and by Bird <94H(37)249>. The thermal stability of 2,5-substituted thiadiazoles (23) was studied by differential scanning calorimetry and shown to increase as the rt-contribution of the substituents becomes greater <89MI410-01>. 

Eldem T., Speiser P, and Altdorfer H., Polymorphic behavior of sprayed hpid micropellets and its evaluation by differential scanning calorimetry and scaiming electron microscopy, Pharm. Res., 8, 178, 1991. 

Differential Scanning Calorimetry and NMR Studies on the Water—Sodium Lignosulfonate... 

Two papers reported powder pattern crystallographic results. The paper by Santos et al. (7) stood out from the rest because it presented a collection of more classical physical chemistry experiments. In this paper the authors described the use of micro-combustion calorimetry, Knudsen effusion to determine enthalpy of sublimation, differential scanning calorimetry, X-ray diffraction, and computed entropies. While this paper may provide some justification for including bomb calorimetry and Knudsen cell experiments in student laboratories, the use of differential scanning calorimetry and x-ray diffraction also are alternatives that would make for a crowded curriculum. Thus, how can we choose content for the first physical chemistiy course that shows the currency of the discipline while maintaining the goal to teach the fundamentals and standard techniques as well ... 

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