INDEX Calorimetry

Solution Polymers. Acryflc solution polymers are usually characterized by their composition, solids content, viscosity, molecular weight, glass-transition temperature, and solvent. The compositions of acryflc polymers are most readily determined by physicochemical methods such as spectroscopy, pyrolytic gas—liquid chromatography, and refractive index measurements (97,158). The solids content of acryflc polymers is determined by dilution followed by solvent evaporation to constant weight. Viscosities are most conveniently determined with a Brookfield viscometer, molecular weight by intrinsic viscosity (158), and glass-transition temperature by calorimetry. 

This temperature rise can be detected directly (laser calorimetry and optical calorimetry), or indirectly by measuring the change in either the refractive index (thermal lensing, beam deflection or refraction and thermal grating) or the volume (photo- or optoacoustic methods). This review will focus primarily on photoacoustic methods because they have been the most widely used to obtain thermodynamic and kinetic information about reactive intermediates. Other calorimetric methods are discussed in more detail in a recent review.7... 

It may happen that the properties of a monomer and its oligomers and polymers are so similar that they cannot be separated by precipitation that in the appropriate solvents the reaction mixture gels, so that dilatometry cannot be used that it becomes so opaque that neither refractive index nor optical rotation can be determined and that the reaction is too slow for normal reaction calorimetry. This situation was met when the author attempted to study the polymerisation of trimethyl and tribenzyl laevo-... 

Differential scanning calorimetry Limiting oxygen index w-Cresol... 

A range of heterocyclic azides were studied by differential scanning calorimetry, the enthalpies of thermal decomposition were lower than might have been expected, from 0.3—1 kJ/g. If ortho substituents onto which the azide could cyclise were present, decomposition enthalpies were, as one would expect, lower still [5], as well as the individually indexed compounds ... 

Most of the physical properties of the polymer (heat capacity, expansion coefficient, storage modulus, gas permeability, refractive index, etc.) undergo a discontinuous variation at the glass transition. The most frequently used methods to determine Tg are differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and dynamic mechanical thermal analysis (DMTA). But several other techniques may be also employed, such as the measurement of the complex dielectric permittivity as a function of temperature. The shape of variation of corresponding properties is shown in Fig. 4.1. 

Index Entries Escherichia coli polyhydroxyalkanoates fed-batch fermentation nuclear magnetic resonance differential scanning calorimetry. 

Tan, C. P., Che Man, Y. B., Selamat, J., and Yusoff, M. S. A. 2002. Comparative Studies of Oxidative Stability of Edible Oils by Differential Scanning Calorimetry and Oil Stability Index Methods. Food Chem., 76,385-389. 

The magnitude of the reaction is an index of the potential of a hazard. The screening tests for the magnitude of a reaction include reaction heat calculation, reaction calorimetry and sealed cell differential scanning scanning calorimetry (SC—DSC). 

Many relatively slow or static methods have been used to measure Tg. These include techniques for determining the density or specific volume of the polymer as a function of temperature (cf. Fig. 11-1) as well as measurements of refractive index, elastic modulus, and other properties. Differential thermal analysis and differential scanning calorimetry are widely used for this purpose at present, with simple extrapolative eorrections for the effects of heating or cording rates on the observed values of Tg. These two methods reflect the changes in specific heat of the polymer at the glass-to-rubber transition. Dynamic mechanical measurements, which are described in Section 11.5, are also widely employed for locating Tg. 

Tg can be measured by dilatometry, refractive index, differential scanning calorimetry, dynamic mechanical methods and by dielectric relaxation techniques. 

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