Glass transition temperature nuclear magnetic resonance

Richardson, S.J. 1989. Contribution of proton exchange to the oxygen-17 nuclear magnetic resonance transverse relaxation rate in water and starch-water systems. Cereal Chem. 66, 244-246. Richardson, M.J. and Saville, N.G. 1975. Derivation of accurate glass transition temperatures by differential scanning calorimetry. Polymer 16, 753-757. 

The glass-transition temperatures for solution-polymerized SBR as well as ESBR are routinely determined by nuclear magnetic resonance (nmr), differential thermal analysis (dta), or differential scanning calonme-... 

To fully understand the performance of amorphous materials, it is necessary to be able to measure the molecular mobility of the samples on interest. This is because at temperatures as far as 50 K below the glass transition temperature, pharmaceutical glasses exhibit significant molecular mobility that can contribute to both chemical and physical instability.The main techniques that have been developed for monitoring molecular motions in amorphous materials are nuclear magnetic resonance (NMR) and calorimetric techniques (e.g., DSC and isothermal microcalorimetry). Average molecular relaxation times and relaxation time distribution functions obtained from these... 

Methods for determining the presence, kind, and amount of configurational base units can be classified as relative or absolute. Absolute methods do not require calibration with polymers of known tacticity. Relative methods, on the other hand, require comparison with standard substances. X-ray crystallography, nuclear magnetic resonance, infrared spectroscopy, and optical activity measurements are all absolute methods. Relative methods include crystallinity, solubility, glass transition temperature, and melting temperature measurements as well as chemical reactions (Table 3-2). 

In 1956 Thompson and Woods reported that dynamic experiments in extension indicated that orientation increased the temperature of the p transition, about 80°C, for oriented crystalline fibres, and reduced the drop in modulus occurring at higher temperatures. Subsequently nuclear magnetic resonance was used to demonstrate that orientation reduced molecular mobility above the glass transition temperature. Measurements of dynamic extensional and torsional moduli of hot stretched filaments and films were reported in 1963 by Pinnock and Ward, who found that the relations between measured compliances below the glass transition temperature were consistent with the deformation of an incompressible elastic solid. 

In the majority of cases the compatibility of the polymers is characterized by the glass-transition temperature Tg, determined by methods such as dilatometry, differential scanning calorimetry (DSC), reversed-phase gas chromatography (RGC), radiation thermal luminescence (RTL), dynamic mechanical spectroscopy (DMS), nuclear magnetic resonance (NMR), or dielectric loss. The existence of two... 

There have been a number of not particularly successful attempts to correlate asphalt physical properties to chemical properties, including SEC (10,19,35-40). Chollar et al. (41) attempted to relate a number of chemical and physical properties, including percentage LMS, with poor results. Huynh et al. (42) divided asphalt into a number of fractions by preparatory SEC and showed that the glass transition temperature (not precisely defined for asphalts), in moving from one fraction to the next, first decreased with increasing molecular size and then increased. Beazly et al. (43) used SEC and nuclear magnetic resonance (NMR) to estimate asphalt yields and viscosity from crude oil Woods et al. (44) used SEC fractions to study differences in maltenes from tar sand bitumens. 

The numerical value of the glass-transition temperature depends on the rate of measurement (see Section 10.1.2). The techniques are therefore subdivided into static and dynamic measurements. The static methods include determinations of heat capacities (including differential thermal analysis), volume change, and, as a consequence of the Lorentz-Lorenz volume-refractive index relationship, the change in refractive index as a function of temperature. Dynamic methods are represented by techniques such as broad-line nuclear magnetic resonance, mechanical loss, and dielectric-loss measurements. Static and dynamic glass transition temperatures can be interconverted. The probability p of segmental mobility increases as the free volume fraction / Lp increases (see also Section 5.5.1). For /wlf = of necessity, p = 0. For / Lp oo, it follows that p = 1. The functionality is consequently... 

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