Nuclear magnetic resonance molecular orientation

Quasielectric Light Scattering and Order Fluctuations in the Isotropic Phase 174 Nuclear Magnetic Resonance and Order Fluctuations in the Isotropic Phase. 175 Quasielastic Light Scattering and Orientational Fluctuations below Tc. . . 177 Nuclear Magnetic Resonance and Orientational Fluctuations below Tc.. .. 177 Optical Kerr Effect and Transient Laser-Induced Molecular Reorientation.. 181... 

In this review the definition of orientation and orientation functions or orientation averages will be considered in detail. This will be followed by a comprehensive account of the information which can be obtained by three spectroscopic techniques, infra-red and Raman spectroscopy and broad line nuclear magnetic resonance. The use of polarized fluorescence will not be discussed here, but is the subject of a contemporary review article by the author and J. H. Nobbs 1. The present review will be completed by consideration of the information which has been obtained on the development of molecular orientation in polyethylene terephthalate and poly(tetramethylene terephthalate) where there are also clearly defined changes in the conformation of the molecule. In this paper, particular attention will be given to the characterization of biaxially oriented films. Previous reviews of this subject have been given by the author and his colleagues, but have been concerned with discussion of results for uniaxially oriented systems only2,3). 

In this review recent theoretical developments which enable quantitative measures of molecular orientation in polymers to be obtained from infra-red and Raman spectroscopy and nuclear magnetic resonance have been discussed in some detail. Although this is clearly a subject of some complexity, it has been possible to show that the systematic application of these techniques to polyethylene terephthalate and polytetramethylene terephthalate can provide unique information of considerable value. This information can be used on the one hand to gain an understanding of the mechanisms of deformation, and on the other to provide a structural understanding of physical properties, especially mechanical properties. 

The perpendicular orientation of the rings of 3,5-diiodothyronines, which was postulated from molecular models, has been confirmed by x-ray crystallographic studies (102), molecular orbital calculations (103), and nuclear magnetic resonance studies (104,105). 

Another technique which is of considerable importance in determining orientation in polymers is broad line nuclear magnetic resonance. In a solid polymer at low temperatures when molecular motions are quenched. 

Wide angle X-ray scattering was used to examine crystallite orientation, small angle scattering to determine the orientation of any lamellar structure, infra-red dichroism to study the orientation of non-crystalline regions, and nuclear magnetic resonance to record molecular mobility. 

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. 

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