Spectroscopic and chemical-shift selective imaging

Uniaxial drawing of polymer samples introduces a uniaxial distribution of molecular orientations which often can be approximated by a Gaussian. The NMR spectrum then depends on the angle between the drawing direction and the magnetic field. For example, the spectrum of unoriented FIFE is well approximated by a symmetric powder pattern (Fig. 10.3.1(a), cf. Fig. 3.1.3), while the spectrum of a uniaxially oriented sample exhibits two peaks when the direction of molecular order is parallel to the magnetic field (Fig. 10.3.1(b)) [Hepl]. 

Because F is an abundant nucleus in PTFE, both anisotropic chemical shift and dipole-dipole interactions are present in the sample. The homonuclear dipolar 

Chemical-shift selection The homonuclear dipole-dipole interaction among the abundant nuclei needs to be eliminated by use of a multi-pulse sequence like MREV8. Such 

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Spectroscopic and chemical-shift selective imaging of polymers... 

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