NMR studies of solid polymers

Department of Chemistry and IRC in Polymer Science and Technology, University of Durham, South Road, Durham DHl 3LE, UK 

It is the intention in this chapter to present an overview of some major aspects of NMR studies of solid polymers and to give some examples of applications. It will also provide the background to the more sophisticated multi-dimensional solid-state NMR techniques discussed in Chapter S. 

NMR studies of solids can be generally grouped into three types (a) broadline spectra (b) relaxation times and (c) high-resolution spectra. 

Of course, spin-spin (transverse) relaxation directly affects the observed signal (free induction decay) from pulsed NMR operation, which is Fourier transformed to yield the spectrum, so that the three areas are not totally distinct This article will address all three aspects but will only relate to H, F and NMR. In particular, there will be no discussion of spectra of polymers, important though that topic is. In suitable circumstances other spin- nuclei such as N, Si and P can be relevant, and they will behave much like 

Following the discovery of the NMR phenomenon in 1945 by two groups of physicists [1,2] NMR was applied to a wide range of systems, both solids and solutions. However, it rapidly became obvious that solution-state NMR was exceptionally useful to chemists because the high resolution achieved (with linewidths for H less than 1 Hz) aUowed small but important effects (i.e. chemical shifts and splittings due to coupling constants) to be observed. Solid-state NMR became for a while the esoteric preserve of a few hardy physicists and physical chemists. This situation became even more apparent after the introduction of the Fourier transform principle made high-quality spectra obtainable. 

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Schaefer, J., High Resolution c nmr Studies of Solid Polymers, "Molecular Basis of Transition Relaxation",... 

In NMR experiments, molecular mobility leads to narrowing of the resonance lines. Conversely, restricted molecular motion, as occurs in crystalline phases, causes line-broadening. Until the advent of magic angle spinning and related techniques, tliis was a hindrance to NMR studies of solid polymers. We have used it to advantage in following the orientation effects in solid PTFE. 

Variable-Temperature Magic-Angle Spinning Carbon-13 NMR Studies of Solid Polymers... 

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