Solid-state proton NMR studies of polymers

A considerable amount of valuable information was nevertheless provided by solid state NMR over many years, and the progress of the technique has been charted by periodic reviews of the area [2-5]. In the last decade however, there have been developments that have significantly increased the information that can be extracted. Among these have been the development of a much greater understanding of the way spin diffusion affects the observed relaxation behaviour in heterogeneous systems, and the use of experimental techniques that allow the manipulation and detection of the magnetisation on the basis of chemical shift (either chemical shift or chemical shift via cross-polarisation). These have effectively added a new dimension to the classic relaxation techniques. 

Our intention in this chapter is to provide an overview of the state of the art in solid-state NMR of polymers with particular emphasis on those areas of recent development which we feel are most significant. The work cited reflects this, and does not represent an exhaustive catalogue of the available literature. Our intention throughout has been to attempt to explain the underlying physics in a way that should be accessible to the reader who is not a specialist in solid-state NMR, and for this reason we have occasionally sacrificed theoretical rigour in favour of simplicity of explanation. This should not present a problem since rigorous explanations are available to the interested reader from the original literature and in standard NMR texts. 

The vast majority of solid polymers are heterogeneous, in that they contain regions of different molecular mobility, or regions of different chemical composition, or both (as introduced in chapters 5 and 6). Solid polymer systems that are not heterogeneous in some sense are quite rare, and usually not practically useful because of their poor mechanical properties. 

The intimate nature of the relationship between this heterogeneity and the mechanical properties of the system is related to the motional characteristics of the different regions present in the sample. The practical implications of this are well known and widely used in, for example, block copolymer systems 

The Zeeman interaction of nuclear dipoles with an applied magnetic field ( o) gives rise to the splitting that is the basis of NMR. The energy difference is proportional to the field and the populations of the energy levels conform to a Boltzmann distribution. The next strongest interaction is the one between 

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