Carbon-13 NMR of Polymers

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Abstract
Recent advances in 13C NMR spectroscopy instrumentation are causing an almost-explosive flurry of activity in organic molecular structure studies. This is the most powerful molecular structure tool to come upon the scene since proton NMR, and it will undoubtedly surpass the latter in importance. There are several reasons for this: (a) The l3C chemical shifts cover a range of about 300 ppm compared to only about 12 ppm for proton chemical shifts, i.e., there are more “boxes” in which to display the same information (b) 13C chemical shifts are much more sensitive to steric environment than proton chemical shifts. Thus two carbon nuclei whose local environments are comparable might have relatively large chemical shift differences. These shift differences depend primarily upon the local π-electron density, whereas proton shifts are more strongly influenced by neighboring bond anisotropy shielding effects [1,2]. (c) 13C spectra are simpler to interpret because all spin-spin interactions can be removed by heteronuclear decoupling. (d) Dipolar broadening of peaks, characteristic of proton polymer spectra, is very much reduced in 13C polymer spectra, even in solid samples.