Scalar decoupled line widths

Figure 4. Scalar decoupled line width as a function of temperature for a, Hytrel 7246 and, b, Hytrel 4056. Key O, central -CH - carbons and , -OCHi-...

Although crosslinked polymers and polymer gels are not soluble, the spectra of swollen, low crosslink density networks exhibit reasonably narrow C-13 NMR line widths, sufficiently resolved to reveal details of microstructure 13S). Thus, recording the spectra under scalar low power decoupling yields characterization information and some dynamic measurements, concerning T, T2 (line widths) and nuclear Overhauser enhancement (NOE) for lightly crosslinked polymers. 

Figure 3. Line widths of the C NMR (50.3 MHz) solid Hytrel scalar decoupled 29 ppm (O) and 73 ppm resonance fOl as a function of average hard block length at 34°C. The temperature below which the line width increases due to dipolar broadening is slightly different for the two types of aliphatic carbons fsee Figure 4). It also increases slightly as the hard segment content of the polymer increases. The -OCHi- line width for the Hytrel 7246 sample was measured at a temperature below this point and therefore does not fall on this line.

The differences in the NMR spectra measured under Fourier Transform conditions with scalar decoupling of the same substance, say water and ice, boggle the mind. The proton NMR spectrum of the water is sharp and narrow with a band width of one Hz, while the proton NMR spectrum of ice is extremely broad with a band width of 20 KHz. This is totally unexpected. In the early days of experimental NMR, the NMR lines of solids were so broad that no measurable signal could be obtained related to chemical structure. 

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