Observation of 1H nuclei in heterogeneous solids via cross-polarization 13C N.M.R.

The complementary advantages of high sensitivity and high chemical shift dispersion offered by 1H and 13C spins are exploited in experiments designed for indirect observation of the proton system through 13C resonances. Pulse sequences devised for indirect measurements of proton T 2 relaxation times and for indirect observation of proton spin diffusion (an extension of the Goldman-Shen experiment) are presented and compared to direct proton measurements. A proper image of the structural heterogeneity, manifested by three distinct physical regions, is deduced from indirect measurements on static and rotating samples of polyoxymethylene. The results are used as a model for illustrating the potential of the proposed sequences. Possible restrictions on the quantitative analysis of the extent of the different morphological regions are discussed in terms of their different cross-polarization characteristics.