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Methods are described for determining the mutual orientation of molecular interaction tensors based on twodimensional NMR powder spectra. Necessary conditions are derived under which this determination can be made, procedures for the computation and analysis of 2D powder spectra are indicated, and a technique for the construction of ridge plots is worked out. Chemical shift resolved dipolar powder spectra provide an easily interpreted representation of the mutual orientation of chemical shielding and dipolar coupling tensors. The various features and practical applications of such spectra are demonstrated with 2D powder spectra of benzene, lead formate. and methyl formate.It is sufficient to consider a system of two nuclear species, I and S, including Zeeman, dipolar, and possibly quadrupolar interactions. The general Hamiltonian of the system is 1C =JC OI + JC ZI +·JC II + JC IS + JC ss +·JC zs +JCos with the two quadrupolar interaction terms the Zeeman terms and the three dipolar interaction terms

This high-resolution solid-state NMR work explores the usefulness of carbon-carbon nuclear spin diffusion to probe the miscibility of polymer blends. Experiments involving one-and two-dimensional NMR spectra, applied to blends ofpoly(ethylene terephthalate) (PET) and bisphenol-A polycarbonate (BP APC), show that spin exchange occurs between carbon-13 nuclei located in monomer units that belong to the two different homopolymers. Carbon spin diffusion, which strongly depends on the internuclear distance, is explored as a possible probe for specific interactions between polar groups of the two polymers. Our results clearly show that !he PET /BP APe blends studied are homogeneously mixed at distances of 4.5 to 6 A.

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