A theoretical analysis of coupled relaxation processes has been used in the quantitative interpretation of carbon-resolved, proton TI, data obtained at 15.1 MHz for a variety of solid blends of poly(pheny1ene oxide) and polystyrene. This analysis permits an estimate of spin-diffusion rates between different chemical species. These rates are strongly dependent on spatial proximity and hence are applicable to the determination of the homogeneity of the blends. Proton Tl,'s in the blends are nearly but not quite averaged to a single value by spin diffusion, indicating extensive intermixing of poly(pheny1ene oxide) and polystyrene chains. The proton TI, experiments are sensitive enough to distinguish between identically prepared blends made from poly(pheny1ene oxide) and either atactic or isotactic polystyrenes. While the bulk of both types of blends is an intimate mixture of polymer chains, there are also some small regions in the atactic polystyrene blend where the polystyrene is not uniformly dispersed.

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The amplitudes of ring-and main-chain motions of a variety of polystyrenes have been established from the 13C NMR magic-angle spinning sideband patterns of dipolar and chemical shift tensors. The frequencies of the same motions have been determined by 7\(C) and Tlp(C) experiments. The most prevalent motion in these polymers is restricted phenyl rotation with a sizable average jump angle. Both the amplitude and frequency of this motion vary from one substituted polystyrene to another and from site to site within the same polystyrene. A small fraction of sites within some of the polystyrenes permits high-frequency (megahertz) ring flips in combination with main-chain rotational reorientation, also at high frequency. The concentration of these sites does not depend upon intrachain conformational or configurational defects but rather is determined by interchain glassy-state packing. Low-frequency (kilohertz) main-chain motion is insensitive to ring substitution for some of the polystyrenes, suggesting the presence of a cooperative motion in which the rings only translate as the main chain rotates.

Experimental cross-polarization transfer rates, from protons in the local dipolar field to carbons in an applied radio-frequency field, can be used to determine quantitatively the relative contributions of spin-lattice and spin-spin processes to carbon Tlp relaxation. We show that this procedure is to be preferred to determinations based either on various semiquantitative arguments, on the analysis of the Hi dependence of Tlp, or on the use of theoretically calculated rigid-lattice spin-spin transfer rates. We find that average carbon Tip's (near 35 kHz) for a wide variety of glassy polymers at room temperature are predominantly spin-lattice (motional) in character.