RF-driven and proton-driven NMR polarization transfer for investigating local order

Abstract

Abstract A comparative study of proton-driven and radio-frequency-driven polarization-transfer processes in NMR of rare spins is presented in view of investigating order in partially disordered solids. The results exemplify the complementary use of the two techniques: proton-driven polarization transfer for recording quasi-equilibrium spectra that characterize long-range order, and radio-frequency-driven transfer for the measurement of geometrical rate factors from which information about local order is obtained. Procedures are described for the evaluation of polarization-transfer data. The techniques are applied to the study of order in amorphous samples of atactic polystyrene and syndiotactic poly(methyl methacrylate). In polystyrene, orientational correlation among the phenyl groups is found within a range of 5 Å. In poly(methyl methacrylate), local order is below the detection limit.