2D-solid state NMR studies of ultraslow motions: phenylflips and chain motions in the glassy state

Abstract

The deuteron 2D exchange NMR experiment was applied to study ultraslow molecular reorientations in polymers below the glass transition. Experimental spectra are presented for phenyldeuterated polycarbonate (PC-d 4) and an ionene polyelectrolyte ([poly-( N, N-dimethylimino)decamethylenetetrafluoroborate] (I-10-Me-BF 4), deuterated in the α-position of the alkylene chain. In PC the phenylflip motion in the glassy state does not involve rotations by exactly 180°. Instead the reorientational angle distribution (RAD) of this local process is rather ill-defined and changes when mechanical stress is applied to the sample. The chain dynamics in the solid polyelectrolyte can be considered as a motion between fixed ends, due to the strong Coulomb interaction of the ionic centres. No evidence is found for trans-gauche isomerization; instead the spectra exhibit the characteristics of a restricted diffusive motion.