NUCLEAR MAGNETIC-RELAXATION STUDY OF POLY(PROPYLENE OXIDE)COMPLEXED WITH LITHIUM SALT

Measurements of Li-7, H-1 and F-19 nuclear relaxation times and Li-7 linewidths are reported for poly(propylene oxide) complexed with lithium salts (LiClO4, LiBF4 and LiAsF6). For PPO6LiBF4 and PPO8LiClO4 the onset of the Li-7 motional line narrowing, occurs at approximately T-8. The NMR decoupling methods was used to eliminate heteronuclear contribution to Li-7 line shape. It was found that the Li-H interaction accounts for 80-90% of the linewidth. The remarkably similar temperature dependence of the measured H-1 and Li-7 spin-lattice relaxation rates, which shows rate maxima at 340-350 K in this PPO-Li salts complexes, gives additional evidences for correlation between the cationic and the polymeric motions. The nuclear spin-lattice relaxation rates of the PPO complexes always peak at higher temperatures than the POE complexes, suggesting a lower ionic mobility for the former complexes. The frequency dependence of the relaxation rates cannot be described in the framework of the BPP theory.