MOBILITY OF SIDE-CHAINS IN POLY(DIETHYLPHOSPHAZENE) AS STUDIED BY H-1C-13/N-14 TRIPLE-RESONANCE SOLID-STATE NMR/

The existence of three polymorphs of poly(diethylphosphazene) has rece ntly been established by MAS NMR and X-ray diffraction characterizatio n. In the present work, the mechanism of motion of the ethyl side grou ps in the high-temperature modification of poly(diethylphosphazene) is identified and compared to the arrangement of side groups in the low- temperature modification. For this purpose, a rotor-synchronized tripl e resonance NMR experiment, called TRAPDOR, was applied for the qualit ative evaluation of the average distances between carbons and nitrogen s in the polymorphs. The agreement between these qualitative average d istances and the molecular modeling supports the hypothesis that the e thyl groups undergo a complete rotation about the P-CH2 bond in the hi gh-temperature modification.