Ultraslow molecular motions in crystalline polyoxymethylene. A complete elucidation using two-dimensional solid state NMR.
The slow magic angle spinning 2D exchange NMR expt. applied to semicryst. polyoxymethylene shows the existence of ultraslow mol. rotations in cryst. regions of the material. Simulation of the 2-dimensional spinning sideband spectra, which are characteristic for the mol. motion involved, shows that a rotation of the polyoxymethylene helical chains over 200 Deg is responsible for the obsd. spectra. The activation energy is 20 kcal/mol, in good agreement with values obtained for the a relaxation in dynamic mech. and dielec. studies.
Dieser Eintrag ist freigegeben.