| Abstract: | Wide line NMR spectra of cold drawn poly(ethylene oxide) (PEO) were recorded at temperatures between ?196°C. and 66°C. as a function of the alignment angle between the draw direction and the magnetic field. Line width, second moment, and mobile fraction were determined and are discussed in terms of segmental motion. In agreement with other authors two motional processes were found. (1) The β-process, commencing at temperatures around ?45°C., probably occurs in non-crystalline regions and causes the emergence of a narrow NMR line in addition to the broad one. (2) The β-process was observed between 0°C. and the melting point (66°C.) and led to a pronounced decrease of the width of the broad line and of the second moment. This decrease was anisotropic and was greatest at the alignment angle γ = 45°. As a consequence of this the dependence of the line width and of the second moment on γ is changed: whereas both these quantities show at low temperatures (<0°C.) a maximum at γ = 45° and an absolute minimum at γ = 0°, near the melting point, a minimum close to γ = 45° and an absolute maximum at γ = 0° were found. These changes are explained by oscillations of the helical molecules around their axes in crystalline regions. |
