55 - APPLICATIONS OF THE ELECTRON DIFFRACTION METHOD TO THE STUDY OF POLYMER STRUCTURES

Abstract

ABSTRACT The application of electron diffraction methods to the study of the crystalline structure of polymers is discussed in this paper. As an example, the unit cells of isotactic poly-alpha-butene, of isotactic polystyrene and of syndiotactic 1,2-polybutadiene, are obtained from the corresponding electron diffraction spectra. It is observed that, in the study of polymer structures, the electron diffraction method can be performed rapidly. It gives results, which can be interpreted very easily and moreover, in the case of fibre spectra, it gives an undistorted representation of the reciprocal lattice. This allows one to draw important and immediate conclusions as far as the chain structure of the examined product is concerned, by studying the Fourier transform of each polymer molecule. We did so with regard to polyvinylisobutylether and to other isotactic polymers. The differences existing between the intensities, as revealed by the X-ray spectra and the electron diffraction spectra, permit the observation of some interesting facts on the position of the hydrogen atoms, which show a diffraction factor higher for electrons than for X-rays (in comparison with carbon atoms). Finally, the study of the orientation of crystals in thin films is very important both for the study of the mechanism of spherulite formation and to obtain supplementary data derived from an X-ray fibre spectrum; they are well suited to give indices to the reflections; therefore, an exact determination of the elementary unit cell is possible.