Structural study of phase transition behavior of uniaxially-oriented ethylene-tetrafluoroethylene alternating copolymer

Crystal modifications and phase transition behavior have been investigated for the uniaxially-oriented ethylene-tetrafluoroethylene alternating copolymer samples of equimolar content by the temperature-dependent X-ray diffraction and Raman spectral measurements. The X-ray fiber diagram measured for the sample drawn at 0 degrees C has been found to be quite different from that drawn above 100 degrees C or the normal orthorhombic-type sample. The new X-ray diagram is characterized by the sharpness of the reflections and the positional shift from the horizontal lines, indicating the tilting phenomenon of the crystallites. This sample was found to transform into the hexagonal phase in the temperature region around 110 degrees C with keeping the tilting phenomenon. The molecular motion of the more or less conformationally disordered chains was enhanced above this transition region as seen from the increase in the half-width of trans bands and the intensity increment of gauche bands in the Raman spectra.