Fourier-transform Analysis of Models For the Orthorhombic Crystal Phase of the Alternating Ethylene Tetrafluoroethylene Copolymer

Disorder in the relative positions of neighbouring chains in the orthorhombic form of ethylenetetrafluoroethylene (ETFE), which has a polyethylene-like packing in the projection along the c axis, has been studied through a comparison of the observed diffraction profiles on the layer lines with the calculated Fourier transforms of models. The analysis suggests that, along the c axis, integral translational displacements of c/2 are present in the crystals owing to the inclusion of defects in the alternation of the comonomers. On the basis of the analysis, an approximate evaluation of the amount of constitutional defects included in this crystal structure has been attempted. In the crystalline phase, associated with this kind of constitutional disorder, large nearly random translational displacements are present; correlations in relative positions do not go much beyond the first neighbours.