FOURIER-ANALYSIS OF POLYMER X-RAY-DIFFRACTION PATTERNS

While x-ray diffraction has proven to be extremely useful for the study of semicrystalline polymers, considerable confusion exists regarding interpretation of the line shapes of the diffraction peaks. Although it is generally agreed that macromolecules form small and imperfect crystallites, there is no accepted method for analyzing the peak profiles of the diffraction pattern. In analyzing the shapes of diffraction peaks from polymers, it has been mistakenly assumed that it is possible to distinguish between models based on ″microstrains″ and on paracrystallinity. It is shown that either paracrystallinity or distortions due to dislocations give rise to disorder of the second kind and cannot be distinguished by current diffraction methods. Fourier analysis of shapes of peaks from polymers gives quite satisfactory results, despite comments in the literature to the contrary. The analysis can now be carried out with single peaks; multiple orders are not required.