Structural disorder in the α form of isotactic polypropylene

A detailed analysis of the Bragg as well as of the diffuse X-ray diffraction scattering of isotactic polypropylene (i-PP) fiber samples, suitably crystallized in the α form under different conditions, is reported. A limit-ordered (α2 form) and a limit-disordered (α1 form) model structure have been described to account for the features of the experimental X-ray diffraction profiles of i-PP samples prepared in the α form. The disorder consists of the statistical occupation of the lattice sites of isomorphous helices having opposite up/down orientations. Depending on the conditions of crystallization, intermediate-disordered modifications between the limit-ordered and the limit-disordered, can be obtained. The analysis of the Bragg contribution to the X-ray diffraction scattering of isotactic polypropylene samples crystallized in the α form provides direct quantitative information regarding the amount of up/down disorder, whereas the analysis of the diffuse scattering subtending the Bragg reflections in the ...