X-RAY-INVESTIGATIONS OF BINARY SOLID-SOLUTIONS OF N-ALKANES AS MODEL-SYSTEMS FOR EXTENDED CHAIN CRYSTALS OF POLYETHYLENE

Solid solutions of the binary systems n-dotriacontane/n-octacosane and n-octacosane/n-tetracosane have been investigated by means of powder techniques, including measurements of relative intensities of the strongest 14 reflexion groups. The samples exhibited mainly orthorhombic crystal structure, the n-alkane molecules crystallized in layers in all-trans conformation. The solutions of n-C28H58/n-C24H50 showed fractionation into different phases at room-temperature. For the solutions of n-C32H58/n-C28H58 comparison of the measured relative intensities with computed intensities, using two alternative structure models, indicate that the two components of the solution are randomly distributed within the lamellae lateral to the molecular axes. The defect structure of the surface regions can be described by assuming nematical shifts of the shorter molecules by 2.54 Å with respect to the centre of the lamellae. The results obtained from these model-systems are interpreted with respect to the multicomponent systems of lineat polyethylene crystallized appropriately into extended chain crystals. Beside the observation, that fractionation into lamellae of different mean thicknesses occurs, quantitative models for the structure of the longitudinal boundary regions are achieved. © 1979 Dr. Dietrich Steinkopff Verlag.