SETTING ANGLE OF MOLECULAR CHAINS IN POLYETHYLENE CRYSTALS

The setting angles of chains in solution-grown crystals of paraffins were measured from optical transforms of their electron diffraction patterns. Those of solution-grown, melt-crystallized, and drawn polyethylenes were determined by the x-ray diffraction method. The cell dimensions, paracrystalline disorder, and thickness and size of crystallites of these specimens were measured. From these data, factors increasing the setting angle were found as follows; (1) folding of molecular chains, (2) imperfections of crystal lattice, (3) expansion of cell dimensions and (4) smallness of thickness and lateral size of crystallites. The temperature dependence of the setting angle is also dis-cussed; the higher the temperature, the larger the setting angle. At low temperatures, the setting angle also increases, and the values are compared with those predicted theoretically from the minimization of lattice energy. The temperature dependence of the setting angle is interpreted in terms of a conformational change of the stem segments in the crystalline core. © 1979, Taylor & Francis Group, LLC. All rights reserved.