When isotactic polypropylene a form was annealed at high temperatures, a structural transition from a disordered state to an ordered state was observed and studied by X-ray diffraction. The space groups of the two forms were proved to be C2/c and P2ifc respectively. We proposed an "order domain eduction model" for the transition, from an analysis of reflected intensity and line width. The structure factor of the intermediate state was then written Fint=nFc21c +(l-n)FP21/c where n is the volume fraction of the C2/c form; this gave a good value of the Rfactor, 0.152. From structural considerations, the transition was interpreted as the arrangement of CH-CH3 bonds (upward or downward) changing into complete order, where the helical arrangement was already in complete order in both forms; reasons for this model were discussed using energy considerations. The origins of streak-like diffuse scattering and of various disorders in the crystal were also discussed.

Plastic deformation processes in oriented polyethylene are investigated by the X-ray method, and changes in texture produced by transverse compression are interpreted in terms of twinning, slip and phase transformation. The crystal structure of the new form produced by the phase transformation is determined, and the unit cell is a monoclinic one with a=8.09, b=2.53, c=4.79 Å and β=107.9°. The phase transformation is considered to be of diffusion-less type and a transition mechanism similar to that of twinning is proposed.

ABSTRACT:Morphology of cold drawn poly(ethylene terephthalate) (PET) was studied by the X-ray diffraction method. In slowly drawn PET, paracrystalline reflections were observed at an early stage of crystallization by annealing, and it was found that the paracrystalline structure was basically monoclinic. In the case of annealing at temperatures below 100°C, the crystalline structure became triclinic after passing through the paracrystalline state. Tilting of the crystalline c-axis (molecular axis) was seen in the course of the transition from the paracrystalline to the triclinic state. At higher annealing temperatures, the triclinic crystallites were sufficiently developed to form crystalline layers in which the molecular chains were tilted in directions which depended on the inclination of the layers.In the case of rapid drawing, strain-induced crystallization occurred, but paracrystalline reflections were not observed. In the rapidly drawn sample, tilt of the c-axis was small, while inclination of the layer was large.

No abstract

No abstract