A convenient and rapid x‐ray diffraction method is described for the determination of per cent crystallinity in polyethylene, using a scanning goniometer with Geiger tube and scaler counter. Results are presented on per cent crystallinities of a number of polyethylenes and on samples made by quenching polyethylene melt at different temperatures in the range of 20–102°C. The samples of polyethylene studied were found to have 65‐71% crystallinity. The temperature at which plyethylene melt is quenched has no appreciable effect on the crystalline content.

A discussion of the methods for studying orientation of crystalline and amorphous regions in polyethylene films is given. Extruded polyethylene films and films after having been stretched approximately 200% were studied by the methods of x‐ray diffraction and absorption of polarized infrared radiation. It is shown that in extruded polyethylene films the a‐axes of the crystallites are oriented parallel to the extrusion direction. The amorphous regions in these are either not oriented or show only to a slight degree the orientation of chains perpendicular to the extrusion direction. When the polyethylene films are stretched, both the crystallites and the amorphous regions become oriented. In stretched films, the orientation of the crystallites is with c‐axis parallel to the stretching direction, and the chains in the amorphous regions are also oriented parallel to the stretching direction. Two mechanisms by which a‐axis orientation may arise during extrusion of polyethylene films, and a convenient method for determining the relative degree of a‐axis orientation in polyethylene films are given. The relative degrees of a‐axis orientation as determined by x‐ray diffraction and dichroism of absorption at 13.70 μ are compared for a number of film samples.

Physical changes which accompany the crystallization of isotactic polypropylenes have been observed by dilatometry and optical microscopy at temperatures between 120 and 160°C. Samples were fused at 220°C. and then held at a predetermined crystallization temperature for times ranging up to many hours. Rate constants for the crystallization were calculated from volume changes and from measurements of radial growth of spherulites. Polypropylenes from different sources exhibited quite different concentrations of spherulites and growth rates. Crystallization appears to proceed, at least at the higher temperatures, by spherical growth from a fixed number of nuclei, apparently arising from foreign matter in the polymer. With decreasing temperature, the number of nuclei (hence also the number of spherulites) increases, since apparently the conditions for nucleation become less critical. The crystallization follows the kinetics of a nucleation‐controlled process according to an Avrami equation, ‐log (1 ‐ ΔV / ΔV ∞) = kt3. Deviations from the third power of time at the lower temperatures may be the result of a secondary ordering process, slower than the primary crystallization.

A microbeam camera has been used in x‐ray diffraction studies of the changes which occur in orientation of crystallites in polyethylene film when the film is stretched and later relaxed. The collimator of the microbeam camera, 100 μ in diameter, allows one to follow the orientation changes very closely in the necked‐down region of a stretched sample. The stretching of polyethylene proceeds by alignment of the a‐axes of the crystallites perpendicular to the stretching direction with the planes containing b‐ and c‐axes perpendicular to the a‐axis but randomly oriented, followed by a gradual change to a state in which the c‐axes become more nearly aligned in the stretching direction although perfect alignment is not achieved. On relaxation, either the orientation of the c‐axis parallel to the original stretching direction becomes less perfect, or folding of the oriented crystallites about the b‐axis takes place. In the latter case the preferred crystallographic directions parallel to the stretching direction have indices such as [u0w]. These orientation changes during stretching and relaxation of the stretched samples suggest that crystallites in polyethylene films consist of parallel arrangements of platelets containing b‐ and c‐axes. The distinction between directions in the reciprocal lattice and the crystal lattice is clarified. A number of x‐ray diffraction patterns and charts of dimensional changes illustrate the paper.

Lanthanum, neodymium, and dysprosium trichloroacetates have been prepared and characterized. Vacuum pyrolysis of the anhydrous salts yields anhydrous metal chlorides.