Polyethylene‐structure, crystallinity and properties

Abstract By polymerizing ethylene under various conditions of temperature and pressure a wide range of polymers may be made including oils, greases, soft and hard waxes and plastics both softer and harder than the familiar type of polymer used for electrical insulation and film. Some of these variations in properties are caused by changes in average molecular weight. Variations among samples of the same molecular weight are, however, observed; these cannot normally be attributed to changes in distribution of molecular weight but are due to differences in the structure of the polymer molecule. Many of the properties of the solid polymer are determined by the degree of crystallinity. This is affected little by average molecular weight and distribution of molecular weights, but is dependent to a major extent by the degree of chain branching. The measurement of chain branching and its effect on crystallization is discussed and the influence of average molecular weight and molecular structure on a number of properties, including cracking in organic liquids, is described. The importance of the arrangement of the crystalline regions is stressed.