STRUCTURAL TRANSITIONS OF POLYETHYLENE STUDIED BY POSITRON-ANNIHILATION

Two kinds of polyethylene samples, low-density polyethylene and high-density polyethylene, have been studied using positron lifetime measurements in the temperature range from 96 to 370 K Glass transitions and other secondary transitions are observed and the glass transition temperatures are determined. It has been found that the orthopositronium lifetime and its intensity are sensitive to the transitions and the number of free-volume holes reaches a minimum near the glass transition temperature T(g). The molecular motions, the structural transitions and the crystallinity effects are discussed in terms of the properties of the free volume.