Third phase in poly(ethylene terephthalate)

The concept of the oriented amorphous phase, which is also known as the intermediate or third phase, is discussed and a method is outlined for measuring it. It is suggested that the two phase models of polymer structure, which ascribe partial orientation to the amorphous regions, are in fact close to the three phase models, because the amorphous orientation factor and the third phase are representative of the same parameter, i.e. orientation in the amorphous phase.