AbstractThe absorption intensity of a given infrared absorption band, in the infrared spectrum of an oriented polymer is composed of an orientation and a structural factor. A method is discussed, using polarized infrared radiation, which will measure the contribution of each. The ethylene glycol linkage of the polyethylene terephthalate molecule may exist in either of two forms. These forms are rotational isomers. The trans form of the molecule is the extended form, the gauche form is the relaxed form. The amorphous regions of polyethylene terephthalate films have been found to contain both of these isomers. Polymer orientation is summarized in terms of transition moment types. Orientation parameters characteristic of polyethylene terephthalate films are defined.