An investigation of molecular orientation in oriented poly(ethylene terephthalate) films

Abstract

Attempts to obtain a quantitative description of molecular orientation in one-way drawn poly(ethylene terephthalate) films are described using a combination of nuclear magnetic resonance (n.m.r.), optical and X-ray diffraction measurements. Complete theoretical developments are presented for the anisotropy of the n.m.r. second moment and for the optical anisotropy. The n.m.r. method shows severe limitations, primarily due to its inability to deal with the preferred orientation situation and to a lesser extent to the complications due to the presence of gauche conformations of the glycol residue. It has been shown, however, that the optical anisotropy is consistent with a simple scheme for the development of orientation during drawing. In this scheme a molecular chain axis undergoes the directional change of a line in the macroscopic body lying in the same direction, and preferred orientation is introduced by a simple mathematical approximation, which appears to hold well at high draw ratios.