A study of molecular orientation in one-way drawn poly(ethylene terephthalate) films by means of polarized infra-red spectroscopy and birefringence measurements

Summary Polarized infrared spectroscopy and birefringence measurements have been used to study the changes in molecular orientation which occur on homogeneous hot (T=80°C) and cold (T=20°C) drawing of poly(ethylene terephthalate) (PET) sheets. Excellent agreement was obtained between the infrared orientation functions for absorption bands associated with 1507 cm^–1, 1580 cm^–1 and 1615 cm^–1, C-C stretching mode of the benzene ring, and average orientation functions obtained from optical birefringence. It was confirmed that the Gauche conformer of the ethylene glycol residue in the amorphous phase could be oriented perpendicularly to the draw direction (_p<4). The development of molecular orientation along the specimen axis in the necked sample confirms the entangled nature of the polymer chains in which the natural draw-ratio corresponds to the response of a network stretched up to its maximum of extensibility.