An infra-red spectroscopic study of molecular orientation and conformational changes in poly(ethylene terephthalate)

Abstract

Polarized infra-red (i.r.) spectroscopy has been used to study the changes in molecular orientation and conformation which occur on drawing poly(ethylene terephthalate) sheets. The i.r. data provided orientation functions 〈 P 2( θ)〉 ir where θ is the angle between the molecular chain axis and the draw direction for these uniaxially oriented sheets. Excellent agreement was obtained between the i.r. orientation functions for absorption bands associated with benzene ring mode vibrations, and orientation functions obtained from optical birefringence. Infra-red orientation functions for absorption bands associated with the trans and gauche conformations of the glycol residue, were then combined with i.r. estimates of the trans/gauche concentrations to examine the changes occurring in drawing. For drawing at 80°C up to a draw ratio of about 3·5, there was good agreement with expectations based on the deformation of a rubberlike network.