Determination of molecular orientation in poly(ethylene terephthalate) by means of 2H nuclear magnetic resonance

Abstract

The molecular orientation in poly(ethylene terephthalate) (PET) drawn by necking was studied before and after crystallization by 2H nuclear magnetic resonance (n.m.r.) and by wide-angle X-ray scattering (WAXS) pole figures. In order to determine separately the orientation of the benzene ring and of the ethylene groups, the n.m.r. investigations were performed on samples in which only the benzene ring was deuterated as well as on samples in which only the ethylene groups were deuterated. By applying different ‘waiting times’ in the n.m.r. measurements, it was also possible to determine separately the orientation of chains of different mobilities. Thus, more detailed and more complete information on molecular orientation is obtained by n.m.r. than by WAXS. As far as a comparison was possible, agreement between n.m.r. and WAXS was obtained. In addition, the n.m.r. results show that, for example, a parallelization of the planes of the benzene rings occurs not only in the crystals but also in the amorphous regions, and that the ethylene groups are oriented to a smaller degree in the draw direction than the benzene ring parts of the chain.