Elucidation of the chain conformation in a glassy polyester, PET, by two-dimensional NMR
The chain conformation of glassy poly(ethylene terephthalate) (PET) was characterized by two-dimensional double-quantum nuclear magnetic resonance (NMR). In amorphous carbon-13-labeled PET, the statistics of the O-13CH2-13CH2-O torsion angle were determined, on the basis of the distinct shapes of the two-dimensional NMR patterns of trans and gauche conformations. In crystalline PET, the trans content is 100 percent, but in the amorphous PET it is only 14 percent (+/-5 percent). An average gauche torsion angle of 70 degrees (+/-9 degrees) was obtained. Implications for materials properties of polyesters are discussed.
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K. Schmidt-Rohr and W. Hu, Department of Polymer Science and Engineering, University of Massachusetts, Amherst, MA 01003, USA. N. Zumbulyadis, Imaging Research and Advanced Development, Eastman Kodak Company, Rochester, NY 14650-2132, USA.
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