Elucidation of the Chain Conformation in a Glassy Polyester, PET, by Two-Dimensional NMR

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Science  01 May 1998:
Vol. 280, Issue 5364, pp. 714-717
DOI: 10.1126/science.280.5364.714

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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–13CH213CH2–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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