Characterization of uniaxially drawn poly(ethylene terephthalate) by CP/MAS 13C NMR and X-ray diffraction

The phase structure of uniaxially drawn poly(ethylene terephthalate) (PET) has been studied by CP/MAS C-13 NMR spectroscopy and X-ray diffraction. CP/MAS C-13 NMR spectra show that the chemical shift values of the carbonyl and ethyleneglycol carbons of the non-annealed PET shift to high field as the draw ratio increases, but that the chemical shift values of the crystalline-peak for the heal-set PET shift to high field as the draw ratio decreases. Experimental results suggest that the process of crystallization is affected by the semi-ordered structure in the amorphous phase at the primary stage of the strain. These results show that there are some structural differences between PET crystals of low-stretched films and high-stretched ones before annealing. (C) 1998 Elsevier Science B.V.