A pulsed NMR study of the effects of initial morphology on the structure of extrusion‐drawn poly(ethylene terephthalate)

Proton spin–spin relaxation times and the Weibull coefficient have been measured as functions of temperature for poly(ethylene terephthalate) (PET) drawn at 50°C in both the amorphous and the semicrystalline (50%) states. Two relaxation times T 2 a (long) and T 2 c (short) are observed for all samples. They are ascribed, respectively, to the relaxation of the amorphous and of the crystalline components including highly strained noncrystalline segments. Effects of initial morphology are found for chain mobility in the noncrystalline regions and for the crystal perfection, evaluated from T 2 a and the Weibull coefficient μ c of the T 2 c ‐component, respectively. For all draw ratios, T 2 a for extrudates prepared from the semicrystalline polymer (C‐50) is short compared to that for preparations from the amorphous (A‐50) polymer. In the A‐50 samples, the perfection of stress‐induced crystals increase with increasing draw ratio. In the C‐50 samples, the crystal orientation increases, whereas the perfection decreases with increasing draw ratio. To improve the crystal perfection, annealing at higher temperature or longer time is required for C‐50 as compared with A‐50. The value of μ c correlates well with the change in crystal perfection during deformation and annealing.