Raman microprobe spectra of spin-oriented and drawn filaments of poly(ethylene terephthalate)

Polarized Raman spectra of single filaments of spin-oriented and drawn fibres of poly(ethylene terephthalate) were recorded. Various Raman bands and their intensities correlated with (1) conformation of the glycol linkage, (2) orientation of the chains, and (3) crystallinity. Because the degrees of crystallinity and orientation were known from X-ray diffraction, density and optical birefringence, it became possible to identify features of the Raman spectra which correlated with each of the effects noted above. The degree of orientation, as a function of take-up speed or draw ratio, was correlated with the intensity ratios of the various polarization components. The appearance and increases in intensity of bands due to trans glycol conformations and the disappearance of the gauche bands with increasing orientation could be followed readily. It appears that many of the Raman bands earlier assigned to crystallinity in PET actually represent the trans conformation of the glycol group as is also observed in i.r. spectra. This conclusion is based on the observation that in spinoriented amorphous materials the trans conformation bands increase in intensity with increasing birefringence. Also an amorphous highly oriented fibre shows these same transconformation bands with high intensity. On the other hand, the width of the carbonyl band, which is the classical indicator of the amorphous or crystalline character of PET, confirmed the amorphous nature of this sample. In conclusion, by monitoring appropriate features of the Raman spectra of spin-oriented and drawn fibres, we have been able to confirm that orientation can occur independently of crystallization in PET.