Molecular orientation in poly(ethylene terephthalate) by means of laser–raman spectroscopy

Abstract

Abstract The intensity of the Raman scattering from uniaxially oriented amorphous poly(ethylene terephthalate) tapes at wave number shifts of 1732, 1616, 1286, 857, and 632 cm −1 has been observed for various combinations of incident and scattered light polarization vectors with respect to the draw direction. An attempt has been made to analyze the data to provide values of 〈 P 2 (ζ)〉 and 〈 P 4 (ζ)〉, where P n (ζ) is the n th order Legendre polynomial in ζ,ζ is the cosine of the angle between the draw direction and a typtical chain axis in the polymer, and the angle brackets denote the average value over all repeat units. This attempt was successful for the 1616 and 632 cm −1 lines but less successful for the other three, although the data for the 1732 and 1286 cm −1 lines could be analyzed to provide quantities proportional, but not equal, to 〈 P 2 (ζ)〉. In the analysis and discussion two possible models were considered for the conformation of the terephthaloyl residues in the amorphous polymer but it was not possible to reject either model conclusively. The results suggest, in agreement with previous studies by other methods, that the drawing of PET at 80°C takes place essentially as the extension of a rubberlike network which is frozen on subsequent cooling to room temperature.