BENZENE-RING ORIENTATION IN UNIAXIAL-PLANAR POLY(ETHYLENE-TEREPHTHALATE) FILMS

A study is presented of the benzene ring orientation in a series of ei ght films of poly(ethylene terephthalate) drawn at constant width unde r constant force above the glass transition temperature. For each samp le, seven orientation moment averages, P(lmm)r, for the overall benzen e ring distribution were determined from a combination of Raman and in frared spectroscopic measurements. Comparison of orientation moment av erages calculated with and without the assumption of a uniaxial Raman tensor, and with and without a refractive index correction to the Rama n intensities, leads to the conclusion that the seven P(lmm)r are give n, to a good approximation, by the simplest calculation assuming a uni axial Raman tensor and neglecting the refractive index correction. The seven P(lmm)r were used to calculate the 'most probable' distribution function and the isometric projections of this distribution have been produced. The results indicate that the C1-C4 axis shows an approxima tely uniaxial overall distribution with a slight tendency to be more o riented out of the plane of the film and that the benzene rings tend t o lie in the plane of the film. From a combination of these results wi th those of earlier X-ray measurements, the amorphous and crystalline contributions to the overall molecular orientation were obtained. The results show that the benzene ring planes are preferentially oriented towards the plane of the film only in the crystalline phase and have a n almost uniaxial distribution around the draw direction in the amorph ous phase. It has been shown that, in the amorphous phase as well as i n the crystalline phase, the benzene rings tend to lie in the plane de fined by the draw direction and the C1-C4 axis.