Molecular orientation in poly(vinyl chloride) studied by Raman spectroscopy and birefringence measurements

Abstract

Abstract The ratios of the intensities of Raman scattering in the CCI stretching region for eight combinations of sample orientation and directions of polarization of incident and scattered light have been measured for 15 samples of poly(vinyl chloride) (PVC) containing 0, 5, 10, 15 or 20 pph dioctyl sebacate (DOS) plasticizer which had been drawn uniaxially at 22, 70, 75, 80, or 90°C to draw ratios in the range 1–4.5. The birefringences of the samples were also measured. The Raman data were analyzed to give 〈 P 2 (cosθ)〉 cryst and 〈 P 4 (cosθ)〉 cryst , the values of the second‐ and fourth‐order Legendre polynomials in cosθ averaged over the distribution of orientations of the crystallites, where θ is the angle between the c axis of a typical crystallite and the draw direction. Comparison of 〈 P 2 (cosθ)〉 cryst with the birefrigence showed that the crystallites are more highly oriented than the noncrystalline material in samples containing the higher amounts of plasticizer drawn at the higher temperatures. A value of 13.0 × 10 −3 was deduced for the birefringence of fully oriented PVC. The values of 〈 P 4 (cosθ)〉 cryst for a given 〈 P 2 (cosθ)〉 cryst were found to be higher than predicted by calculations based on two simple models, the pseudoaffine rigid‐rod rotation model and the affine rubber elasticity model.