Effects of chain orientation of Raman and Brillouin scattering spectra of hydrostatically extruded polypropylene

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Abstract
Raman and Brillouin scattering techniques have been used to study the effect of chain orientation in uniaxially extruded isotactic polypropylene. The orientation parameters 〈P2〉 and 〈P4〉 are obtained by measuring several Raman scattering intensities associated with the CH2 rocking mode at 841 cm−1. Both 〈P2〉 and 〈P4〉 parameters represent the average of the local orientational distribution of the polypropylene backbone. The Raman scattering result for 〈P2〉 is found in good agreement with the previous study using another vibrational band. The high-frequency elastic constants C11, C33, C44, and C13 of extruded isotactic polypropylene are determined by Brillouin scattering. The elastic constants of deformed polymers have been related to the orientation parameters determined by Brillouin scattering. The result obtained for 〈P2〉 at high extension using Brillouin scattering is found to be smaller than that of Raman. The result suggests that the pair orientation correlation between segments is important in affecting the hypersonic velocity.