Molecular Orientation Distributions in the Crystalline and Amorphous Regions of Uniaxially Oriented Isotactic Polypropylene Films Determined by Polarized Raman Spectroscopy

Abstract

Molecular orientation distributions in both the crystalline and amorphous regions of uniaxially oriented isotactic polypropylene (it.PP) films were determined by polarized Raman spectroscopy. By comparing polarized Raman scattering intensities of a highly oriented film for different polarization scattering geometries, the form of Raman tensor was determined for the Raman bands of it.PP. Orientation distribution coefficients, P l00, for the Raman bands were combined with the results of wide angle x‐ray diffraction (WAXD) and birefringence measurements in order to determine their tilt angle, Ω, which is the angle between the principal axis of a Raman tensor and the molecular chain axis. The angles, Ω, were determined for the first time for Raman bands assigned to both the crystalline and amorphous regions. It was shown that the molecular orientation distributions in the crystalline regions and in the amorphous regions can be determined fully by polarized Raman spectroscopy, once the tilt angle, Ω, was obtained first for a Raman band assigned to the crystalline regions only and then for one assigned to both the crystalline and amorphous regions. The study of uniaxially oriented it.PP films with different sample draw ratios (DR) revealed that the development of high molecular orientation in the crystalline regions took place up to DR=7.5. Compared to the crystalline regions, a lower degree of molecular orientation was observed in the amorphous regions, and there was a slight increase of molecular orientation above DR=7.5. Dedicated to Professor John L. Stanford on the occasion of his 60th birthday.