A study of molecular orientation in poly(methyl methacrylate) by means of laser-Raman spectroscopy

Measurements have been made of the polarization dependence of the intensity of the Raman scattering from uniaxially oriented samples of poly(methyl methacrylate). Lines at wavenumber shifts 486, 562, 604 and 1732 cm^?1 were studied. With the right-angle scattering geometry used, four combinations of polarization directions of incident and observed scattered light could be chosen and the angle between the draw direction and the direction of the incident laser beam could be varied. The observed intensities were found to fit equations derived in an earlier publication. Five parameters which would determine the scattered intensity for any scattering geometry and combination of polarization vectors were derived. They were shown to contain information about the distribution of orientations of the structural units of the polymer despite the fact that their values also suggest that either the nature of the structural units or the interactions between them are modified by drawing. Values of $\text{cos}{}^2\text{θ}$ and $\text{cos}{}^4\text{θ}$ deduced for the structural units, where θ is the angle between a unique axis in a typical unit and the draw direction, are in good agreement with those obtained by other authors from broadline n.m.r. measurements. For the sample with the highest birefringence, ?14.8×10^?4, the values of $\text{cos}{}^2\text{θ}$ and $\text{cos}{}^4\text{θ}$ were 0.52±0.03 and 0.43±0.04 respectively.