Effect of molecular orientation on the elastic constants of polypropylene

The Brillouin spectroscopic measurements of elastic properties of polypropy lene films fabricated by different processing techniques are described. We find that the elastic symmetry and the associated elastic constants are dep endent on the molecular orientation brought about by the processing conditi ons used to produce the films. We have shown that Brillouin scattering tech niques can successfully be used to track the molecular orientation induced by uniaxial stretching. We find a direct correspondence between the Brillou in measurements and optical birefringence measurements, illustrating that m olecular orientation plays a dominant role in determining the mechanical an isotropy in these materials.