LOW-FREQUENCY RAMAN-SPECTROSCOPY OF PLASTICALLY DEFORMED POLY(METHYL METHACRYLATE)

The low-frequency Raman scattering (2-200 cm(-1) range) of poly(methyl methacrylate) (PMMA) specimens plastically deformed in pure shear is compared to that of non-deformed specimens. The main experimental feat ure is an excess of Raman scattering in the 30-50 cm(-1) spectral rang e induced by plastic deformation. This excess appears to be strongly a nisotropic and is maximum when the light polarization is orthogonal to the principal tensile strain component, i.e. to the chain orientation direction. The effect is still present, but with a weaker anisotropy, after mechanical cycling when the macroscopic deformation is brought back to zero by application of an opposite stress. These observations are interpreted in terms of the non-continuous nature of the disordere d network on the nanometric scale. The orientation of macromolecular s trands induced by plastic deformation is shown to be higher in the les s cohesive spaces.