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 feature is an excess of Raman scattering in the 30-50 cm(-1) spectral range induced by plastic deformation. This excess appears to be strongly anisotropic 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 disordered network on the nanometric scale. The orientation of macromolecular strands induced by plastic deformation is shown to be higher in the less cohesive spaces.