Evidence for Structure in Plastics from Light Scattering

Abstract

Measurements of the indices of refraction at 6328 Å of polymerized methyl, ethyl, and butyl methacrylate (PMMA, PEMA, PBMA) as a function of temperature show a discontinuity in the slopes at the glass–rubber transition temperature. A similar discontinuity appears in the hypersonic speeds, obtained as a function of temperature from Brillouin shift measurements and the indices of refraction. From considerations involving the annealing process as seen in the index of refraction, the enhancement of the Rayleigh scattering, the large Landau–Placzek ratio, and the pronounced Krishnan effect (unequal depolarization of the horizontal and vertical components of 90° scattered light for horizontally polarized incident light), one concludes that the polymerization process freezes into the plastic shear and compressional strains that are only partially relieved by annealing.