Rayleigh-Brillouin light-scattering studies on atactic polystrene

Abstract

Rayleigh‐Brillouin light‐scattering studies have been carried out on atactic polystyrene thermally polmerized under vacuum from scrupulously clean styrene monomer. The ratio of the central Rayleigh intensity I_R to the total Brillouin intensity 2I_B appears to be a function of T⁻¹. Depolarization intensities have also been measured and, in particular, we find that ρ_H=1 for this polymeric glass. Theoretical predictions for I_R/2I_B are discussed in light of these results. We conclude that local isotropy due to strain fields frozen into glass is negligible or in low concentration. Annealing studies confirm this result which is in disagreement with our previous results for poly(butyl) methacrylate. In addition, we find that the change in slope of the Brillouin frequency shift ω versus absolute temperature T defines a T_g 10–12 K below that measured by DSC and that ω (glass) increases with decreasing molecular weight, in agreement with previous results. A study of the relaxation of a few degrees below T_g for periods of a month and more does not shift T_g (from ω vs T) to lower temperatures for these high‐molecular‐weight polystyrene samples.