Brillouin-light-scattering measurements have been performed on both bulk and thin supported polybutadiene (PB) films, in the frequency range 1–300 GHz. The results obtained on the relaxation behavior of PB have been interpreted in the framework of the mode-coupling theory and compared with neutron spin-echo data relative to the same system. For temperatures higher than the critical temperature ${\mathit{T}}_{\mathit{c}}$, a quantitative agreement of the mean relaxation time with the viscosity time scale has been found, together with the validity of a time-temperature scaling law. For temperatures approaching the glass transition, a departure of relaxation time from the viscosity time scale has been observed. This phenomenon has been attributed to a decoupling between structural and secondary relaxation processes.

• Received 14 March 1994

DOI:https://doi.org/10.1103/PhysRevB.50.605