Brillouin scattering study of polymer dynamics

The elastic properties of intermediate polymer molecules and gigahertz dynamics in a liquid-glass transition have been studied by the Brillouin scattering method. To clarify the interaction of epoxy ring end groups and the effect on polymer chain length, we investigated poly(propylene glycol)diglycidyl ether (average molecular weight 380 and 640 g/mol). The new technique of Brillouin scattering, angular dispersion-type Fabry-Perot interferometer with a highly sensitive charge-coupled device enables a rapid measurement in cooling process. A high spectral resolution and the contrast comparable to the conventional scanning-type are achieved by a high reflectivity solid etalon. The relaxation time derived from the Brillouin scattering measurement was faster than those of dielectric results, and its temperature dependence well obeys the Arrhenius law. The activation energy and the attempt frequency show similar tendency, suggesting that it originates from the local segmental motions of the backbone structure, which is independent of the chain length in polymers. Since the derived relaxation time is an averaged quantity, there is no information of relaxation time distribution. The results explain that the distribution of relaxation times narrows when the chains become shorter, and the distribution is reflected to the broadness of the Brillouin width versus temperature curve.