Unusual Relaxation Process in Polybutadiene: Resolving the Controversy

We report the observation of an unusual relaxation process in depolarized light scattering spectra of polybutadiene (PBD) with two different vinyl contents. The process showed up in the gigahertz frequency range with relatively mild temperature dependence and was similar to a secondary relaxation process. The most surprising observation was that the process exists even at high temperatures and does not merge with the segmental relaxation up to a temperature of 400 K (T > 2T_g). Possible mechanisms of this particular relaxation in PBD are discussed. The process is compared to the so-called E process, double-bond hopping process, and dielectric β process. We emphasize that this process differs from the dielectric β process, is unique for 1,4-PBD, and has not been observed in other polymers.