Dielectric α- and β-Relaxations in Uncured Styrene Butadiene Rubber

The development of the dynamic glass transition in styrene-butadiene copolymers has been investigated by dielectric spectroscopy in the frequency range from 10 -2 to 10 6 Hz. Two processes were detected and attributed to the α - and β - relaxations. The α relaxation time has a non-Arrhenius temperature behavior that is highly dependent on styrene content while the β relaxation time shows an Arrhenius behavior with an activation energy that is independent of styrene-content. Furthermore, the shape of the α -relaxation is strongly influenced by the styrene content while the shape of β -relaxation is not. We interpret these results as follows. The observed β -relaxation is primarily due to local motions of butadiene monomers and therefore not affected by the presence of styrene. The α -relaxation, on the other hand, is highly sensitive to the styrene content due to its cooperative character.