Dielectric susceptibility measurements of the primary and secondary relaxation in polybutadiene

We present data on the dielectric relaxation in the random copolymer polybutadiene. There are two distinct peaks in the imaginary part of the dielectric susceptibility, one of which is attributable to an {α} relaxation and the other to a Johari-Goldstein {β} relaxation. The bifurcation of these two relaxations explains the previously reported decoupling of microscopic and macroscopic time scales in polybutadiene. We show that the spectral shape of the Johari-Goldstein relaxation is consistent with a log-normal response function.