A series of monodisperse polybutadienes has been used to perform mechanical relaxation measurements from the flow regime to the glassy state. Results on loss shear moduli have been analyzed within the framework of a coupling model. It has been found to represent well the frequency dependence in the glassy and terminal zones using a segmental motion coupling parameter beta(alpha) and an entanglement coupling parameter beta(eta). Moreover, our results on apparent shift factors resulting from time-temperature superposition are consistent with the lack of thermorheological simplicity predicted by the coupling theory due to the difference between beta(alpha) and beta(eta).