Pressure dependence of the local and global dynamics of polyisoprene

We report on the pressure dependence of the local segmental and normal mode s of a type-A polymer (polyisoprene) using dielectric spectroscopy. We find that external pressure exerts a stronger influence on the dynamics of the segmental mode as compared to the longest normal mode which results in the crossing of the two modes at higher pressures. The predictions of the Rouse model are not adequate to explain the different shift factors even at elev ated temperatures. (C) 1999 American Institute of Physics. [S0021- 9606(99) 50135-9].