Effect of hydrostatic pressure on the viscoelastic response of polyurea

Dielectric spectroscopy is used to measure the local segmental relaxation times for the soft segments of a polyurea as a function of temperature and pressure, In combination with the equation of state determined for the material, we show that the relaxation times are uniquely defined by the product of temperature times specific volume, with the latter raised to the power of 2.35 +/- 0.10. This superpositioning of the relaxation times enables both the local segmental and the global chain dynamics to be calculated for any combination of temperature and pressure, using only measurements at ambient pressure. Since this polyurea finds applications as a coating to mitigate the damage from impact loading, its response to high frequencies and elevated hydrostatic pressure is of some import. (C) 2007 Elsevier Ltd. All rights reserved.