Measurements are presented of the compressive stress-strain behaviour of polycarbonate (PC) and polyvinylidene difluoride (PVDF) at strain rates from 10(-4) to 10(4) s(-1) at room temperature, and temperatures from -50 to + 150 degrees C at 10(3) s(-1). These results, obtained using a split Hopkinson pressure bar and Instron testing machine, are supported by dynamic mechanical analysis (DMA) measurements on the materials. Previous researchers have observed that the yield stress of these materials is bilinearly dependent on the logarithm of strain rate. The data presented here show that the bilinearity is due to the movement of low order transitions in the materials, so that they occur at temperatures above room temperature at the higher strain rates. In particular, these transitions are the 0 transition in PC, and the glass transition in PVDF. In addition, Appendix A presents measurements of a high strain rate Poisson's ratio of polycarbonate and its evolution with strain. (c) 2005 Elsevier Ltd. All rights reserved.