The dynamic yield stress for polycarbonate, polystyrene and poly(methyl methacrylate) was measured by an instrumented Charpy impact tester in a wide temperature range. The dynamic yield stress is interpreted as being proportional to a negative pressure. The temperature dependence can be described by a Williams-Landel-Ferry type of equation. The extrapolation to ambient pressure leads to the main or transition and is used to connect the dynamic yield stress to the pressure dependence of the ct dispersion zone.