Shock polarization and changes in conductivity have been observed in previous electrical investigations of the shock behaviour of crystalline materials. For this reason a differential system has been designed by LLNL to separate these effects in their investigations of the conductivity of sapphire under shock. The measurement removes voltages produced in the shock electrical field allowing determination of those induced by resistance changes. Polymers are, at present, under mechanical investigation at RMCS and experiments are reported in which the thermoplastic polymethylmethacrylate (PMMA) is shocked in the range up to 10 GPa in order to observe its electrical response. The variations in induced field and in the material conductivity are reported.