Novel High Glass Transition Polyamide-imide: Tg Influence on Electrical Conductivity at High Temperature

The dielectric properties of a novel high-glass transition polyamide-imide (hT(g)-PAI, T-g=333 degrees C) are investigated for its high temperature use as an insulating material in the range above 250 degrees C in order to extend the limit of conventional PAI (c-PAI, T-g=277 degrees C). Four dielectric processes are identified between 50 degrees C and 400 degrees C. Among them, the electrical conduction (sigma-conduction) is clearly reduced particularly in the range from 250 degrees C to 320 degrees C, i.e. T-g(c-PAI)<= T <= T-g(hT(g)-PAI). The main reason explaining such an enhancement is the shift of ionic conduction contribution towards higher temperatures in hT(g)-PAI compared to c-PAI. In hT(g)-PAI, the higher-T-g value allows better controlling the free volume expansion responsible of large ions motions in the bulk. In the range of potential applications (i.e. 250 to 320 degrees C), the sigma-conduction of hT(g)-PAI has an activation energy of 2.3 eV (similar to 221.9 kJ mol(-1)).