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°C) are investigated for its high temperature use as an insulating material in the range above 250°C in order to extend the limit of conventional PAI (c-PAI, T_g=277°C). Four dielectric processes are identified between 50°C and 400°C. Among them, the electrical conduction (σ-conduction) is clearly reduced particularly in the range from 250°C to 320°C, i.e. T_g(c-PAI)≤T≤ T_g(hTg-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°C), the σ-conduction of hT_g- PAI has an activation energy of 2.3 eV (~221.9 kJ mol-1).