Synthesis and characterization of cross-linked polyimide film using tolylene diisocyanate

Abstract

Cross-linked polyimide films were synthesized by the reaction between diisocyanate groups and hydroxyl functional groups in polyimide structure, which was confirmed by IR. During the thermal treatment of the cross-linked polyimide, the thermal labile component (CO₂) in the urethane segments was decomposed which might generate pores in the film. The presence of the pores was confirmed from the dielectric constant of the film. The dielectric constant of the films decreased with the increase of TDI loading. By comparing the properties of the films, the PI50-C1.0 exhibited optimum mechanical and good dielectric properties. The cross-linked structure was also confirmed by DMA. The PI50-C1.0 showed excellent storage and loss modulus especially in the high temperature range (above 350°C) due to the characteristic of cross-linked structure. Moreover, the results of tensile stress test showed that the PI50-C1.0 exhibited lower tensile strength than the PI50 because the presence of pore in PI50-C1.0 might influence to strength greater than the effect of cross-linked structure. Finally, the SEM cross sectional images can not be observed the different between PI50 and PI50-C1.0. This might be based on that the very small size of pores, which were generated by carbon dioxide.