The influence of diamine structure on low dielectric constant and comprehensive properties of fluorinated polyimide films

Three kinds of polyimide (PI) films with low dielectric constant and excellent comprehensive properties were prepared by polycondensation reaction employing 6FDA as the dianhydride monomer and 6FODA, TFMB and 6FDAM as the diamine monomers, respectively. The effects of diamine moieties on the low dielectric constant and comprehensive properties were investigated by experiments and theoretical simulations. All three PI films show excellent high temperature resistance. For instance, the 5 % weight loss temperature ranges from 495 to 511 °C, and the T g from 305.5 to 347.2 °C. 6FDA/6FODA exhibits a higher dielectric constant ( k ) compared with the other two PIs because of low free volume fraction and low rotating energy barrier of torsion angle for 6FODA moieties. 6FDA/TFMB exhibits ultra-low k (1.84 at 10 4  Hz) being benefit from its high free volume fraction caused by the strong rigidity of molecular chain. Despite having the highest free volume fraction among the three PIs, 6FDA/6FDAM exhibits a slightly higher dielectric constant than 6FDA/TMFB due to the fact that the torsion angle for 6FDAM moieties has low rotating energy barrier, which is beneficial for improving the molecular polarizability. Meanwhile, all the PI films show excellent transparency in the visible light range as well as excellent mechanical properties. The results indicate that the microstructure of PI can be effectively adjusted, thus achieving an ultra-low k and excellent comprehensive properties by rationally designed diamine moiety.