Influences of Large Pendent Groups to Chain Conformation and Electrical Energy Loss at High Frequency of Polyimides through All-Atomic Molecular Simulation

Polyimide is a potential material for high-performance printed circuit board materials because of its excellent thermal and mechanical properties and chemical stabilities. Flexible printed circuit boards must have a low static dielectric constant and loss (low-Dk/Df) to reduce signal loss in high-speed communication devices. Engineering the molecular structure of polyimides with large pendant groups is a strategy to reduce their dielectric constant. However, there is no systematic study on how the large pendant groups influence electrical energy loss. We integrated all-atomic molecular dynamics and semiempirical quantum mechanical calculations to examine the influence of pendant groups on polymer chain conformation. In addition, we proposed an efficient way to determine electrical energy loss at high frequencies. We analyzed the radius of gyration, relative shape anisotropy, dipole moment, and degree of polarization of selected PI polymer chains, TPAHF, TmBPHF, TpBPHF, MPDA, TriPMPDA, m-PDA, and m-TFPDA. The simulation results show that anisotropy perpendicular to the chain direction and chain rigidity of polyimides with large pendant groups correlate more to electrical energy loss than their dipole moment magnitudes. Polyimides with anisotropic pendant groups and significant chain rigidity reduce electrical energy loss. Polyimides with soft and isotropic polymer chains easily have local structural changes by external electric fields, leading to electrical energy loss.