Construction of all-organic low dielectric polyimide hybrids via synergistic effect between covalent organic framework and cross-linking structure

Polyimide (PI) is a promising electronic packaging material, but it remains challenging to obtain an all-organic PI hybrid film with decreased dielectric constant and loss without modifying the monomer. Herein, a series of all-organic PI hybrid films were successfully prepared by introducing the covalent organic framework (COF), which could induce the formation of the cross-linking structure in the PI matrix. Due to the synergistic effects of the COF fillers and the cross-linking structure, the PI/COF hybrid film containing 2 ​wt% COF exhibited the lowest dielectric constant of 2.72 and the lowest dielectric loss (tan $\delta$) of 0.0077 ​at 1 ​MHz. It is attributed to the intrinsic low dielectric constant of COF and a large number of mesopores within the PI. Besides, the cross-linking network of PI prevents the molecular chains from stacking and improves the fraction of free volume (FFV). The molecular dynamics simulation results are well consistent with the dielectric properties data. Furthermore, the PI/COF hybrid film with 5 ​wt% COF showed a significant enhancement in breakdown strength, which increased to 412.8 ​kV/mm as compared with pure PI. In addition, the PI/COF hybrid film achieve to reduce the dielectric constant and thermal expansion coefficient (CTE). It also exhibited excellent thermal, hydrophobicity, and mechanical performance. The all-organic PI/COF hybrid films have great commercial potential as next-generation electronic packaging materials.