Transparent polyimides derived from phenyl group substituted 2,2′-bis (trifluoromethyl)benzidines with low dielectric constant at high frequencies

With the rapid advancement of 5G communication, polyimides, currently employed as an insulating interlayer material in commercial applications, can no longer fulfill the low dielectric constant and low dielectric loss requirements imposed by high-frequency signals. To solve this problem, increasing the free volume between molecular chains is a practical and effective way to achieve the low dielectric constant of polyimides. In this work, two novel diamines with different bulky phenyl groups at ortho position of the amino group of 2,2 '-bis (trifluoromethyl)benzidine (TFDB) were designed and synthesized successfully through electrophilic substitution and Suzuki-Miyaura coupling. Then a series of polyimides were prepared with these diamines and 4,4 '-(hexafluoroisopropylidene)diphthalic anhydride (6FDA). All polyimides exhibited glass transition temperatures of 318-351 degrees C, excellent optical transmittances of 82.5-85.9 % at 400 nm, and low dielectric constants of 2.30-2.65 at 11 GHz. And they showed good solubility and hydrophobicity. The PI-5 exhibited the best dielectric properties with a dielectric constant of 2.30 and a dielectric loss of 0.0037 at 11 GHz, demonstrating promising application prospects in high-frequency communication.