High‐Performance N‐Substituted Benzimidazole‐Based Polyimide Films With Low Dielectric Constant and Dielectric Loss

ABSTRACT The advancement of microelectronics, sophisticated packaging and flexible electronics demands dielectric materials with high thermal stability, low dielectric constant ( D k ) and low dielectric loss ( D f ). In this work, a novel twisted and asymmetric N‐substituted benzimidazole‐based diamine monomer, 2‐aminobenzyl‐1‐aminobenzylmethyl‐1 H ‐1, 3‐benzimidazole (BIMA) was synthesized via a facile and efficient route. A series of polyimides coded PBI‐ x were prepared by copolymerizing BIMA with commercial 4, 4′‐oxydianiline (ODA) and 4, 4′‐(hexafluoroisopropylidene) diphthalic anhydride (6FDA) at various diamine molar ratios (BIMA: ODA = 0: 100 to 25: 75). The incorporation of the twisted rigid BIMA with large rotation energy barrier effectively reduces molecular chain packing density and increases the fractional free volume, which simultaneously improves both the solubility and dielectric properties of the PBI‐ x . Even at a small loading, the benzimidazole‐imide segments play a significant role in improving dielectric properties ( D k as low as 2.64 and D f as low as 0.0089 at 1 MHz), maintaining good thermal stability ( T g = 287°C–321°C) and good optical transparency (transmittance at 500 nm ranging from 84.7% to 90.3%). These modified copolyimides PBI‐ x demonstrate outstanding overall performance and show promising potential for applications in high‐frequency communication, high‐speed integrated circuits, flexible displays and transparent electronics devices.