The Pivotal Role of Benzimidazole in Improving the Thermal and Dielectric Performance of Upilex-Type Polyimide

Abstract

Polyimide (PI) with ultra-high thermal resistance and stability is essential for application as a flexible substrate in electronic devices. Here, the Upilex-type polyimides, which contained flexibly “twisted” 4,4′-oxydianiline (ODA), have achieved various performance improvements via copolymerization with a diamine containing benzimidazole structure. With the rigid benzimidazole-based diamine bearing conjugated heterocyclic moieties and hydrogen bond donors fused into the PI backbone, the benzimidazole-containing PI showed outstanding thermal, mechanical, and dielectric performance. Specifically, the PI containing 50% bis-benzimidazole diamine achieved a 5% decomposition temperature at 554 °C, an excellent high glass transition temperature of 448 °C, and a coefficient of thermal expansion lowered to 16.1 ppm/K. Meanwhile, the tensile strength and modulus of the PI films containing 50% mono-benzimidazole diamine increased to 148.6 MPa and 4.1 GPa, respectively. Due to the synergistic effect of rigid benzimidazole and hinged, flexible ODA, all PI films exhibited an elongation at break above 4.3%. The electrical insulation of the PI films was also improved with a dielectric constant lowered to 1.29. In summary, with appropriate mixing of rigid and flexible moieties in the PI backbone, all the PI films showed superior thermal stability, excellent flexibility, and acceptable electrical insulation.

Structural Designs of Transparent Polyimide Films with Low Dielectric Properties and Low Water Absorption: A Review

“…But polyimides have low coefficients of thermal expansion (~20 ppm/°C) and high tensile strength, and thus, they can withstand higher temperatures (>400 °C). Further, the synthesis and fabrication of PIs are simple and cost-effective [ 20 , 21 ]. Nowadays, therefore, polyimides (PIs) are replacing LCPs because of their unique advantages.…”

“…However, they suffer from several severe Nanomaterials 2023, 13, 2090 3 of 37 problems, like the tearing problem during the manufacturing process, the bad adhesion and poor reliability of the molded plates in the early stage of injection (up to 1/3 volume), and low dielectric stability above 100 • C. But polyimides have low coefficients of thermal expansion (~20 ppm/ • C) and high tensile strength, and thus, they can withstand higher temperatures (>400 • C). Further, the synthesis and fabrication of PIs are simple and costeffective [20,21]. Nowadays, therefore, polyimides (PIs) are replacing LCPs because of their unique advantages.…”