A novel diamine, 1H,1′H‐(2,2′‐bibenzimidazole)‐5,5′‐diamine (DPABZ), containing bisbenzimidazole unit was successfully synthesized, and used to prepare a series of copolyimides BPDA:(ODAm/DPABZn) by polycondensation with 4,4‐diaminodiphenyl ether (ODA) and 4,4‐biphthalic anhydride (BPDA). For comparison, a series of copolyimides BPDA:(ODAm/PABZn) based on another benzimidazole diamine 5‐amino‐2‐(4‐aminobenzene)‐benzimidazole (PABZ) was also prepared. As a result, with the increase of PABZ or DPABZ content, the heat resistance (Tg and Td) and mechanical properties (σ and E) of the resulting polyimide (PI) films increased, while the coefficient of thermal expansion (CTE) decreased. Overall, the DPABZ‐based PIs showed higher Tg values and much lower CTE values than PABZ. As the content of PABZ increased, the water absorption of PABZ‐based PIs increased obviously, but no significant change in DPABZ‐based PIs. The intramolecular hydrogen bonding in DPABZ‐based PIs caused by the diamine DPABZ was believed to be the reason for the aforementioned differences. The BPDA: DPABZ film with low‐water adsorption of 2.1%, high‐Tg value of 436°C and low‐CTE value of 5.4 ppm/°C could be a promising new generation of flexible display substrates.
A novel modified PBII was achieved. The incorporation of N-phenyl group not only improved the properties but also healed the problem of high H2O-absorption for traditional PBIIs.
To introduce intramolecular hydrogen bonds in the polyimides (PIs), 5(6)‐amino‐2‐(5‐aminopyridin‐2‐yl)‐benzimidazole (PyPABZ) were designed and synthesized. The intramolecular interaction was indicated by Fourier transform infrared when different copolyimides were prepared with 4,4′‐oxydianiline and PyPABZ. These modified poly(benzimidazole imide)s eliminate the problem of high water absorption for benzimidazole (BI)‐containing PIs in the materials applications. Moreover, the high packing coefficient and rigidity of these copolyimides caused by the strong intramolecular interaction from the H‐bonding and the resulting PIs exhibited outstanding thermal properties such as high glass‐transition temperature (Tg) and low coefficient of thermal expansion.
Polyimides (PI's) with low‐dielectric constant and excellent organic solubility have broad application prospects in the electronic field. Herein, this study designed a series of novel, low dielectric, organic soluble PI films by creatively introducing fluorene and pyridine ring into diamine monomers. Because of the noncoplanar structure of fluorenyl and the polarization of pyridine ring, PI films achieved a low‐dielectric constant (2.22–3.09 at 10 MHz) and excellent organic solubility. Even in some organic solvents with low‐boiling points, these PI films still exhibited outstanding solubility. In addition, all the films possessed high‐tensile strength (≈120 MPa) and excellent optical transparency (>70%, 450 nm). It was worth noting that the glass transition temperature of films was all above 280°C and 5% weight loss temperature (T5%) was at 486–553°C. In general, the novel high‐performance low‐dielectric PI films are expected to be used in the field of microelectronics.
Three novel diamines, incorporating benzimidazole and amide moieties, namely 4‐amino‐N‐(5‐amino‐benzimidazol‐2‐yl)‐benzamide (6a), 4‐amino‐N‐(5‐amino‐1‐ methyl‐benzimidazol‐2‐yl)‐benzamide (6b), and 4‐amino‐N‐(5‐amino‐1‐phenyl ‐benzimidazol‐2‐yl)‐benzamide (6c), were designed and synthesized. A series of poly(benzimidazole‐amide‐imide) (PBIAI) films were prepared from the resulting diamines and 4,4‐biphthalic dianhydride (BPDA). These flexible polyimides (PIs) showed high glass transition temperatures (Tg = 353–379°C), low coefficients of thermal expansion (CTE = 3.7–12.3 ppm K−1) and good mechanical properties (σ = 152–207 MPa and E = 4.5–7.7 GPa), promising candidates for applications in flexible‐display substrates. Furthermore, the data guided a feasible method to enhance Tg and reduce CTE by introducing benzimidazole and amide units into PI main chains, and the effect of different N‐substituents on performance was revealed.
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