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To improve the thermodynamic and mechanical properties of asymmetric polyimide (PI), a method to enhance the linearity of PI by using a structural reorganization approach was designed. First, two novel diamines containing benzimidazole and benzoxazole groups, namely PADBZ and PDBOA, were constructed and synthesized. Thereafter, two new kinds of PI films (PADBZ‐PMDA and PDBOA‐PMDA) were prepared and polymerized with 1,2,4,5‐benzenetetracarboxylic anhydride (PMDA). Based on structural reorganization, PADBZ‐PMDA and PDBOA‐PMDA had repeating units of the same chemical composition and different linearity with PABZ‐BPDA and BOA‐BPDA, respectively. Comparing PADBZ‐PMDA and PABZ‐BPDA, due to the transfer in the position of benzene, PADBZ‐PMDA with high linearity showed the improved heat resistance (Tg up to 448°C), dimensional stability (CTE down to 2.3 ppm/K) and mechanical properties. PDBOA‐PMDA and BOA‐BPDA had the same situation. This study provided a unique solution to enhance the performances of PI by increasing the linearity using a structural reorganization approach. [ABSTRACT FROM AUTHOR]

To synthesize colorless superheat‐resistant polyimide films, one of the valid approaches is the incorporation of the asymmetric and warped structures in the main chain. Applying this approach on 5(6)‐amino‐2‐(4‐aminobenzene)benzimidazole (PABZ) and changing its linearity, 6, 5′‐diamine‐2′‐methyl‐1‐methyl‐2‐phenylbenzimidazole (5a) and 6, 3′‐diamine‐2′‐methyl‐1‐methyl‐2‐phenylbenzimidazole (5b) were devised and synthesized successfully, then polymerized with 1,2,4,5‐cyclohexanetetracarboxylic dianhydride (HPMDA). The prepared poly(benzimidazole imide)s (PBIIs) with the rigid main chain and loose packing had the excellent heat‐resistant level (Tg > 400°C) and optical properties (T400 > 80%). Besides, the alterations resulting from various linearities were discussed comprehensively. This research is beneficial to the application of optical field, providing a promising candidate of heat‐resistant colorless materials. [ABSTRACT FROM AUTHOR]

Colorless polyimides (CPIs) with superheat resistance and low coefficient of thermal expansion (CTE) are required urgently to employ as plastic substrates in flexible‐display devices. To attain the target properties, 2‐(2‐methyl‐4‐(4‐aminobenzamido)phenyl)‐5‐(4‐aminobenzamido)‐N‐phenylbenzimidazol (AB‐MPBZ) that contains biamide was synthesized, and its homo‐ and co‐polyimides were prepared with 1,2,4,5‐cyclohexanetetracarboxylic dianhydride (HPMDA) and cyclobutane‐1,2,3,4‐tetracarboxylic dianhydride (CBDA). The crank‐shaft‐like amide groups effectively increases the linearity and stiffness of polymer segments, providing CPI films with low CTE. On the basis, the CBDA based poly(benzimidazole imide) (PBII) series with dense interchain packing exhibits further reduced CTE down to 22 ppm K−1 and increased glass‐transition temperature (Tg) up to 404 °C. Such good thermal properties indicate that the resultant copolyimides have potential applications as colorless flexible substrates. These provide a feasible approach to balance thermal and optical performance of polyimides. [ABSTRACT FROM AUTHOR]

Polyimides (PIs) with super heat‐resistance and ultralow coefficient of thermal expansion (CTE) are required urgently to employ as plastic substrates in flexible‐display devices. To attain the target properties, we designed and synthesized a novel bibenzimidazole diamine characterized in having a N‐phenyl group, namely 1‐phenyl‐2,2′‐bibenzoimidazole‐5,5′‐diamine (PhDABZ), and focused on an aromatic poly(benzimidazole imide) series derived from 1,2,4,5‐benzenetetracarboxylic (PMDA). Incorporating bibenzimidazole and N‐substituent effectively increase the interchain interaction and chance for flexible film formation, which provides the PIs with high glass‐transition temperature (Tg > 480 °C) and dimensional stability (CTE < 10 ppm K−1). These data provide a feasible method to achieve higher thermal properties of PIs. [ABSTRACT FROM AUTHOR]