The precision regulation of the dielectric polarization and dielectric loss of polymer materials, developing intrinsic high-performance polymers with high dielectric constant, low dielectric loss and excellent temperature resistance is very challenging. In this work, a facile molecular design strategy was developed by directly introducing two ortho-position aromatic nitrile groups into the rigid polyimide backbone. Compared with similar polyimides without nitrile groups (0CN-PIs), the polarizability and dielectric constant of the designed polyimide (2CN-PIs) can be greatly increased. Meanwhile, the polarization motions of the nitrile groups can be limited at room temperature, which is beneficial to lowering the dielectric loss. Among the designed polyimides, 2CN-BTDA shows a high k value of 4.80, low dielectric loss of 1.57 × 10−3 at 1 kHz (25 °C), and breakdown strength of 219.4 kV mm−1 with high maximum discharge energy density of 1.023 J cm−3. Moreover, its Tg value is as high as 325 °C, much higher than that of most traditional dielectric polymers. The essence of designing high-k–low-loss intrinsic polymers was revealed by reconsidering the Clausius–Mossotti equation, where the total polarizability should be maximized while the chain stacking should be as tight as possible; that is, a rigid polymer backbone, small sized polar groups (like nitrile groups), and a spatial position in favor of orientation polarization are preferred. The results are helpful to promote the research progress of dielectric polarization and of great significance to the development of high-performance high-k–low-loss dielectric materials for potential applications in modern electronic information and microelectronic industry.
Jianghuai Hu,Huanxin Xie,Zhengzhu Zhu,Wenjie Yang,Wei Tan,Ke Zeng,Gang Yang
High melting points (M p ) and high curing temperatures are two key processing problems that limit the application of aromatic cyano-based (AC) resins. A Brønsted acid-base synergistic strategy based on an acid-base eutectic and mechanisms for nucleophilic addition and ionization equilibrium are proposed to reduce the M p and curing temperature of AC resins. Blends of 4,5-dicyanoimidazole (DCI, Brønsted acid) and amine-containing phthalonitriles (4‐(4 or 2 or 3)‐aminophenoxy) phthalonitrile, APNs, Brønsted bases) were selected as model acid-base systems to study the synergistic behaviors in processing. The results show that the M p and the peak exothermic temperature (T rp ) of APN-DCI blends can be reduced by more than 31 °C and 85 °C compared with their intrinsic components, respectively. DSC and XRD show that the decrease in the Mp of the blends is induced by the formation of eutectics. A positive relationship between △pKa and the curing reactivity is confirmed by theory and experimental methods. The cured products show outstanding thermal and mechanical properties compared with reported AC resins. This research provides a new convenient route for regulating the curing behavior of AC resins and will significantly promote the development of high-performance AC resins.
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