Enhancement of Dielectric Constant of Aromatic Polyimides by Introducing 4,5-Diazafluorene Structure

• Main Authors: Tan, Ben, Hu, Shichun, Yang, Liuqing, Zhu, Benqin, Jiang, Liuhao, Feng, Yang, Yue, Yishi, Sun, Zezhong
• Format: Conference Proceeding
• Language: English
• Subjects: Broadband communication; Dielectric constant; Energy storage; Fluorine; High frequency; High-k dielectric materials; Polarization; polyimide; Polyimides; Temperature measurement; Thermal stability
• ISSN: 2644-271X
• DOI: 10.23919/CMD62064.2024.10766330

With the development of energy storage technology, the requirement for material with high dielectric constant (\boldsymbol{\varepsilon}) is increased. Compared with traditional high k material, aromatic polyimide (PI) not only possesses much higher thermal stability, but also has the advantages of easy and mild synthesis conditions. Moreover, the diversity of its molecular structure provides us with the possibility to precisely control its dielectric properties in different application scenarios. In this paper, three polyimides containing 4,5-diazafluorene structure (PI-I, PI-II and PI-III) were synthesized from different diamine and dianhydride monomers. For PI-I and PI-II, 4,5-diazafluorene structure was introduced into the dianhydride while PI-III in diamine. Effect of trifluoromethyl and pyridine on 4,5-diazafluorene based polyimide were also studied. Broadband dielectric spectra were measured by using Concept 80 Novocontrol broadband dielectric spectrometer at different temperatures from 30°C to 190°C. It is found that the dielectric constant of polyimide significantly enhanced by introducing 4,5 -diazafluorene structure compared with PI of Kapton structure. PI-II shows the highest dielectric constant in three PIs, while PI-III shows the lowest value. Meanwhile, for 4,5-diazafluorene in diamine, the (\boldsymbol{\alpha}) polarization process caused by the motion of molecular chains move to lower frequency compared with the those of 4,5-diazafluorene located in dianhydride. Furthermore, the introduction of trifluoromethyl and pyridine can also make different effects on the polarization process of the polyimide, thereby affecting its dielectric constant. As a conclusion, 4,5-diazafluorene can be used to enhance the dielectric constant of polyimide and can be further modified by introducing polar groups. The method in this paper provides a new method to design and synthesize high \boldsymbol{\varepsilon} polyimide with mild synthesis condition and high \boldsymbol{\varepsilon} simultaneously, which is important for practical application of high \boldsymbol{\varepsilon} material.