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AbstractDuring the fabrication of black polyimide composite films, it is common to introduce carbon black (CB) into this composite system. The introduction of CB significantly decreases the resistivity of the films and consequently has a great effect on the inherent insulation property of polyimide. Here, the exploration of the conductive mechanism of CB/polyimide composite films is aimed to explain the change on resistivity fundamentally. In this study, two kinds of representative CBs were chosen to prepare CB/polyimide composite films. The rudiment of the conductive mechanism was built up based on the resistivity curves, and scanning electron microscopy (SEM), tensile, thermal gravimetric analysis, Fourier transform infrared (FT-IR) spectroscopy, UV, Raman and X-ray diffraction (XRD) were conducted to confirm it. The experimental results further verified the mechanism and gave us a chance to propose an integrated conductive mechanism including three sections (tunneling effect mechanism, conductive network mechanism and doping mechanism) for CB/polyimide composite films. As the conductive mechanism has been understood, it paves the way for optimization of the fabrication of conductive black polyimide films and insulating black polyimide films, even other colorful polyimide composite films.

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A fluorinated diamine monomer containing flexible ether linkage and bulky trifluoromethyl substituents, namely, bis(4‐amino‐2‐trifluoromethylphenyl) ether (a), is employed to react with nonfluorinated 1,4‐bis(3,4‐dicarboxyphenoxy) benzene dianhydride (3) and CF3‐free 2,2‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl] propane dianhydride (4), respectively, to prepare 2 novel soluble and optically transparent semi‐fluorinated poly (ether imide)s (PEIs; 3a and 4a). Compared with the corresponding PEIs based on nonfluorinated 4,4′‐diaminodiphenyl ether (b) and CF3‐free pyromellitic dianhydride (5), the novel semifluorinated PEIs 3a and 4a not only display better solubility in some organic solvents and higher optical transparency with cutoff absorption wavelength (λ0) below 370 nm but also maintain outstanding mechanical properties and thermal stability. 3a and 4a have tensile strength beyond 80 MPa and possess glass‐transition temperatures (Tg) beyond 210°C, coupled with the temperatures of 5% weight loss (T5%) exceeding 500°C. It is also found that 3a and 4a exhibit contact angles against water beyond 110° and water absorptions below 0.8% together with dielectric constants less than 3.2.

Two kinds of thermoplastic polyimides (PIs) were synthesized via a two-step method with 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP), 4,4′-oxydianiline (ODA) diamine, and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), and their thermal degradation kinetics was studied by thermogravimetric analysis at different heating rates under nitrogen. Derivative thermogravimetric analysis curves indicated a simple, single-stage degradation process in PI BTDA-BAPP and a two-stage degradation process in PI BTDA-ODA-BAPP. The activation energies ( Eas) of the thermal degradation reaction were determined by the Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose methods without a knowledge of the kinetic reaction mechanism. By comparing the values of Ea and weight loss temperatures, it was demonstrated that the thermal stability of PI BTDA-ODA-BAPP was superior to that of PI BTDA-BAPP.