To improve the optical transparency and organosolubility of aromatic polyimides derived from 4,4 0 -oxydianiline (4,4 0 -ODA), two new aromatic diamines, 2,2 0 -diiodo-4,4 0 -oxydianiline (DI-ODA) and 2,2 0 -bis0 -oxydianiline (BTFP-ODA) were synthesized by using 4,4 0 -ODA as a starting material. Novel polyimides were prepared from these two diamines with various commercially available aromatic dianhydrides via a one-step high-temperature polycondensation procedure. Most of these polyimides showed enhanced solubility in common organic solvents compared with those corresponding polyimides derived from 4,4 0 -ODA. Especially, polyimide derived from BTFP-ODA and rigid pyromellitic dianhydride (PMDA) was also soluble in DMF, DMAc, DMSO, NMP, and m-cresol at room temperature. These polyimides had inherent viscosities from 0.41 to 1.26 dLg À1 in NMP or m-cresol at 30 C. Transparent, flexible, and tough films can be obtained by casting from their DMAc or m-cresol solutions. These films had the UV onset wavelengths in the range of 347-391 nm and the wavelengths at 80% transmission of 445-544 nm, indicating high optical transparency. They also exhibited good thermal stability with glass transition temperatures in the range of 260-327 C. The decomposition temperatures of these polyimides at 5% weight loss under nitrogen were 429-609 C. Because of the weak carbon-iodine bond, polyimides derived from DI-ODA decomposed at lower temperatures than polyimides derived from BTFP-ODA. The effects of the substituents at the 2 and 2 0 positions of 4,4 0 -ODA on the properties of polyimides are also discussed. High optical transparency and good solubility combined with high thermal stability make these polyimides potential candidates for soft electronics applications.
The binder‐free composite films of reduced graphene oxide (rGO) and activated carbon derived from cotton (aCFC) have been fabricated and used as electrodes for electrochemical capacitors (ECs) to avoid the decrease of capacitive performance in traditional process caused by the additional binder. The optimal aCFC is prepared at 850 °C when the mass ratio of carbon and potassium hydroxide is 1 to 4. The optimal composite film prepared from the mass ratio of aCFC/GO=2/1 exhibits porous structure, and has a specific surface area of 849.6 m2•g−1 and a total pore volume of 0.61 mL•g−1. Based on the two‐electrode system testing in 6.0 mol/L KOH electrolyte, the optimal composite has specific capacitance of about 202 F•g−1, 374 mF•cm−2 and 116 F•cm−3 in terms of mass, area and volume, and shows excellent rate capability and good cyclic stability (91.7% retention of the initial capacitance after 5000 cycles). Furthermore, the assembled solid‐state ECs by using KOH/polyvinyl alcohol as electrolyte show good mechanical stability and capacitive performances after repeated bending cycles. It is proved that this method is effective to fabricate binder‐free electrodes for ECs and will open up a novel route for the reuse of waste cotton.
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