Aromatic polyimides with tertbutyl-substituted and pendent naphthalene units: synthesis and soluble, transparent properties

Microstructure and Electrical Properties of Fluorene Polyester Based Nanocomposite Dielectrics

As a new type of dielectric material, the low dielectric constant and corona resistance life of fluorene polyester (FPE) restricts the range of its applications. In order to simultaneously achieve a high dielectric constant and the long corona aging lifetime of FPE, SiO₂ nanoparticles were chosen as additive to prepare FPE-based composite films. The microstructure of the composite film was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), infrared spectroscopy (IR) and small-angle X-ray scattering (SAXS). The dielectric performances of the composites, including the dielectric constant, breakdown strength and corona resistance lifetime, were investigated. The results show that the introduced SiO₂ does not destroy the structure of the FPE molecular chain and that it increases the thickness of the filler-matrix interface. The dielectric constant of SiO₂/FPE composites increased from 3.54 to 7.30 at 1 Hz. Importantly, the corona resistance lifetime increased by about 12 times compared with the pure FPE matrix. In brief, this work shows what possibilities there might be when considering the potential applications of high-strength insulating materials.

Design and synthesis of high heat-resistant, soluble, and hydrophobic fluorinated polyimides containing pyridine and trifluoromethylthiophenyl units

In this study, a novel diamine monomer, 4-(4-trifluoromethylthiophenyl)-2,6-bis(4-aminophenyl)pyridine (FTPAP) was synthesized through two-step reaction from 4-trifluoromethylthiobenzaldehyde and 4-nitroacetophenone as raw materials, and then the structure of FTPAP was characterized by Fourier transform infrared (FTIR) spectroscopy, nuclear magnetic resonance, and mass spectrometry. A series of fluorinated polyimides were prepared from FTPAP with five commercial dianhydrides, namely, pyromellitic dianhydride, biphenyl tetracarboxylic dianhydride, oxydiphtahalic anhydride, benzophenone tetracarboxylic dianhydride, and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride. The structure and performance of the fluorinated polymers were fully characterized by FTIR, differential scanning calorimetry, thermogravimetric analysis, and wide-angle X-ray diffraction (WAXD). The inherent viscosity of polymers ranged from 0.41 to 1.45 dL g−1. These polymers displayed good solubility in polar aprotic solvents, such as N, N-dimethylformamide, N, N-dimethylacetamide, dimethyl sulfoxide, and N-methyl-2-pyrrolidone, at room temperature or on heating. Furthermore, they exhibited outstanding thermal stability with glass transition temperatures beyond 305°C, and the temperature of 10% weight loss was in the range of 514–573°C with more than 56% residue at 800°C under nitrogen. Moreover, they showed high optical transparency with the cutoff wavelengths in the range of 385–457 nm and excellent hydrophobic property with contact angle in the range of 82.8–97.6°. In addition, the results of WAXD indicated that all of the polymers presented amorphous structure.

Synthesis and characterization of organosoluble, transparent, and hydrophobic fluorinated polyimides derived from 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-trifluoromethyltoluene

A novel aromatic fluorinated diamine monomer, 3,3′-diisopropyl-4,4′-diaminodiphenyl-4′′-trifluoromethyltoluene, was synthesized by coupling of 2-isopropylaniline and 4-(trifluoromethyl)benzaldehyde and its structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, elemental analysis, and mass spectrometry, and then used to prepare a series of fluorinated polyimides (FPIs) by polycondensation reaction with various commercial dianhydrides via conventional one-step method. The obtained FPIs present excellent solubility in most organic solvents and enough to cast into tough and flexible films. All the FPI films show good optical transparency and light color with the cutoff wavelengths in range of 307–362 nm and the average transmittance above 86%. These polymer films also exhibit high glass transition temperature in range of 261–331°C and thermal stability with 10% weigh loss above 463°C under nitrogen atmosphere. Furthermore, they exhibit outstanding mechanical properties with tensile strengths of 65.9–94.3 MPa, elongation at break of 11.4–13.8%, Young’s modulus of 1.6–1.9 GPa, and low dielectric constants in range of 2.75–3.10 at 1 MHz as well as prominent hydrophobicity with the contact angle in the range of 87.3–93.9°.