Polyimide/mica (PI/mica) hybrid films were prepared from pyromellitic dianhydride/4,4-bis(3aminophenoxy)biphenyl (PMDA/4,3-BAPOBP) and mica in a solution of N,N-dimethylacetamide. The structure-property relationships of the composites were studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, ultraviolet-visible spectroscopy and differential scanning calorimetry. FTIR indicated successful preparation of PI/mica hybrid films. XRD and SEM results indicated that the mica was well dispersed in the PI matrix. The dependence of morphology, glass transition temperatures (T g ), dielectric properties and mechanical properties at room temperature of the hybrid films on the content of mica was discussed. It was observed that T g , the breakdown strength and tensile strength of the hybrid films, could be simultaneously increased when the mica content was lower than 8 wt-%. Meanwhile, the dielectric constant and dielectric loss of PI/mica hybrid films increased with the increase in the mica content.
To improve the properties of polyimide (PI), different mass fractions of alumina (Al 2 O 3 ) nanoparticles, unmodified or modified by KH550, were incorporated into PI matrix to form PI/ Al 2 O 3 hybrid films by in situ polymerisation. The effects of Al 2 O 3 additives on the structure, dielectric and mechanical properties of the films were studied. Fourier transform infrared spectroscopy confirmed the successful preparation of PI/Al 2 O 3 hybrid films, and the microstructures of the samples showed a more uniform dispersion of the modified Al 2 O 3 nanoparticles than the unmodified ones in the matrix. The dielectric constant of the films increased with increasing filler content, and the maximum electrical breakdown strength of 311 MV m −1 was obtained with a filler content of 8.0 wt-% modified Al 2 O 3 in the matrix. Both unmodified and modified Al 2 O 3 -reinforced PI hybrids demonstrated improved mechanical properties compared with the PI matrix. Moreover, the properties of films with Al 2 O 3 modified by KH550 were better.
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