Preparation and Characterization of Polyimide/Alumina Composite Films as Improved Solid Dielectrics

Polyimide/alumina (PI/Al2O3) nanocomposite films were prepared by incorporating different nano-sized Al2O3 contents into PI which derived from pyromellitic dianhydride (PMDA) and a flexible diamine 4,4-bis(3-aminophenoxy)biphenyl (4,3-BAPOBP). The micromorphology, chemical structure, dielectric, mechanical properties and glass transition temperatures (T-g) of prepared films were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), LCR metry, electronic tensile testing and differential scanning calorimetry (DSC). SEM images show uniform distribution of Al2O3 nanoparticles in matrix. FTIR spectra indicate that Al2O3 nanoparticles are functionalized with gamma-aminopropyl triethoxysilane (gamma-APS) and the imidization was complete. XRD patterns reveal the peaks of PI/Al2O3 composite films were similar to those of Al2O3, indicating that the crystal structure of Al2O3 remains unchanged and stable after being doped into PI matrix. Meanwhile, the effects of additives on the dielectric and mechanical properties of composite films were also studied. The results show the dielectric constant and dielectric loss of hybrid materials increase with the addition of Al2O3 nanoparticles. The electrical breakdown strength and tensile strength of PI/Al2O3 can be markedly improved by the addition of appropriate amounts of Al2O3 to the PI matrix.