Preparation And Properties Of PI/SiO₂-Al₂O₃ Nanocomposite Films

Polyimide (PI) has been widely used in electrical engineering, aerospace and microelectronic industries because of their outstanding dielectricity, mechanical, and thermal properties. In recent years, a number of studies have been conducted on preparation and general performance of PI by different workers at home and abroad. In order to improve properties of PI, methods of doped inorganic oxide into PI have been widely studied. However, the compatibility between PI and inorganic oxide still needs to be improved.In this paper, (3-aminopropyl)trimethoxysilane (APTMOS) was modified by reacting with pyromellitic dianhydride(PMDA). Then, PI/SiO₂ and PI/Al₂O₃-SiO₂ composite films were prepared by sol-gel with 4,4'-oxydianiline diamine (ODA) and pyromellitic dianhydride (PMDA) as monomer, N,N-dimethyl acetamide (DMAc) as solvent, SiO₂ collosol, Al2O3 collosol and modified APTMOS as dopant. The composite films have been characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results showed that the size of inorganic particles in PI composite films was obvious decreasd by adding modified APTMOS. Properties of the composite films were measured by dielectric breakdown strength, corona-resistance time and dielectric spectra. Influence of modified APTMOS on properties of the composite films and the relations between properties and contents of the doped inorganic oxide contents were studied. The results revealed that the dielectric breakdown strength of PI/SiO₂ composite films was 326kV/mm with SiO₂ content of 20wt%, which was 1.5 time than that of pure PI films. Corona-resistance time of PI/SiO₂ composite film with SiO₂ content of 20wt% was 26.4h, which was 14 times than that of pure PI films. Dielectric breakdown of PI/Al₂O₃-SiO2 composite film with Al₂O₃ content of 10wt% was 242kV/mm. Corona-resistance time of PI/Al₂O₃-SiO₂ composite film with Al₂O₃ content of 5wt% was 3.9h. Decomposition temperature of PI/Al₂O₃-SiO₂ composite film with Al₂O₃ content of 20wt% was the maximum.