Preparation and characterization of polyimide/Al₂O₃ hybrid films by sol-gel process

A sol-gel process has been developed to prepare polyimide (PI)/Al ₂O₃ hybrid films with different contents of Al ₂O₃ based on pyromellitic dianhydride (PMDA) and 4,4′-oxydianiline (ODA) as monomers. FESEM and TEM images indicated that Al₂O₃ particles are relatively well dispersed in the polyimide matrix after ultrasonic treatment of the sol from aluminum isopropoxide and thermal imidization of the gel film. The dimensional stability, thermal stability, mechanical properties of hybrid PI films were improved obviously by an addition of adequate Al₂O₃ content, whereas, dielectric property and the elongation at break decreased with the increase of Al₂O₃ content. Surprisingly, the corona-resistance property of hybrid film was improved greatly with increasing Al₂O₃ content within certain range as compared with pure PI film. Especially, the hybrid film with 15 wt % of Al₂O₃ content exhibited obviously enhanced corona-resistance property, which was explained by the formation of compact Al₂O₃ network in hybrid film.