Synthesis and characterization of polyimide/silica nanocomposites with coupling agent

In this study, silica particles were introduced into a polyimide (PI) matrix to enhance its thermal and mechanical properties. Monomers of 3,3',4,4'-biphenyl tetracarboxylic dianhydride (BPDA) and p-phenylenediamine (p-PDA) were employed to synthesize the poly(amic acid) (PAA). Polyimide/SiO₂ composites were obtained through a sol-gel process using tetraethoxysilane and multi-step thermal curing processes. The properties of the PI/SiO₂ composites with various kinds of coupling agents to enhance the bonding between them were also studied. TGA results indicated that silica particles were dispersed uniformly in the PI matrix at the nano-scale level, as observed in SEM images. The coefficient of thermal expansion was decreased by an increase of the silica content.