Preparation Of PI/SiO₂ Nanocomposite Films By A Water-soluble Polyimide Precursor And Its Structure And Properties

A water-soluble polyimide precursor,poly(amic acid)amine salt(PAD), which was from pyromellitic dianhydride(PMDA),4,4'-oxydianiline (4,4'-ODA)and N,N'-dimethylethanolamine(DMEA),was synthesized.A series of polyimide/silica(PI/SiO₂)nanocomposite films with different silica contents were successfully prepared by this precursor.PAD was synthesized from PMDA and 4,4'-ODA,and its imidization process was traced by IR and DMTA.Comparing with the imidization process of PAA,the result showed that two imidization process are similar.100nm and 50nm silica nanopaticles were synthesized by Stober method. Because of their original dispersion in water,we made PI/SiO₂ nanocomposite films from PAD and SiO₂ aqueous solution.All the films were characterized by TEM,mechanical properties,TGA and DMTA,water absorption and dielectric properties.The results indicated that with the increasing of the content of silica,the modulus presented linear enhancement;as to the thermal properties,the thermal stability enhanced,the dielectric constants changed a little and the water absorption decreased.