Polyimide/SIO₂ Hybrid Materials Based On Sol-gel Method: Preparation And Property Studies

Polyimides?PIs?are aromatic heterocyclic polymers containing an amide group in the main chain.They are widely used in aerospace,precision machinery,nuclear power and electrical and electronic fields due to the excellent thermal stability,dielectric properties,solvent resistance and mechanical strength.However,with the development of microelectronics and other related industries,polyimides with higher heat resistance and mechanical properties have been requested.Therefore,the preparation of PI hybrid films with better performance has attracted many interests.It has been indicated in previous studies that hybrid materials prepared by introduction of silica into polyimide matrix combine the advantages of organic and inorganic compounds.Sol-gel method,one of the most important strategies to prepare the hybrid materials of well dispersed inorganic substance in polymer,has thus been utilized to modify the compatibility of PI/silica matrixes.In the process of preparing PI/silica by sol-gel method,two methods are usually adopted.One method is to create additional reactive sites in the polymer matrix in order to strengthen the phase connectivity with inorganic substance.The other is to modify the inorganic components so that they are more compatible with the polymer matrix.In this paper,a series of PI/SiO₂ hybrid materials were prepared by sol-gel method with tetraethoxysilane?TEOS?or organosilica according to the followings:?1?A series of polyimide/unmodified silica?1PI-US?and polyimide/modified silica?1PI-MS?hybrid films were prepared via sol-gel process from a mixtures of poly?amic acid?and silica precursor,whereas,the PAA was synthesized from 1,4-bis?4-aminophenoxy?benzene?RODA?and bis-?3-phthalyl anhydride?ether?ODPA?.The resultant films were characterized and compared by various techniques including FT-IR,FE-SEM,TGA,tensile testing,contact angle measurements,moisture absorption measurements and dielectric property analysis.Results demonstrated that the properties of both 1PI-US and 1PI-MS hybrid matrixes showed a strong dependence on silica content,especially thermal stability and mechanical properties were greatly improved with increasing silica.Among them,PI-MS hybrid films with superior interphase interactions were found to have much better physicochemical properties.?2?Two types of SiO₂ hybrid polyimide containing hydroxyl groups were synthesized by using TEOS and organosilica as additives.The PAA was derived from 4,4'-diamino-4''-hydroxytriphenylmethane?DHTM?,RODA and ODPA in the molar ratio of 1:1:2.Silica particles or silica network were formed in polymer matrix through a programmed heating process for imidization.The test results showed that the compatibility of SiO₂ in PI matrix was greatly improved due to the presence of hydroxyl groups.The hybrid films with organosilica as an additive had much better thermal stability and mechanical properties than those containing TEOS.?3?Under high temperature conditions,polyimide solution was synthesized from 2,2'-bis?3-amino-4-hydroxyphenyl?hexafluoropropane?APAF?,4,4'-oxydianiline?ODA?and ODPA by one step method.Fluorinated polyimide/silica hybrid films were prepared by adding TEOS and 3-glycidoxypropyltrimethoxysilane?GPTMOS?to above PI solution.The obtained test results showed that the hybrid materials had obvious improvement in thermal,mechanical and moisture absorption properties compared to those of pure PI films.