Complementary functionality of SiO2 and TiO2 in polyimide/silica-titania ternary hybrid nanocomposites

A polyimide ( PI) composite containing SiO2 and TiO2 hybridized nanoparticles was prepared by the sol-gel process. Polyamic acid (PAA) solution, the precursor of PI, was synthesized from 2,2'-bis-(3,4-dicarboxyphenyl) hexofluoropropane dianhydride and bis [4-(3-aminophenoxy) phenyl sulfone in N-methyl-2-pyrrolidone. The SiO2-TiO2 hybrid nanoparticles were prepared by the sol-gel process in a PAA solution into which tetraethoxysilane, titanium (IV) tetrabutoxide and acetylacetone were mixed for subsequent hydrolysis and condensation reactions. After spin coating of this solution onto a glass substrate, the stepwise imidization to PI and the simultaneous gelation of the SiO2-TiO2 hybrid oxides were achieved at 100-300 degrees C. The complementing effects of reduced particle size and enhanced thermal stability of SiO2 and TiO2 on the resulting nanocomposite were observed. The former effect was contributed by TiO2 and the latter by SiO2. Uniform dispersion of 5- to 10-nm-diameter SiO2-TiO2 nanoparticles was obtained in the PI matrix. A 5-mu m-thick film obtained from this procedure exhibited excellent optical transparency (91%, 500 nm) at 15 wt% SiO2 for a TiO2 content < 5 wt%. Polymer Journal (2011) 43, 249-257; doi: 10.1038/pj.2010.117; published online 19 January 2011