MOLECULAR-LEVEL CERAMIC POLYMER COMPOSITES .2.1 SYNTHESIS OF POLYMER-TRAPPED SILICA AND TITANIA NANOCLUSTERS

The concept of "site isolation" was used to synthesize SiO2 and TiO2 nanoclusters trapped in polyimide matrices. M(OEt)4 (M = Si, Ti) was added to polyamic solutions derived from 4,4'-oxydianiline and either 1,2,4,5-benzenetetracarboxylic acid dianhydride or 3,3',4,4'-benzophenonetetracarboxylic acid dianhydride. Following thermal curing, polyimide films containing a homogeneous dispersion of SiO2 or TiO2 particles were obtained. Oxide nanoclusters (size < 1-1.5 nm) were present in polyimide films containing 12% TiO2 and up to 32% SiO2. However, 1-mu-m particles were present at 42% SiO2 content. Two-micrometer particles were formed even in 12% SiO2 containing films when poly(diethoxysiloxane), rather than Si(OEt)4, was used as the oxide precursor.