Polyetherimide (PEI)/SiO2 composites were in situ prepared via sol-gel process in the presence of tetraethyl orthosilicate (TEOS) in a mixed solvent of N

N-Dimethylacetamide/tetrahydrofuran (DMAc/THF).Electronic microscopy was used to check dispersion quality in transmission mode and scanning mode

and the results showed that SiO2 particles could be uniformly dispersed in the composite under a certain amount (20 wt%) and the average size of the particles could be controlled within a compass of 80~300 nm.However

glomeration may occur if the concentration of SiO2 particles was beyond this range.Results of Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the glass transition temperature (Tg) and decomposition temperature (Td) of PEI were improved by introducing SiO2 particles.The phase separation morphology of blends of 4

4'-diaminodiphenyl sulphone cured epoxy with PEI or PEI/SiO2composite was investigated by SEM and it showed that the introduction of SiO2 particles could reduce the size of the dispersion phase (PEI rich phase).Dynamic rheological measurement of epoxyresin(ER)/PEI/silica blends with different silica particle content was conducted at same isothermal temperature.The onset time of phase separation decreased as silica particles in the blend system increased because the silica particles could act as catalyst in the polymerization reaction and make the phase separation easier to occur.After that

the viscosity of system with higher particle concentration grew faster and made the phase separation process ends in an earlier stage.Dynamic mechanical thermal analysis (DMTA) and impact tests showed that using PEI/SiO2 as the modifier could enhance the modulus and toughness property of the epoxy resin system simultaneously.