Syntheses And Properties Of Polymer/inorganic Nanocomposites

Polymer/inorganic nanocomposites have extracted extensive research interests due to their unique properties. The nanocomposites combine the advantages of the inorganic materials (rigidity, high thermal stability and unique optical, electronic and magnetic properties) and the organic polymers (flexibility, dielectric, ductility and processability), which is different with the single material and conventional composite materials. Moreover, these polymer/inorganic nanocomposites have potential application in electronic, optical, optoelectronic and nonlinear optical fields because the inorganic particles are well dispersed in polymer matrix in nanometer scale. The sol-gel route is an effective method for the preparation of polymer/inorganic nanocomposites in mild condition. The non-hydrolytic sol-gel route is also proved a useful method to synthesize polymer/inorganic nanocomposites and at least, it is a supplement for conventional sol-gel method. The non-hydrolytic sol-gel method has its advantages in the preparation of mixed inorganic oxides and in some water and acid sensitive reaction systems.In this paper, we prepare silica nanoparticles from water glass instead of TEOS, the most frequently used silica precursor. Mixed oxides based on silica and transition metal oxides are also synthesized using a combination of the hydrolytic and non-hydrolytic sol-gel methods. The obtained mixed oxides have greatly reduced photo-catalysis and aggregation tendency due to the formation of core-shell structures proved by the TEM image. The transition metal oxides with this kind of structure are useful in the preparation of polymer/inorganic nanocomposites. Besides the retained transparency, the nanocomposites exhibit improved thermal stability and special optical property compared with pure polymers. In this thesis, several kinds of polymers and inorganic materials were used to prepare the polymer/inorganic nanocomposites and their structures and properties are also extensively studied.(1) Polyimide/silica nanocomposites were prepared from water glass and polyamic acid (PAA), and the relationship between their structures and properties, such as thermal properties, mechanical properties, optical properties and thermal expansion, were studied. TGA results indicated the improved thermal stability of the nanocomposites. The coefficients of thermal expansion (CTE) of polyimide were effectively reduced by the addition of silica nanoparticles and they could be further reduced after suitable structure control of polyimide/silica nanocomposites. This kind of nanocomposites extends their application in micro-electronic fields.(2) Silica/zirconia and silica/titania mixed oxides were prepared in a milder and more controllable reaction condition via a combination of hydrolytic and non-hydrolytic sol-gel methods. FT-IR spectrum confirms that there are covalent bonds between polymer matrix and inorganic moieties. TEM images indicate the formation of core-shell structure of silica and titania components. This structure is favorable for the synthesis of polymer/transition metal oxide nanocomposites.(3) The well dispersion of silica/titania mixed oxide in polyimide matrix is caused by the coordinate interaction between titania nanoparticles and polyimide main chains, which maintains the transparency of the nanocomposites. The thermal stability of polyimide is greatly reduced by the introduction of titania materials. But it can be compensated partly by adding silica components due to the formation of well controlled structure between two inorganic components. These results also indicate that the optical properties and surface resistances can be accurately modulated by the inorganic content in the nanocomposites and titania content in the mixed oxides.(4) Compared with pure PMMA, PMMA/silica/zirconia and PMMA/silica/titania nanocomposites exhibit high thermal stability and thermo-oxidative stability even at very low inorganic content because of the special electronic configuration of zirconia and titania. The kinetics analysis for the thermal degradation of the nanocomposites indicates that the apparent activation energies (Ea) of the nanocomposites containing transition metal oxides are much higher than that of...