This article describes the preparation of novolac-type phenolic resin/silica hybrid organic-inorganic nanocomposite, with a sol-gel process. The coupling agent was used to improve the interface between the organic and inorganic phases. The effect of the structure of the nanocomposite on its physical and chemical properties is discussed. The coupling agent reacts with the resin to form covalent bonds. The structure of the modified hybrid nanocomposites was identified with a Fourier transform infrared spectroscope. The silica network was characterized by nuclear magnetic resonance imaging ( 29 Si NMR). Results revealed that Q 4 (tetrasubstituted) and T 3 (trisubstituted) are the dominant microstructures. The size of the silica in the phenolic resin was characterized with a scanning electron microscope. The size of the particles of inorganic silica in the modified system was less than 100 nm. The nanocomposite exhibited good transparency. Moreover, the thermal and mechanical properties exhibited significant improvement. The modified hybrid composite exhibited favorable thermal properties. The temperature at which a weight loss of 5% occurred increased from 281 to 350°C. The flexural strength increased by 6 -30%. The limiting oxygen index of the nanocomposite reached 37, and the Underwriters Laboratory test was 94V-0. Consequently, these materials possess excellent flame-retardant properties.

Abstract. Poly (St-MAn-APTES)/silica hybrid materials were successfully prepared from styrene (St), maleic anhydride (MAn) and tetraethoxysilane (TEOS) in the presence of a coupling agent 3-aminopropyltriethoxysilane (APTES), by freeradical solution polymerization and in situ sol-gel process. The TEOS content varied from 0 to 25 wt%. Fourier transform infrared spectroscopy and 29 Si nuclear magnetic resonance spectroscopy were used to characterize the structure of the hybrids (condensed siloxane bonds designated as Q 1 , Q 2 , Q 3 , Q 4 , with 3-aminopropyltriethoxysilane having mono-, di-, tri, tetra-substituted siloxane bonds designated as T 1 , T 2 and T 3 ). The results revealed that Q 3 , Q 4 and T 3 were the major microstructure elements in forming a network structure. The hybrid materials were also characterized by the methods of solvent extraction, Transmission Electron Microscopy (TEM), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) for determining the gel contents, particle size and thermal performance. The results showed that gel contents in the hybrid materials were much higher, the SiO2 phase were well dispersed in the polymer matrix, silicon dioxide existed at nanoscale in the composites, which had excellent thermal stability.