Poly(acrylic acid)-silica composites have been prepared by two different methods and thermally characterized. The glass transition temperature (T-g of the PAA-SiO2 system prepared by mixture method was found to be 120 degrees C irrespective of the type and amounts of silica involved in this work. However, the T-g varied between 132 degrees C and 113 degrees C in the systems prepared by polymerization reaction depending upon the type of silica and percentage conversion. The composites prepared by mixture and polymerization method have been investigated by using thermogravimetry (TGA) to follow the kinetics of anhydride formation and thermal degradation reactions. The activation energy of thermal anhydride formation and thermal degradation reaction was not found to change very much with ratio of PAA-SiO2 when the composites were prepared by simple mixing. For the composites prepared by polymerization method the activation energy of anhydride formation and thermal degradation reaction were observed to change with percentage conversion. (C) 1998 John Wiley & Sons, Inc.