Poly(methyl methacrylate)-silica hybrid materials, P(MMA-MA5)-SiO2 or P(MMA-GMA5)-SiO2, were synthesized from the in situ reaction of the methyl methacrylate (MMA) with maleic anhydride (MA) or glycidyl methacrylate (GMA), then hydrolyzed with 3-aminopropyl methyl diethoxysilane (APrMDEOS) and tetraethoxysilane (TEOS) by a sol-gel process. The thermal stability and the apparent activation energies (E-a) of the PMMA moieties in the hybrids under air and nitrogen, evaluated by van Krevelen's method, were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). P(MMA-GMA5)-SiO2 hybrids with the flexible chain of the coupling agent had the lower glass transition temperature (T-g) and E-a. Moreover, the structure of the coupling agent influences the thermal and thermo-oxidative degradation of the PMMA within the hybrids.