Poly(methyl methacrylate) (PMMA) containing aluminum-ethyl acetoacetate (EAA) [M5-Al(OBus)(EAA)(2)] was obtained from trialkoxysilane-functional poly(methyl methacrylate) and ethyl acetoacetate modified aluminum sec-butoxide via the sol-gel method. Infrared (IR), C-13 nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) were used to analyze the structures and properties of the hybrids with various proportions of PMMA. The effects of the PMMA content on the dynamics and stability of the M5-Al(OBus)(EAA)(2) hybrids were investigated in this study. The 1H spin-diffusion path length of the hybrids was in a nanometer scale as estimated from the spin-lattice relaxation time in a rotating frame (T-1 rho(H)). The apparent activation energies (E-a), evaluated by van Krevelens method, of the M5-Al(OBus)(EAA)(2) in thermo-oxidative degradation for random scission of EAA segments decreased roughly with increasing PMMA content.