Nanocomposite materials prepared from radically photocurable hybrid sol-gel precursors have been widely developed within the last decade, especially to devise novel optical devices and coatings. For their synthesis, a preferential route has involved in the successive sol-gel process of acrylate trialkoxysilane precursors followed by radical photopolymerization. In contrast, this work presents an original one-step synthesis based on the association of two different photoinitiators (PIs) in the same formulation: the photolysis of a hydroxyphenylketone (radical PI) affords polyacrylate chains while that of a diaryl iodonium salt (cationic PI) generates powerful superacids catalyzing the sol-gel reactions of the alkoxy functions. The behavior of methacrylate and acrylate trimethoxysilane precursors was compared to highlight the effect of the organic moiety functionality on the reaction kinetics (Fourier transform infrared spectroscopy) and the film microstructure (C-13 and Si-29 solid-state nuclear magnetic resonance). Interestingly, evidence of local organization in these hybrid films was also given by X-ray analysis. In a last part, their thermomechanical properties were discussed thoroughly using a range of techniques: DSC, scratch-resistance test, nanoindentation. (c) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4150-4158, 2010