The present paper reports on an original experimental approach to the characterization of SWNT/polymer composites. This work deals with the multiscale characterization of nanocomposites. Covalently functionalized SWNTs were incorporated in a PMMA matrix using an in situ polymerization procedure. We show that their presence does not affect the radical polymerization process. Combining Brillouin and Raman spectroscopy, we were able to associate the obtained mechanical properties of the material at the macroscopic scale to the state of functionalization of the SWNTs within the polymer matrix.