Raman scattering measurements are used to follow the modification of the vibrational density of states in a reactive epoxy{amine mixture during isothermal polymerization. Combining with Brillouin light and inelastic x-ray scattering measurements, we
analyze the variations of the boson peak and of the Debye level while the system passes from the uid to a glassy phase upon increasing the number of covalent bonds among the constituent molecules. We find that the shift and the intensity decrease of the boson peak are fully explained by the modification of the elastic medium throughout the reaction. Surprisingly, bond-induced modifications of the structure do not affect the relative excess of states over the Debye level.
