The modification of the vibrational density of states in a reactive epoxy amine mixture during isothermal polymerization at different temperatures was characterized by Brillouin and Raman scattering measurements. During the reaction, the system underwent the glass-transition passing from the liquid to the glassy phase. The relative variations of the boson peak (BP) and the elastic moduli were investigated. We found that the intensity variation and the shift of the BP could be completely explained in terms of the elastic medium transformation. A master curve of the spectra in the BP region can always be obtained both as a function of the reaction temperature and as a function of the reaction time. Moreover, the Brillouin light-scattering results gave evidence of the validity of a Cauchy-like relation for the real part of the elastic moduli measured at finite frequencies also in a relaxing regime. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 3672-3676, 2011