  The scaling behavior of the so-called boson peak in glass-formers and its
relation to the elastic properties of the system remains a source of
controversy. Here, the boson peak in a binary reactive mixture is measured by
Raman scattering (i) on cooling the unreacted mixture well below its glass
transition temperature and (ii) after quenching to very low temperature the
mixture at different times during isothermal polymerization. These different
paths to the glassy phase are able to generate glasses with different amounts
of residual stresses, as evidenced by the departure of the elastic moduli from
a Cauchy-like relationship. We find that the scaling behavior of the boson peak
with the properties of the elastic medium --- as measured by the Debye
frequency --- holds for states in which the system is able to release internal
stress and breaks down in the presence of residual stresses. These findings
provide new insight into the boson peak behavior and are able to reconcile the
apparently conflicting results presented in literature.
