Low-frequency librational vibrations, boson peak, and interchain interactions in a vitreous polymer

The IR and Raman spectra of plasticized poly(methyl methacrylate) (PMMA) are measured and analyzed in the frequency range 10–120 cm −1 , in which the absorption and scattering due to the individual (85–90 cm −1 ) and correlated librational vibrations (15–20 cm −1 , boson peak) preceding the appearance of relaxation dynamics manifest themselves. It is demonstrated that the presence of the boson peak as an indication of the solid-state behavior of the polymer material in the low-frequency spectra is associated with the correlation of librational vibrations not only inside macromolecules (in segments corresponding in length to the Kuhn segment) but also in segments of neighboring chains.