Localized picosecond-scale process in glassy poly(methyl methacrylate) farbelow T-g - art. no. 144202

We carried out incoherent and coherent inelastic neutron scattering on glas sy poly(methyl methacrylate) in a wide scattering vector range up to 4.9 An gstrom (-1) with a high-energy resolution of 0.16 meV to investigate low-en ergy modes: the so-called boson peak and the picosecond-scale process. Firs t, we studied the basic features of the two modes in the incoherent measure ments and found that they are similar to those reported for many glass-form ing materials. In the coherent scattering measurements, focusing on the Q d ependence of the inelastic scattering intensity, we found that the boson pe ak and picosecond-scale process modes do not move in phase at a length scal e of similar to7 Angstrom, while the motional coherency is preserved betwee n neighboring side chains in a polymer. These observations suggest that the boson peak and picosecond-scale process are localized modes on two monomer s within a polymer chain. The intrachain localization becomes more pronounc ed with increasing the excitation energy.