Inelastic neutron scattering experiments on polyurethane: Microscopic origin of the β relaxational process

We present an experimental investigation of the relaxational processes related to the glass transition in a family of polymers where the molecular architecture can be varied. The samples are crosslinked polyurethanes where the crosslink density, as well as the length between crosslinks, can be modified. Inelastic neutron scattering was used to determine the relaxation times in the 10 −8 -10 −12 s range. The times measured by this technique split from the structural relaxation determined at lower frequencies. Inelastic neutron scattering is sensitive to a secondary relaxation process, which is in the continuity of the β process probed by dielectric spectroscopy. Moreover, the dependence on the microscopic parameters of this process suggests that the corresponding relaxing entity can be identified as a smali portion of the arms of the triol, in agreement with the explanation suggested independently for the relaxational process investigated by dielectric measurements.