  The dynamics of polypropylene glycol, both neat and attached to silica
nanoparticles, were investigated using elastic neutron backscattering and
dielectric spectroscopy. The mean square displacement measured by the former is
suppressed by the particles at temperatures corresponding to a dielectric
secondary relaxation (that involves only a portion of the repeat unit) and the
segmental relaxation (glass transition). Despite the suppression of the
displacements, the motions are faster in the nanocomposite, primarily due to
poorer packing (lower density) at the particle interface. At very low
temperatures we discovered a new dynamic process in the polymer. Reflecting its
very local nature, this process is unaffected by attachment of the chains to
the silica.
