  The local segmental and global dynamics of a series of polypropylene glycol /
silica nanocomposites were studied using rheometry and mechanical and
dielectric spectroscopies. The particles cause substantial changes in the
rheology, including higher viscosities that become non-Newtonian and the
appearance of stress overshoots in the transient shear viscosity. However, no
change was observed in the mean relaxation times for either the segmental or
normal mode dynamics measured dielectrically. This absence of an effect of the
particles is due to masking of the interfacial response by polymer chains
remote from the particles. When the unattached polymer was extracted to isolate
the interfacial material, very large reductions in the relaxation times were
measured. This speeding up of the dynamics is due in part to the reduced
density at the interface, presumably a consequence of poorer packing of
tethered chains. In addition, binding of the ether oxygens of the polypropylene
glycol chains truncates the normal mode, which shifts the corresponding
relaxation peak to higher frequencies.
