J. Zhao et al., DEUTERIUM NMR-STUDY OF PHENYL GROUP MOTION IN GLASSY POLYSTYRENE AND A BLEND OF POLYSTYRENE WITH POLYPHENYLENE OXIDE, Macromolecules, 28(11), 1995, pp. 3881-3889
Deuterium solid echo line shapes were measured as a function of temper
ature and echo delay time on glassy polystyrene and a blend of polysty
rene with poly(2,6-dimethyl-1,4-phenylene oxide). The spectra were str
ongly temperature dependent from room temperature to the glass transit
ion, indicating motion on the time scale of tens to hundreds of micros
econds. The line shape signature of pi flips is present in these spect
ra. The time scale and temperature range overlap the beta process seen
in dynamic mechanical spectroscopy on both pure polystyrene and in th
e blend. A quantitative interpretation of the phenyl dynamics was base
d on a simultaneous description of phenyl group rotation which allows
for small angle jumps and pi flips. A fairly broad distribution of cor
relation times was introduced through the use of the stretched exponen
tial correlation function. The quantitative interpretation reinforces
the time/temperature overlap of the phenyl group motion with the beta
process though the apparent activation energies from different approac
hes are difficult to compare due to the limited temperature range and
the overlap with the alpha process.