| Abstrakt: |
The local and cooperative dynamics in atactic (a-PS) and syndiotactic (s-PS) polystyrene were studied by broadband dielectric spectroscopy. Besides the known -relaxation, two additional relaxation processes 1and 2were revealed in various samples of a-PS and s-PS films cast from solvent solutions. These new dynamic processes show Arrhenius behavior, a common activation energy around 80 kJ/mol, and cross the -relaxation region without merging, indicating a molecular origin being phase-separated from the amorphous PS fraction. By Fourier transform infrared spectroscopy (FTIR) measurements, a clear link between the existence of T2G2helix conformation and the occurrence of the 1- and 2-processes was established. Symmetry arguments and systematic differences in the relaxation parameters between a-PS and s-PS favor the assignment of the fast, 1, process to a helix defect mechanism (helix inversion), while the slow mode, 2, likely originates from cooperative helix inversion events that would point to spatially organized aggregates of helices, as suggested earlier for PS gels. The occurrence of such solvent-induced structures and their dynamics might have important implication for the interpretation of Tgreductions found in ultrathin PS films. |
