The local dynamics of the low-T(g) component in a polymer blend, dynamically asymmetric poly(styrene)-poly(vinyl methyl ether) (PS-PVME), is studied below the glass transition, via dielectric relaxation spectroscopy. A particular attention has been paid to blends with a high PS content (PS weight fraction higher than 50%). A relaxation process, slower than the localized motions inducing the PVME secondary relaxations, is detected. Even though these blends fall out of equilibrium in this temperature regime, the structural recovery process is not efficient on the time scale of this PVME motional process. This relaxation is attributed to rather localized, weakly cooperative PVME motions resulting from the topological constraints imposed by the frozen PS chains.
The segmental dynamics of amorphous poly(dimethylsiloxane) (PDMS) in a lamellar poly(styrene)−poly(dimethylsiloxane) diblock (PS−PDMS) is investigated by means of broadband dielectric
spectroscopy. Because of the absence of normal mode in PDMS, we have been able to analyze the low-frequency side of the α-relaxation in detail. The characteristic time of the segmental dynamics is found
to be significantly higher than that in a PDMS homopolymer. In addition, the dielectric loss peak displays
a pronounced broadening in the low-frequency side as compared with that observed in pure PDMS. We
showed that the ε‘ ‘(ω) curves could be well described assuming two types of PDMS segments depicting
qualitatively distinct segmental dynamics. In one case, the dielectric response is similar to that one of
the amorphous constrained phase in a cold-crystallized PDMS homopolymer. For the other segments,
the dielectric behavior appears close to that one of an amorphous PDMS homopolymer. However, some
differences remain indicating a significant gradient of mobility within this second type of PDMS segments.
We explain all these findings by considering a simple picture of the PDMS segments in the PS−PDMS
lamellar mesophase.
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