In this work we have investigated how the dynamics of poly(vinyl methyl ether), PVME, changes by blending with deuterated polystyrene. The experimental techniques used were dielectric spectroscopy, quasielastic neutron scattering, and 13 C nuclear magnetic resonance. By means of these techniques, the dynamics of the poly(vinyl methyl ether) units in the blends can be selectively investigated in a huge time range (10 1 -10 -11 s). Two different blend compositions have been investigated. The main relaxation processes observed in this range are the secondary -process and the segmental R-relaxation. It turns out that the -relaxation is not affected by blending. The data analysis procedure followed by us in the case of the R-process is based on the assumption that the dynamics of the PVME segments in the blends is a superposition of dynamical processes with the same shape as that in pure PVME, but with the relaxation times distributed due to the presence of concentration fluctuations. From this analysis we found that, in the blends, and in pure PVME as well, the results obtained by means of the different techniques can consistently be described with the same set of parameters. Moreover, the temperature dependence of the distribution of relaxation times in each blend composition can be accounted for by a single, temperature-independent, Gaussian distribution of the Vogel-Fulcher temperature, T 0, the average and the variance of the distribution increasing as the PVME concentration decreases. Our results suggest that a significant number of PVME segments in the blends move faster than in pure PVME. Furthermore, our results strongly indicate that each polymer component of the blend exhibits very different R-relaxation rates, i.e., different "glass transitions". Several implications of these results concerning the usually accepted ideas of polymer blend dynamics are outlined.

In this article we report on the investigation of the dynamics of poly(vinyl alcohol) (PVA) and PVA-based composite films by means of dielectric spectroscopy and dynamic mechanical thermal analysis. Once the characterization of pure PVA was done, we studied the effect of a nanostructured magnetic filler (nanosized CoFe 2 O 4 particles homogeneously dispersed within a sulfonated polystyrene matrix) on the dynamics of PVA. Our results suggest that the ␣-relaxation process, corresponding to the glass transition of PVA, is affected by the filler. The glass-transition temperature of PVA increases with filler content up to compositions of around 10 wt %, probably as a result of polymer-filler interactions that reduce the polymer chain mobility. For filler contents higher than 10 wt %, the glass-transition temperature of PVA decreases as a result of the absorption of water that causes a plasticizing effect. The ␤and ␥-relaxation processes of PVA are not affected by the filler as stated from both dynamic mechanical thermal analysis and dielectric spectroscopy. Nevertheless, both relaxation processes are greatly affected by the moisture content.

The relaxational dynamics of the ambient pressure phases of ethyl alcohol are studied by means of measurements of frequency dependent dielectric susceptibility. A comparison of the ␣ relaxation in the supercooled liquid and in the rotator phase crystal indicates that the molecular rotational degrees of freedom are the dominant contribution to structural relaxation at temperatures near the glass transition, the flow processes having lesser importance. Below the glass transition a secondary ␤ relaxation is resolved for the orientational and structural glasses. Computer molecular-dynamics results suggest that localized molecular librations, strongly coupled to the low-frequency internal molecular motions, are responsible for this secondary relaxation. ͓S0163-1829͑99͒00914-5͔

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The dielectric -relaxation of the poly(epichlorohydrin)/poly(vinyl methyl ether) miscible system is investigated in the frequency range 10-2-106 Hz. This polymer blend has the particularity that the components have nearly coincident glass-transition temperatures. We found that the relaxation spectra of these blends can be well described by the Kohlrausch-Williams-Watts law, the shape parameter being nearly temperature independent. This means that the dynamical heterogeneity commonly reported for the -relaxation of miscible polymer blends is not found in this system. Our results suggest that the main reason for the dynamical homogeneity observed in the blend investigated in this work is that the neat components have nearly coincident Tg values. This can be considered as proof of the relevance of the difference between Tg of the blend components in the origin of the heterogeneous behavior commonly observed for the polymer blend dynamics in the -relaxation range.