Time-temperature superposition segmental motions

Two-dimensional deuteron NMR was used to analyze miscibility in blends of poly-1,4-polyisoprene with polyvinylethylene (PIP/PVE) [Arendt et al., 1994 Chung et al, 1994]. The blends were prepared by casting 3 wt% toluene solution. The rate of reorientation as a function of temperature near T was determined for both components. It was found that the system is miscible, but the glass transition is broad owing to the wide distribution of segmental motions arising from the differences in the rates of the two polymers. As a result, the PIP/PVE blends were found to be rheologically complex. In spite of miscibility the time-temperature superposition was found to be invalid. 

Both cis-polyisoprene (PI) and poly(vinyl ethylene) (PVE) have the type-B dipoles perpendicular to the chain backbone, and PI also has the type-A dipoles parallel along the backbone (cf. Figure 3.2). The dielectric relaxation detects the fluctuation of these dipoles, as explained in Section 3.2.2. The fluctuation of the type-B dipoles is activated by the fast, local motion of the monomeric segments, which enables the dielectric investigation of this motion. In contrast, the slow dielectric relaxation of PI due to the type-A dipoles exclusively detects the fluctuation of the end-to-end-vector R (see Equation 3.23). These dielectric features of PI and PVE are clearly noted in Figure 3.11, where the e" data are shown for a PI/PVE blend with the component molecular weights Mp, = 1.2 x 1(P and Mpyp = 6 x 1(P and the PI content rvpi = 75 wt% (Hirose et al., 2003). The data measured at different temperatures are converted to the master curve after the time-temperature superposition with the reference temperature of T, = -20°C, as explained later in more detail. The three distinct dispersions seen at high, middle, and low... 

Fig. 2.33. A comparison of the retardation spectra L of a high molecular weight PS (filled triangles), a solution of 25% PS in TCP (open squares) and PIB (filled circles). The shift factors are arranged such that the maximum of the first peak occurs at the same reduced frequency for all three samples. Downward vertical shifts by 0.869 and 1.39 of logio L have been applied to data for PS and the 25% PS solution, respectively, in order to make all data have about the same height at the first maximum. The disparity in width of the softening dispersion of bulk PS and PIB is clear. The small peak near the bottom (dashed line) is the contribution to L from the local segmental motion in bulk PS. The inset shows isothermal tan 8 data of PIB in the softening region at -66.9 °C, and tan 8 of the solution of 25% PS in TCP obtained from a reduced recoverable-compliance curve after applying time-temperature superposition to the limited isothermal data.

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