Compositional Dependence of Segmental Dynamics in a Miscible Polymer Blend

Abstract

The segmental motion of each species in polyisoprene/poly(vinylethylene) (PI/PVE) miscible blends is studied at three different compositions using two-dimensional deuteron exchange NMR (2D 2H NMR). The individual species exhibit widely different mean mobilities and broad mobility distributions near the glass transition of each blend. As the PVE content increases, both the difference in mean mobilities between the two species and the width of the mobility distribution for both components increase. The change in these two types of dynamic heterogeneity with PVE content appears to produce the anomalous broadening of the glass transition. The mean reorientational correlation times of each component can differ by 2 orders of magnitude under identical conditions. This difference can be described in terms of distinct effective glass transition temperatures, Tg*, for the two species. The separation between the two effective glass transition temperatures increases almost monotonically with PVE content, consistent with the more pronounced thermorheological complexity of blends rich in PVE. The individual Tg*' s also exhibit a different compositional dependence from that of the calorimetric Tg of the blend observed by differential scanning calorimetry (DSC). This behavior can give rise to the complex compositional dependence of individual mobilities, apparent when the mobilities are compared at the same T -Tg with respect to the DSC Tg of the blend.

Unusual Component Dynamics in Poly(ethylene oxide)/Poly(methyl methacrylate) Blends As Probed by Deuterium NMR

“…The dashed line is τ seg for neat PI, and above that the thicker lines are the VFTH fits to the NMR data of the three blends (in ascending order with increasing PVE content). Comparing these data with τ seg from the lower temperature NMR data 36 (upper part of Figure 3), it is evident that the composition dependence of τ seg is much reduced at the high frequencies and higher temperatures of the measurements of Min et al 37 Substituting in eq 2 the "average" τ seg given by Min et al for τ and the "average" KWW exponent ) 0.54 of neat PI also from Min et al (written as 1 -n in eq 2), the independent relaxation time τ 0 is calculated (using t c ) 2 × 10 -12 s) as a function of temperature. With the known τ 0 , we calculate the most probable segmental relaxation time τ(n ) of PI in the PI/PVE blends by eq 5 with (1 -n ) exactly equal to given in Table 4 of Min et al, 37 i.e., 0.50, 0.47, and 0.44 respectively for the 70/30, 50/50, and 30/70 PI/PVE Shown by the lowest solid line is the independent relaxation time for neat PI calculated using n ) 0.46 ( ) 0.54), the value reported by Min et al 37 Also shown are the most probable relaxation times calculated from eq 5 for the 70% PI (2, n ) 0.54), 50% PI (0, n ) 0.53), and 30% PI (b, n ) 0.56).…”

“…36 In the case of PEO, this precludes measurements on the amorphous state because of crystallization. However, dielectric loss spectra of the chemically similar PPO were reported by Williams et al 42 The R-loss peak, shown in Figure 4, is independent of temperature over the range studied.…”

Molecular dynamics of polyisoprene/polystyrene oligomer blends: The role of self-concentration and fluctuations on blend dynamics

“…This view of polymer blend dynamics was proposed by Zetsche and Fischer 4 and further developed in subsequent studies that extended the concept of concentration fluctuations beyond a Gaussian form, to capture experimental and simulation data. [5][6][7][8][9][10][11][12][13][14][15] Some of the aforementioned studies added the effect of self-concentration, first introduced by Chung et al 16 and further elaborated by the Lodge-McLeish (LM) model. 17 According to this concept, each segment of a specific component A is experiencing an environment that is enriched to A due to chain connectivity.…”

“…17 According to this concept, each segment of a specific component A is experiencing an environment that is enriched to A due to chain connectivity. 16 To create a quantitative formalism, it is necessary to select an appropriate lengthscale over which self-concentration and fluctuations in composition control segmental dynamics. The success of these theoretical models to capture qualitatively experimental findings, fueled extensive studies aiming to offer a quantitative prediction of dynamics in polymer blends.…”

Dynamics of PEO in Blends with PMMA: Study of the Effects of Blend Composition via Quasi-Elastic Neutron Scattering

“…The extreme difference in mobility between PEO and PMMA is a feature unique to this blend system. The dynamics of polyisoprene [PI] and poly(vinyl ethylene) [PVE] are separated by 2-5 orders of magnitude, 13,14 …”