Miscible blends of perdeuteriopoly(ethylene oxide) (d4PEO) and poly(methyl methacrylate) (PMMA) were studied using deuterium NMR over the concentration range of 0.5−30% d4PEO using 2−4 Larmor frequencies ranging from 31 to 76 MHz. Spin−lattice relaxation times and line widths were measured from 300 to 475 K. Over this range PEO is liquidlike or rubbery in terms of its dynamics even though many of the measurements are below the blend glass transition temperature. There is no indication of the DSC glass transition in terms of a jump in either the spin−lattice relaxation times or the line widths. A model suitable for a rubber solid was used to interpret the spin−lattice relaxation times in terms of segmental motion and backbone libration. Segmental correlation times for d4PEO fall in the nanosecond range with a very broad distribution of correlation times described by a KWW β of about 0.27. The segmental dynamics of d4PEO are 12 orders of magnitude faster than PMMA segmental dynamics for a 3% d4PEO blend near the blend T g. Over the temperature range studied, d4PEO segmental dynamics are nearly independent of composition for blends from 0.5% to 30% d4PEO. At the lowest concentration studied, d4PEO is in the dilute solution range; this eliminates intermolecular concentration fluctuations as an explanation of the rapid d4PEO dynamics. These observations are unusual for miscible polymer blends and cannot be described by current models.

The Lodge–McLeish model of miscible blend dynamics is compared to literature data for the segmental or terminal dynamics of components in six different miscible polymer mixtures. In most cases, the model successfully fits the experimental data for a given component with a parameter φself, which is independent of temperature and composition. In most cases, the fitted value of φself is close to the model prediction, providing some support for the assumption that the Kuhn length is the relevant length scale for dynamics in miscible polymer mixtures. In other cases, the model either fits the data with φself values much different than those expected based on the Kuhn length, or fails to fit the experimental data for any value of φself. Using the Fox equation as input to the Lodge–McLeish model provides a better description of the experimental data than using the measured mixture Tg values.

We have performed NMR spin-lattice relaxation experiments and molecular dynamics (MD) computer simulations on atactic polystyrene (a-PS). The segmental correlation times of three different molecular weight a-PS (M n ) 1600, 2100, 10 900 g/mol) were extracted from NMR by measuring the 2 H spin-lattice relaxation times (T1) over a broad temperature range (390-510 K). MD simulations of an a-PS melt of molecular weight 2200 g/mol were carried out at 475, 500, and 535 K. Comparisons between experiments and simulations show that the MD simulations reproduce both the shape of the P 2(t) orientation autocorrelation function and its temperature dependence, while the simulated segmental correlation times are slower than experimental results by a factor of 1.8. If the simulations are rescaled by this factor, they reproduce both the experimental T 1 values and the slight difference in dynamics between the backbone and side group of PS.

13C NMR has been used to investigate the segmental dynamics of isolated polyisoprene (PI) chains in host matrices of polybutadiene (PB), poly(vinylethylene) (PVE), and polystyrene (PS). In the dilute regime, where intermolecular concentration fluctuations are minimal, the segmental dynamics of isolated PI chains do not become slaved to the segmental dynamics of the host matrix but are significantly biased toward the dynamics of pure PI. Using the framework of the Lodge−McLeish model, it is shown that self-concentration effects can account for the dilute PI segmental dynamics. The value of self-concentration was determined to be 0.41 for PI segmental dynamics in PVE blends, a value which agrees with findings at higher compositions and which is also in reasonable agreement with the Lodge−McLeish prediction (0.45 for PI). In contrast, the observed self-concentration values for dilute PI blends with PS (∼0.20) and PB (∼0.85) do not agree with the model prediction of 0.45. These results indicate the importance of self-concentration in understanding the component dynamics and the rheology of miscible polymer blends.

2H NMR relaxation time measurements have been used to investigate the segmental dynamics of polystyrene chains in six miscible polymer blends in the limit of low polystyrene concentration. These data are combined with previously reported results for the segmental dynamics of dilute polystyrene chains in four solvents. Polystyrene dynamics in these 10 hosts are strongly correlated with the glass transition temperature T g of the host, but the dilute chain dynamics are not slaved to the host matrix dynamics. The Lodge−McLeish model, using a single value for the self-concentration φself = 0.35, reasonably describes polystyrene segmental dynamics in all 10 hosts and also describes previously reported dynamics of dilute polyisoprene chains in four miscible blends. The dilute polystyrene segmental dynamics can be more accurately described if φself is allowed to depend on blending partner, with the resulting variation of φself from 0.14 to 0.48.