Rapid Poly(ethylene oxide) Segmental Dynamics in Blends with Poly(methyl methacrylate)

Abstract

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.

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

“…9 This is not the case for the 10 wt % blend where PEO moves much slower than would be expected if the same composition dependence was continued. This could be due to labeling issues or an increasing contribution from the collective dynamics of deuterated PMMA.…”

“…In addition, NMR data show that the slow process is quite stretched, with values of 0.28. 9 At the spatial scale provided in the figure, values from QENS range between 0.35 and 0.40 at low temperature and increase to between 0.5 and 0.6 at the highest temperatures measured. Also shown in Figure 6 are times from a recent QENS study on PEO dynamics in this system.…”

“…The data are best described for the 20% blend. For this comparison, we required VTF parameters for PEO 9 [B ) 748.5 K, T 0 ) 166 K, and τ ) 0.095 ps] and parameters for the calculation of φ self [C ∞ ) 6.7, M 0 ) 44 g/mol, k ) 3, F ) 1.07 g/cm 3 , N AV ) 6.023 × 10 23 mol -1 , and l K ) 1.1 × 10 -7 cm]. 51 As the spatial scale is decreased, φ self ) 0.22 no longer describes the data, although it can be correlated by allowing φ self to vary.…”

“…Although the difference in the blend is smaller than that between the pure components, component mobilities remain widely separated. A study 9 using 2 H nuclear magnetic resonance [NMR] suggests that segmental relaxation times of PEO may be up to 12 orders of magnitude faster than those of PMMA near the blend T g . The extreme difference in mobility between PEO and PMMA is a feature unique to this blend system.…”

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

“…In particular, when different theories purport to explain the same phenomena, new experimental facts are crucial. The recent deuterium NMR study of blends of deuterated poly(ethylene oxide) (d 4 PEO) and poly-(methyl methacrylate) (PMMA) by Lutz et al 1 is such an example in the field of component dynamics of miscible polymer blends. The authors found that the segmental dynamics of d 4 PEO are nearly independent of composition for blends ranging from 0.5% to 30% d 4 -PEO, over the temperature range studied, and are about 12 orders of magnitude faster than the dynamics of PMMA for a 3% d 4 PEO blend near its glass transition temperature, T g .…”