Rapid poly(ethylene oxide) segmental dynamics in blends with poly(methyl methacrylate)

Miscible blends of perdeuteriopoly(ethylene oxide) (d(4)PEO) and poly(methyl methacrylate) (PMMA) were studied using deuterium NMR over the concentration range of 0.5-30% d(4)PEO 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 d(4)PEO fall in the nanosecond range with a very broad distribution of correlation times described by a KWW beta of about 0.27. The segmental dynamics of d(4)PEO are 12 orders of magnitude faster than PMMA segmental dynamics for a 3% d(4)PEO blend near the blend T-g. Over the temperature range studied, d(4)PEO segmental dynamics are nearly independent of composition for blends from 0.5% to 30% d(4)PEO. At the lowest concentration studied, d(4)PEO is in the dilute solution range; this eliminates intermolecular concentration fluctuations as an explanation of the rapid d(4)PEO dynamics. These observations are unusual for miscible polymer blends and cannot be described by current models.