Component relaxation dynamics in a miscible polymer blend: poly(ethylene oxide)/poly(methyl methacrylate)

Relaxation dynamics in the miscible blend of poly(ethylene oxide) (PEO) and poly (methyl methacrylate) (PMMA) is studied subsequent to a linear step strain using the simultaneous measurement of infrared dichroism and birefringence. Blends ranging in composition from 20-60 wt.% PMMA are prepared from nearly monodisperse PMMA (M sub w = 337 000), PEO (M sub w = 112 000), and deuterated PEO (M sub w = 122 000). IR dichroism in these blends is governed solely by the segmental orientation of the deuterium-labled PEO and therefore may be used to recover the characteristic PEO relaxation time. Birefringenece, on the other hand, is a measure of both PEO and PMMA orientation, and it is shown that from the long-time behavior of this observable the characteristic relaxation time of PMMA may be recovered. Component relaxation times computed in this fashion are monitored as functions of blend composition and T-T sub g . To extend the range of compositions and provide a basis for comparison to the pure state, results from dynamic mechanical experiments on the pure components and 70 and 80% PMMA blends are included in the analysis. It is observed that the blend components maintain distinct relaxation times but that the presence of dissimilar chains certainly affects component relaxation behavior. PEO relaxation times are found to be more strongly composition dependent and pass through a maximum near 40-50% PMMA. Several mechanisms possibly responsible for this behavior are discussed. In addition, it was observed that for PMMA-rich blends each component manifests a separate temperature dependence, while for PEO-rich systems the blends appear to be thermorheologically simple.