CONCENTRATION FLUCTUATION OF POLY(ETHYLENE OXIDE) IN A BLEND WITH POLY(METHYL METHACRYLATE) AND PHASE-SEPARATION BEHAVIOR STUDIED BY THE SPIN-LABEL METHOD

The electron spin resonance (ESR) line shape of nitroxide radical labels attached to polyethylene oxide) (PEO) chains in a blend with isotactic poly(methyl methacrylate) (PMMA) was studied as a function of temperature. Two spectral components with different rates of motion-a “fast” component and a “slow” component arising from the radicals-are observed in the temperature range 48-85 °C. It can be concluded that the fast and slow components should be attributed to nitroxide radicals trapped in the PEO-rich and PMMA-rich regions in the blend, respectively. From the temperature dependence of the fast spectral component, there are at least three relaxational regions: (I) the relaxation of PEO chains in the PEO- rich phase of a phase-separated system, (II) the disappearance of concentration fluctuation of PEO chains, and (III) the relaxation of PEO chains in a molecularly compatible system. Drastic broadening of the line width of the fast component was observed at 68 °C between regions I and II with rising temperature, whereas the width narrowed markedly at the same temperature with cooling. This reversible transition can be attributed to molecular mixing and phase separation. Thus an upper critical solution temperature (UCST) exists at 68 °C. In region II, the broadening of the line width also occurred more gradually with rising temperature than that in the phase transition. The concentration of PEO chains in region II appears to fluctuate with a frequency of ca. 109 s-1. © 1990, American Chemical Society. All rights reserved.