Longer-scale segmental dynamics of amorphous poly(ethylene oxide)/poly(vinyl acetate) blends in the softening dispersion

To study the influence of poly(ethylene oxide) (PEO) on the relaxation process of poly(vinyl acetate) (PVAc) in the glass to rubber softening dispersion, the mechanical loss behaviour of PEO/PVAc blends (with PEO contents up to 20 wt%) were measured as a function of temperature and frequency. It is shown that the PEO component has a plasticizing effect on the alpha and alpha' relaxation modes of PVAc, where the alpha mode is ascribed to the local segmental mode and the alpha' mode is related to the motion of longer chain segments in the softening dispersion, composed of the sub-Rouse modes and the Rouse modes. Both the alpha and alpha' modes shifted to lower temperatures with increase of PEO concentration. Time-temperature superposition breaks down for PEO/PVAc blends in the entire temperature range due to the different friction coefficients of the alpha and alpha' modes. A single master curve of the alpha' mode for pure PVAc and the PEO/PVAc blends is obtained, suggesting that the size of chain segments containing on the order of 10 to 50 or more backbone bonds does not change upon blending. Furthermore, the dynamics of the alpha' mode of the PVAc component in the blends is found to show a characteristic crossover through the temperature dependence of relaxation time and relaxation strength. The crossover temperature T-B decreases with increasing PEO content, while the crossover relaxation time for the blends is constant with a value about 0.08 s, much longer than 10(-7) (+/-) (1) s for the alpha mode. According to the coupling model, the crossover is suggested to be due to the variation of intermolecular coupling at T-B.