Longer-scale segmental dynamics of amorphous poly(ethylene oxide)/poly(vinyl acetate) blends in the softening dispersion
Longer-scale segmental dynamics of amorphous poly(ethylene oxide)/poly(vinyl acetate) blends in the softening dispersion
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DOI：
10.1039/c0sm00633e
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发表时间：
2011-01
期刊：
影响因子：
3.4
通讯作者：
Xuebang Wu;Huaguang Wang;Changsong Liu;Zhen-Gang Zhu
中科院分区：
文献类型：
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作者：
Xuebang Wu;Huaguang Wang;Changsong Liu;Zhen-Gang Zhu
为研究聚氧乙烯(PEO)对聚乙酸乙烯酯(PVAc)在玻璃中松弛过程的影响，测定了PEO/PVAc共混物(PEO含量高达20wt%)的力学损耗随温度和频率的变化规律。结果表明，聚氧化乙烯组分对PVAc的α和α松弛模式有增塑作用，其中α模式为局部链段模式，α‘模式与软化分散体中较长链段的运动有关，由亚Rouse模式和Rouse模式组成。随着聚氧化乙烯浓度的增加，α和α模式均向低温方向移动。由于α模式和α‘模式的摩擦系数不同，PEO/PVAc共混物在整个温度范围内的时间-温度叠加破裂。得到了纯PVAc和PEO/PVAc共混物的α‘模式的单一主曲线，表明共混物中含有10~50个或更多主链键的链段尺寸不变。此外，还发现共混物中PVAc组分的α模的动力学行为通过松弛时间和松弛强度对温度的依赖呈现出特征的交叉。共混物的交叉温度Tb随PEO含量的增加而降低，而交叉弛豫时间不变，约为0.08 S，远长于10−7±1 S的α模式。根据耦合模型，认为这种交叉是由于Tb处分子间耦合的变化所致。
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 α and α′ relaxation modes of PVAc, where the α mode is ascribed to the local segmental mode and the α′ 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 α and α′ 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 α and α′ modes. A single master curve of the α′ 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 α′ 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 TB 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 α mode. According to the coupling model, the crossover is suggested to be due to the variation of intermolecular coupling at TB.