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Molecular Motion of Polymers under Supercritical Carbon Dioxide

超临界二氧化碳下聚合物的分子运动

基本信息

批准号：
14550843
负责人：
SAITO Hiromu
金额：
$ 2.24万
依托单位：
Tokyo University of Agriculture And Technology
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2003
项目状态：
已结题

项目摘要

In order to deeply understand the molecular motion of polymers under supercritical C0_2, we carried out in-situ measurements of dielectric loss e" in PMMA over a wide frequency f range at various temperatures under CO_2. The PMMA under ambient pressure shows an Arrhenius behavior and a bend at around Jig. The bend may arise from the change in the mode of motion at T_g ; i.e., the motion above T_g is the αβ process while that below Jig is the β process. The PMMA under CO2 also exhibits an Arrhenius behavior and the plots also bend. The bending temperature shifts to lower temperature with increasing CO_2 pressure. This may be ascribed to the decrease of Jig with increasing CO_2 pressure due to the plasticizing effect by CO_2. The interesting result here is that the f_<max> below T_g also becomes higher with increasing CO_2 pressure, suggesting that the local motion such as the side group rotation is also accelerated by the plasticizing effect. After injecting C0_2, the shift of the peak position was leveled off and the shape of the peak became narrower with time, suggesting that the density fluctuation is homogenized with time and the acceleration of the molecular motion is leveled off due to saturation of the absorbed CO_2 in PMMA. The peak height increases with time while the peak position remains constant. The peak height under CO_2 became 2 times larger than that under ambient pressure having the same f_<max>. The increase of the peak height may be ascribed to the acceleration of the cooperative motion between adjacent chains due to a change in chain conformation from random coil to a locally ordered state.

为了深入了解聚合物在超临界CO_2中的分子运动，我们在CO_2中对PMMA在宽频率f范围内的介电损耗e”进行了现场测量。PMMA在环境压力下表现出阿耳忒弥斯行为，并在夹具附近出现弯曲。该弯曲可由T_g处运动模式的变化引起;即，T_g以上的运动为αβ过程，T_g以下的运动为β过程。在CO2下的PMMA也表现出阿耳忒弥斯行为，并且图也弯曲。随着CO_2压力的增加，弯曲温度向低温方向移动。这可能是由于CO_2的增塑作用使Jig随CO_2压力的增加而减小。有趣的结果是，<max>随着CO_2压力的增加，玻璃化转变温度以下的f_g也变大，这表明塑化作用也加速了侧基转动等局部运动。注入CO_2后，随着时间的延长，峰位的移动趋于平缓，峰形变窄，说明PMMA中吸收的CO_2饱和，使密度波动趋于均匀，分子运动加速趋于平缓。峰高随时间增加，而峰位保持不变。CO_2下的峰高比常压下的峰高大2倍<max>。峰高的增加可以归因于由于链构象从无规卷曲到局部有序状态的变化而加速了相邻链之间的协同运动。