Thermal Expansion of Amorphous Polymers at Atmospheric Pressure. I. Experimental
Thermal Expansion of Amorphous Polymers at Atmospheric Pressure. I. Experimental
复制标题
无定形聚合物在大气压下的热膨胀。
DOI：
10.1021/ma60036a022
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发表时间：
1973
期刊：
影响因子：
5.5
通讯作者：
R. Simha
中科院分区：
文献类型：
--
作者：
P. S. Wilson;R. Simha
结论有人指出，从 ET-24-1 到 ET-28-1，定向行为发生了巨大变化。 ET-24-1 中的任何一段都几乎没有保持方向。在ET-28-1、ET-31-1和ET-38-1中，保持了相对较高的取向度，特别是在硬段中。这表明这与 ET-28-1 中互锁硬段结构域的发展有关，而 ET-24-1 中不存在这种互锁硬段结构域。在 ET-24-1 中，独立的硬域允许两个部分的方向广泛松弛。在ET-28-1中，取向松弛受到硬链段互连形态的严重限制。柔性的软链段可以更大程度地松弛，但它们也通过与硬链段的共价键合而受到限制。因此，取向行为随成分的第一次变化发生在形态从独立的硬域变为互锁结构的点。一旦形成互锁的亚晶硬区，由于硬区体积分数的变化，取向行为仅发生微小变化。这些材料的基本机制是在所有伸长率下两个片段在拉伸方向上的取向（正取向）逐渐增加。 Wilkes 基于对可比较的非晶嵌段聚氨酯的低角度 X 射线研究得出了类似的结论。 15当结晶度（由强烈的高温DSC吸热12的存在所决定）被引入硬块时，观察到取向机制的根本变化。虽然存在的非晶段仍然像以前一样取向，但结晶区域在低伸长率下显示出段的横向（负）取向。这可以可视化为结晶区域拉伸方向的取向
ConclusionsIt has been pointed out that there is a drastic change in orientation behavior in going from ET-24-1 to ET-28-1. Very little orientation is held in either segment in ET-24-1. In ET-28-1, ET-31-1 and ET-38-1, relatively high degrees of orientation are maintained, particularly in the hard segments. It is suggested that this is connected with the development of interlocking hard segment domains in ET-28-1 which do not exist in ET-24-1. In ET-24-1, the independent hard domains allow extensive relaxation of the orientation in both segments. In ET-28-1, relaxation of orientation is severely restricted by the interconnecting morphology of the hard segments. The flexible soft seg-ments can relax to a greater degree, but they too are re-strained by covalent bonding to the hard segments. The first change in orientation behavior with composition thus occurs at the point where the morphology changes from independent hard domains to an interlocked structure. Once the interlocked subcrystalline hard re-gions are formed, only minor changes in orientation be-havior due to the changing volumefraction of hard seg-ment occur. The basic mechanism for these materials is an increasing orientation of both segments into the stretch direction (positive orientation) at all elongations. A simi-lar conclusion based upon low-angle X-ray studies on comparable noncrystalline segmented polyurethanes was made by Wilkes. 15A fundamental change in orientation mechanism is observed when crystallinity (as determined by the existence of an intense high temperature DSC endotherm12 is intro-duced into the hard blocks. While the noncrystalline seg-ments present still orient as before, thecrystalline regions show a transverse (negative) orientation of the segments at low elongations. This may be visualized as an orientation into the stretch direction of the crystalline regions