MOLECULAR MOTION IN POLYAMIDES
MOLECULAR MOTION IN POLYAMIDES
复制标题
DOI：
10.1002/pol.1959.1203512807
复制
发表时间：
1959-01-01
影响因子：
3.4
通讯作者：
SLICHTER, WP
中科院分区：
文献类型：
--
作者：
SLICHTER, WP
众所周知，在酰胺基团之间具有偶数个亚甲基的脂族聚酰胺在比具有奇数个亚甲基的脂族聚酰胺更高的温度下熔融。过去的晶体学研究试图将酰胺基团的堆积与熔点的变化联系起来，但这些研究几乎都是在室温下进行的。在本研究中，通过X射线衍射在宽温度范围内检查了一系列聚酰胺纤维。在偶数聚酰胺中，在室温下发生的三斜结构转变为更对称的结构，其中链呈现六方堆积。后一种堆积在室温下发生在奇数聚合物中。后者中的极性基团出现在垂直于链轴的层中。偶数聚酰胺中的极性基团层在室温下相对于链轴倾斜，并且在高温下保持倾斜，即使侧链堆积变得与该系列的较低熔点（奇数）成员相同。极性基团沿着链的间距随着温度的升高而减小，但偶数聚合物中的减小相对小于奇数聚合物中的减小，并且极性更大的聚合物中的减小小于链烷烃化合物中的减小。这些变化归因于晶粒中链段的扭转和旋转运动。质子磁共振研究证明了烃段运动的开始，并定性地比较了该系列异构体成员之间链运动的约束。关于熔化过程的一些影响进行了讨论。
It is well known that aliphatic polyamides with even numbers of methylene groups between amide groups melt at higher temperatures than those with odd numbers of methylene groups. Crystallographic studies in the past have sought to relate the packing of the amide groups to the variations in melting point, but these studies have been made almost exclusively at room temperature. In the present study, series of polyamide fibers were examined by x‐ray diffraction over a wide range of temperatures. In the even‐numbered polyamides, the triclinic structure occurring at room temperature shifts to a more symmetrical structure in which the chains assume hexagonal packing. This latter packing occurs in the odd‐numbered polymers at room temperature. The polar groups in the latter occur in layers which are normal to the chain axes. The layers of polar groups in the even‐numbered polyamides are tilted with respect to the chain axes at room temperature, and remain tilted at high temperatures even though the lateral chain packing becomes the same as the lower‐melting (odd‐numbered) members of the series. The spacing between polar groups along the chain decreases with increasing temperature, but the decrease is relatively less in the even‐numbered than in the odd‐numbered polymers, and is less in the more polar than in the more paraffinic compounds. These changes are ascribed to torsional and rotational motions of chain segments in the crystallites. Proton magnetic resonance studies demonstrate the onset of motion of the hydrocarbon segments and compare qualitatively the constraints to chain motion among isomeric members of the series. Some implications regarding the melting process are discussed.