Monoclinic Crystallites in Ethylene Copolymers Detected by Solid-State NMR and X-ray Diffraction
Monoclinic Crystallites in Ethylene Copolymers Detected by Solid-State NMR and X-ray Diffraction
复制标题
通过固态核磁共振和 X 射线衍射检测乙烯共聚物中的单斜晶
DOI：
10.1021/ma030132n
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发表时间：
2003
期刊：
影响因子：
5.5
通讯作者：
E. Sirota
中科院分区：
文献类型：
--
作者：
Weiguo Hu;E. Sirota
通过固体核磁共振和X-射线衍射技术，发现高共聚单体含量和大侧基的乙烯共聚物中存在单斜晶。在共聚物中，单斜晶型可以在环境温度和压力下在静态条件下成核和生长。在结晶过程中，随着共聚单体含量和冷却速率的增加，单斜晶系：正交晶系的群体比增加。与斜方晶形式相比，单斜晶微晶具有较低的平均熔点和可能较小的厚度。有人提出，在乙烯共聚物和在变形的线性聚乙烯单斜晶体结构的形成有一个共同的机制：单斜核有利于结晶-无定形界面，这增加了重要性的核尺寸减小，在增加共聚单体含量或作为剪切或快速冷却的结果。
By solid-state NMR and X-ray diffraction techniques, monoclinic crystallites are found to exist in ethylene copolymers with high comonomer content and bulky side groups. In the copolymers, the monoclinic form can nucleate and grow under quiescent conditions, at ambient temperature and pressure. The monoclinic:orthorhombic population ratio increases with comonomer content and cooling rate during crystallization. Compared to the orthorhombic form, monoclinic crystallites have a lower average melting point and possibly a smaller thickness. It is proposed that the formations of the monoclinic crystalline structures in ethylene copolymers and in deformed linear polyethylene share a common mechanism: the monoclinic nuclei are favored by the crystalline−amorphous interface, which increases in importance as the nucleus size decreases at increasing comonomer content or as a result of shear or fast cooling.