Time-resolved X-ray scattering and calorimetric studies on the crystallization behaviors of poly(ethylene terephthalate) (PET) and its copolymers containing isophthalate units
Time-resolved X-ray scattering and calorimetric studies on the crystallization behaviors of poly(ethylene terephthalate) (PET) and its copolymers containing isophthalate units
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DOI：
10.1016/s0032-3861(03)00130-7
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发表时间：
2003-04-01
期刊：
影响因子：
4.6
通讯作者：
Ree, M
中科院分区：
文献类型：
--
作者：
Lee, B;Shin, TJ;Ree, M
对进行等温结晶的 PET 及其共聚物进行时间分辨小角 X 射线散射 (SAXS) 测量。还进行了广角 X 射线衍射和差示扫描量热测量。我们对 PET 和共聚物的 SAXS 结果的数据分析清楚地表明，单层厚度 l(1)（直接从测量的 SAXS 剖面的相关函数得出）是层状晶体厚度 d(c)，而不是非晶层厚度 d(a)。发现观察到的 d(c) 值总是小于 d(a)，无论聚合物组成如何。 d(c) 高度依赖于结晶温度，表明过冷程度是决定层状晶体厚度的主要因素。然而，等温结晶中不会发生增稠。发现共聚物中扭结的间苯二甲酸酯单元在结晶过程中大部分被排除在层状晶体之外，导致非晶层厚度增加。此外，发现间苯二甲酸酯单元的扭结、刚性性质限制了晶体沿共聚物链轴的生长，并且还降低了它们的结晶度。与 d(c) 不同，d(a) 随着结晶时间的增加而减小，导致层状堆叠中的长周期减少。本文通过考虑可能影响结晶行为的几个因素来解释 d(a) 的下降：层状堆叠中的 d(a) 分布及其随时间的变化、层状堆叠中的层晶数量及其对 SAXS 剖面的影响，以及非晶层中聚合物链的松弛。 (C) 2003 Elsevier Science Ltd. 保留所有权利。
Time-resolved small-angle X-ray scattering (SAXS) measurements were carried out for PET and its copolymers undergoing isothermal crystallization. Wide-angle X-ray diffraction and differential scanning calorimetric measurements were also performed. Our data analysis of the SAXS results for PET and the copolymers clearly demonstrate that the one layer thickness l(1) (derived directly from the correlation functions of the measured SAXS profiles) is the lamellar crystal thickness d(c), not the amorphous layer thickness d(a). The observed d(c) values are found to be always smaller than d(a), regardless of polymer composition. d(c) is highly dependent on the crystallization temperature, showing that the degree of supercooling is the major factor determining the thickness of lamellar crystals. No thickening, however, occurs in isothermal crystallizations. The kinked isophthalate units in the copolymer are found to be mostly excluded from the lamellar crystals during the crystallization process, leading to an increase of the amorphous layer thickness. Moreover, the kinked, rigid nature of the isophthalate unit was found to restrict crystal growth along the chain axis of the copolymers and also to lower their crystallinity. Unlike d(c), d(a) decreases with crystallization time, causing a reduction of the long period in the lamellar stack. This drop in d(a) is interpreted in this paper by taking into account several factors that could influence crystallization behavior: the d(a) distribution in the lamellar stacks and its variation with time, the number of lamellae in the lamellar stacks and their effect on the SAXS profile, and the relaxation of polymer chains in the amorphous layers. (C) 2003 Elsevier Science Ltd. All rights reserved.