Crystalline structure changes in preoriented metallocene-based isotactic polypropylene upon annealing.
Crystalline structure changes in preoriented metallocene-based isotactic polypropylene upon annealing.
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DOI：
10.1021/jp400847p
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发表时间：
2013-06
期刊：
影响因子：
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通讯作者：
Yan Wang;Jia‐Zhuang Xu;Yanhui Chen;Kai Qiao;Ling Xu;X. Ji;Zhong‐Ming Li;B. Hsiao
中科院分区：
文献类型：
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作者：
Yan Wang;Jia‐Zhuang Xu;Yanhui Chen;Kai Qiao;Ling Xu;X. Ji;Zhong‐Ming Li;B. Hsiao
将预取向程度高、呈羊肉串状的部分熔融的茂金属基等规聚丙烯（m-iPP）在不同温度下退火，在130℃下等温结晶。采用同步加速器广角x射线衍射、小角x射线散射和差示扫描量热法研究了熔融和结晶过程。在较低温度下退火的m-iPP样品出现了片层增厚、横向生长和γ-晶体分数降低的现象。由于在有限的可结晶熔体体积内，α-和γ-晶体平行生长，导致γ-晶体的比例很低。此外，熔体中的拓扑约束决定了结晶演化中的链通量；这些链被增厚的薄片和横向生长消耗，在单晶胞内形成平行链的α-晶体。在中等退火温度下等温退火的m-iPP样品，可结晶熔体数量的增加导致γ-晶分数的增加。最终样品中存在高热稳定性的羊肉串（α-晶体）结构和新形成的宏观无取向结构。经过高温退火后，没有晶体存活，γ-晶体的形成非常有利；这归因于m-iPP分子的性质及其在130°C下的动态行为。由于缺乏取向核，形成了随机取向的片层。在不同尺度下结构协同变化的基础上，提出了不同退火温度下的形貌特征。
Partially melted metallocene-based isotactic polypropylene (m-iPP), which was preoriented with a high degree of molecular orientation and a shish-kebab structure, was annealed at various temperatures and isothermally crystallized at 130 °C. The melting and crystallization process was examined using synchrotron wide-angle X-ray diffraction, small-angle X-ray scattering, and differential scanning calorimetry. For the m-iPP samples annealed at relatively low temperatures, lamellar thickening, lateral growth, and a decrease in the γ-crystal fraction occurred. Because of parallel evolution of α- and γ-crystal growth in the limited crystallizable melt volume, the fraction of γ-crystals was very low. Furthermore, topological constraints in the melt dominate the chain flux in crystal evolution; the chains are consumed by the thickening lamellae and lateral growth, forming α-crystals with parallel chains in the unit cell. For the m-iPP samples isothermally annealed at medium annealing temperatures, the increase in the amount of crystallizable melt caused the γ-crystal fraction to increase. A shish-kebab (α-crystals) structure with high thermal stability and a newly formed macro-unoriented structure coexisted in the final sample. After annealing at high temperatures, at which no crystals survived, γ-crystal formation was greatly favored; this was attributed to the nature of m-iPP molecules and their dynamic behavior at 130 °C. Because of the lack of oriented nuclei, randomly oriented lamellae were formed. On the basis of the structural cooperative changes at different scales, the morphological features at different annealing temperatures were proposed.