Molecular Weight Dependency of Surface Free Energy of Native and Stabilized Crystallites in Isotactic Polypropylene
Molecular Weight Dependency of Surface Free Energy of Native and Stabilized Crystallites in Isotactic Polypropylene
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等规聚丙烯中天然和稳定微晶表面自由能的分子量依赖性
DOI：
10.1021/mz500599r
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发表时间：
2014-11-01
影响因子：
7.015
通讯作者：
Men, Yongfeng
中科院分区：
文献类型：
--
作者：
Lu, Ying;Wang, Yaotao;Men, Yongfeng
采用变温小角X射线散射技术研究了两种等规聚丙烯样品的结晶熔融行为，研究了分子量对结晶熔融行为的影响。在片层厚度与温度成反比的相图中，在无限片层厚度下，晶化和熔化行为可以用不同斜率和不同极限温度的两个线性关系来描述。结晶线的斜率取决于刚形成的原生微晶的表面自由能，而熔化线的斜率与稳定微晶的表面自由能有关。两个聚丙烯样品显示出不同的结晶线和熔融线，表明强烈的变化，在本地以及稳定的微晶的表面自由能。这种变化是不同分子量样品结晶过程中分子构象变化的结果。事实上，低分子量样品广泛地结晶成延伸链构象，而高分子量样品最终以正常的折叠链微晶结束。
Two isotactic polypropylene samples were investigated to study the influence of molecular weight on the crystallization and meting behaviors via temperature- dependent small-angle X-ray scattering techniques. In a phase diagram of inverse lamellar thickness and temperature, the crystallization and melting behaviors can be described by two linear dependencies of different slopes and different limiting temperatures at infinite crystalline lamellar thickness. The slope of the crystallization line depends on the surface free energy of the just formed native crystallites, whereas that of the melting line is linked to the surface free energy of stabilized ones. The two polypropylene samples showed different crystallization lines and melting lines, indicating strong changes in surface free energies of the native as well as stabilized crystallites. Such changes are consequences of changes in molecular conformation during crystallization for samples with different molecular weights. Indeed, the low molecular weight sample crystallizes extensively into an extended-chain conformation whereas the high molecular weight one ends up with normal folded-chain crystallites.