Abstract

In order to explore the effect of molecular structure on the crystallization and polymorphic behavior of β-nucleated isotactic polypropylene (β-iPP), four commercial iPP samples with different average isotacticities, molecular weights and isotactic distributions were used. The relationship between the molecular structure characteristics and β-crystallization behavior were investigated by means of xylene solvent fractionation (XS), successive self-nucleation and annealing fractionation (SSA), carbon-13 nuclear magnetic resonance spectrometry (¹³C NMR), gel permeation chromatography (GPC), melt index (MI) and differential scanning calorimetry (DSC). Results of molecular structure characterization revealed that their isotacticity can be ranged as F401 > 5014L > F03G ≈ T38F, while the order of their isotactic distribution width is 5014L ≈ T38F > F401 ≈ F03G. Results of crystallization kinetics revealed that the molecular weight of the samples has little effect on their crystallization and polymorphic behavior. Meanwhile, crystallization activation energy E_c can be ranged as 5014L < F401 < F03G < T38F, indicating that when the molecular weight was above a certain degree, the isotacticity is the main factor affecting the crystallization ability of β-type iPP (β-iPP). The higher the isotacticity and the wider the distribution is, the stronger the β-crystallization ability is. Moreover, the β-crystallization ability of the samples is closely related to the isotacticity of the sample, which can be effectively controlled by tuning the fraction of high isotacticity with high molecular weight components.

中文翻译：

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分子结构对β-核全同立构聚丙烯非等温结晶行为的影响

摘要

为了探索分子结构对β-有核全同立构聚丙烯（β-iPP）的结晶和多晶型行为的影响，我们使用了四种平均等规度，分子量和等规分布不同的商业iPP样品。通过二甲苯溶剂分离（XS），连续自成核和退火分离（SSA），碳13核磁共振光谱法研究了分子结构特征与β结晶行为之间的关系（¹³C NMR），凝胶渗透色谱法（GPC），熔体指数（MI）和差示扫描量热法（DSC）。分子结构表征结果表明，它们的全同立构规整度范围为F401> 5014L> F03G≈T38F，而它们的全同立构分布宽度顺序为5014L≈T38F> F401≈F03G。结晶动力学结果表明，样品的分子量对其结晶和多晶型行为影响很小。同时，结晶活化能E _c分子量范围为5014L <F401 <F03G <T38F，表明当分子量超过一定程度时，全同立构规整度是影响β型iPP（β-iPP）结晶能力的主要因素。等规度越高，分布越宽，β结晶能力越强。此外，样品的β-结晶能力与样品的全同立构规整度密切相关，这可以通过调节具有高分子量组分的高全同立构规整度的分数来有效地控制。