Structure-property correlations in polypropylene from metallocene catalysts: Stereodefective, regioregular isotactic polypropylene
Structure-property correlations in polypropylene from metallocene catalysts: Stereodefective, regioregular isotactic polypropylene
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DOI：
10.1021/ja045684f
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发表时间：
2004-12-29
影响因子：
15
通讯作者：
Laishevtsev, IP
中科院分区：
文献类型：
--
作者：
De Rosa, C;Auriemma, F;Laishevtsev, IP
一系列基于MAO活化的Cl-对称茚基-柄型-二噻吩并环戊二烯基的α-conocene已用于制备中等至高分子量、具有不同立构规整度且无区域误差的全同立构聚丙烯。分析了rr缺陷的存在对聚丙烯多晶型行为和力学性能的影响。rr缺陷的存在诱导γ形式的结晶和α和γ形式之间的无序修饰的中间体。γ型缺陷的数量与全同立构序列的平均长度之间存在线性关系，当γ型缺陷的浓度较低时（最高可达3- 4%），样品的熔融温度较高（160-130 ℃），表现为硬塑性材料;具有较高rr含量（在4-6%范围内）和约115-120 ℃熔融温度的样品是高度柔性的热塑性材料，并且，最后，具有在7-11%范围内的rr缺陷浓度和在8-110 ℃范围内的熔融温度的样品是具有高强度的热塑性弹性体。通过新茂金属催化剂的定制设计实现的链微结构的微调已经允许生产具有所需性能的新聚丙烯，其介于刚性塑料和弹性体材料的性能之间。
A series of MAO-activated Cl-symmetric indenyl-ansa-dithienocyclopentadienyl-based zir-conocenes have been used to produce isotactic polypropylenes of medium to high molecular weights, of different degrees of stereoregularity, and free from regioerrors. The effect of the presence of rr defects on the polymorphic behavior and mechanical properties of polypropylene is analyzed. The presence of rr defects induces crystallization of gamma form and of disordered modifications intermediate between alpha and gamma forms. A linear relationship between the amount of gamma form and the average length of isotactic sequences has been found. Samples with low concentration of rr defects, up to 3-4%, present high melting temperatures, in the range 160-130 degreesC, and behave as stiff-plastic materials; sample with higher rr content, in the range 4-6% and melting temperatures around 115-120 degreesC are highly flexible thermoplastic materials, and, finally, samples with concentration of rr defects in the range 7-11% and melting temperatures in the range 8-110 degreesC are thermoplastic elastomers with high strength. The fine-tuning of the chain microstructure, achieved by a tailored design of new metallocene catalysts, has allowed production of new polypropylenes having desired properties, intermediate between those of stiff plastic and elastomeric materials.