Morphology Investigation of Stereoblock Polypropylene Elastomer
Morphology Investigation of Stereoblock Polypropylene Elastomer
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DOI：
10.1021/ma9915531
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发表时间：
2000
期刊：
影响因子：
5.5
通讯作者：
R. Kravchenko;B. Sauer;R. S. Mclean;M. Keating;A. Cotts;Young Ha Kim
中科院分区：
文献类型：
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作者：
R. Kravchenko;B. Sauer;R. S. Mclean;M. Keating;A. Cotts;Young Ha Kim
半结晶聚丙烯（PP）是一类重要的热塑性弹性体，它同时含有有规立构的全同立构和无规立构。该聚合物中的全同立构链段可以结晶形成物理交联，而无规立构链段作为连续的无定形相。1，2已经开发了多种合成方法用于使用非均相齐格勒-纳塔（ZN）1-4和均相双烯烃5 -8催化剂制备该材料。用非均相催化剂生产的聚合物往往具有宽的分子量和立构规整度分布，而用均相桥连双烯烃生产的聚合物则均匀得多。6，9由非桥连的双（2-芳基茚基）环己烯衍生的弹性聚丙烯7，10是其他两种类型之间的中间体：它们可以被分离成不同立构规整度和结晶度的几个部分，11-13，但与用非均相ZN催化剂生产的聚合物相反，3，4这些部分的分子量变化不大。提出的“振荡”机制的立体嵌段形成与双（2-芳基茚基）环己烯涉及催化剂异构化之间的isosspecific和asspecific构象在一个单一的聚合物链的生长过程中，导致全同立构和无规立构序列，分别。7聚合过程中至少两种类型的活性物质的存在可以解释所产生的聚合物的不均匀性。12通过差示扫描量热法（DSC）和光学去极化技术对用“振荡”催化剂产生的聚丙烯进行的研究表明，宽的熔融转变和快速和缓慢结晶状态的存在可能与不同长度的可结晶序列的共存有关。11、12然而，迄今为止还没有尝试过硬链段嵌段长度的实验测量。为了更好地了解来自双（2-芳基茚基）环己烯的弹性聚丙烯的域结构，我们已经研究了这些材料的结晶域的热性能和形态，使用热分馏DSC，原子力显微镜（AFM），硝酸消化结合凝胶渗透色谱法（GPC）分析。按照文献方法在23-25 ℃下在液体丙烯中用双（2-苯基茚基）二氯化锆/甲基铝氧烷作为催化剂进行聚合。14所得聚丙烯样品具有全同立构五单元组含量（% mmmm）25-30%（13 C NMR），15，16 Mw）240 000-260 000，和范围为2.7 - 4.4的分子量分布（通过NMR测定）。
Semicrystalline polypropylene (PP) containing both stereoregular isotactic and random atactic sequences belongs to an important class of thermoplastic elastomers. The isotactic segments in this polymer can crystallize forming physical cross-links while the atactic segments serve as a continuous amorphous phase. 1, 2 Various synthetic methods have been developed for the preparation of this material using both heterogeneous Ziegler-Natta (ZN) 1-4 and homogeneous metallocene5-8 catalysts. Polymers produced with heterogeneous catalysts tend to have broad molecular weight and tacticity distributions, 3, 4 while those generated with homogeneous bridged metallocenes are much more uniform. 6, 9 Elastomeric polypropylenes derived from the unbridged bis (2-arylindenyl) metallocenes7, 10 are intermediate between the other two types: they can be separated into several fractions of different tacticity and crystallinity, 11-13 but in contrast to polymers produced with heterogeneous ZN catalysts, 3, 4 these fractions do not vary strongly in their molecular weight. The proposed “oscillating” mechanism for the stereoblock formation with bis (2-arylindenyl) metallocenes involves catalyst isomerization between an isospecific and an aspecific conformation during the growth of a single polymer chain resulting into isotactic and atactic sequences, respectively. 7 The presence of at least two types of active species during polymerization may account for the heterogeneity of produced polymers. 12 Studies of polypropylenes generated with the “oscillating” catalysts by differential scanning calorimetry (DSC) and optical depolarization techniques reveal broad melting transitions and the presence of fast and slow crystallization regimes possibly related to the coexistence of crystallizable sequences of different lengths. 11, 12 However, no experimental measurements of the hard segment block lengths have been attempted so far. To better understand the domain structure of elastomeric polypropylenes derived from bis (2-arylindenyl) metallocenes, we have investigated the thermal properties and morphology of the crystalline domains of these materials using thermal fractionation DSC, atomic force microscopy (AFM), and nitric acid digestion in combination with analysis by gel permeation chromatography (GPC). Polymerizations were conducted following a literature procedure at 23-25 C in liquid propylene with bis (2-phenylindenyl) zirconium dichloride/methylaluminoxane as catalyst. 14 The resulting polypropylene samples had isotactic pentad contents% mmmm) 25-30%(13C NMR), 15, 16 Mw) 240 000-260 000, and molecular weight distributions ranging from 2.7 to 4.4 (determined by