Structural Investigation of Methylalumoxane Using Transmission Electron Microscopy
Structural Investigation of Methylalumoxane Using Transmission Electron Microscopy
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DOI：
10.1021/acs.macromol.5b00803
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发表时间：
2015-07
期刊：
影响因子：
5.5
通讯作者：
Harmen S. Zijlstra;M. Stuart;S. Harder
中科院分区：
文献类型：
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作者：
Harmen S. Zijlstra;M. Stuart;S. Harder
甲基铝氧烷（MAO）最初被发现并作为单中心催化剂的有效活化剂应用了几十年，但它仍然是一种神秘且知之甚少的化合物。使用一个适应的低温TEM设置，第一次干燥的MAO解决方案的图像已经获得。颗粒分析，尺寸比较，和分解研究产生的洞察所观察到的大MAO颗粒的结构性质，并可以关联回不同的MAO集群和它们的行为。所研究的微弧氧化样品被发现由高度聚集的分形与初级粒子的半径范围从100至60 nm时，增加样品年龄。这些发现支持了一个共同的颗粒烧结生长机制，其中初级颗粒聚集在一起，形成更大的二次颗粒。重复这一过程可以解释MAO的结构、平均分子量和活性随时间的急剧变化。
Decades after its initial discovery and application as a potent activator for single-site catalysts, methylalumoxane (MAO) still remains a mysterious and poorly understood compound. Using an adapted cryo-TEM setup, for the first time images of dried MAO solutions have been obtained. Particle analysis, size comparison, and decomposition studies yield insights into the structural nature of the observed large MAO particles and can be correlated back to different MAO clusters and their behavior. The studied MAO samples were found to consist of highly aggregated fractals with the radius of the primary particles ranging from ∼10 to 60 nm upon increasing sample age. These findings support a common particle sintering growing mechanism in which primary particles cluster together to form larger secondary particles. A repetition of this process could explain the dramatic change in structure, average molecular weight, and activity of MAO over time.