茂金属
甲基铝氧烷
阳离子聚合
催化作用
后茂金属催化剂
聚合
烯烃纤维
化学
高分子化学
烯烃聚合
光化学
材料科学
有机化学
聚合物
作者
Marjolein E. Z. Velthoen,Jelle M. Boereboom,Rosa E. Bulo,Bert M. Weckhuysen
标识
DOI:10.1016/j.cattod.2018.11.019
摘要
Metallocene-based olefin polymerization catalysts often require large excesses of co-catalyst for optimal catalyst activation. In this work, mechanistic insights into the activation of supported metallocenes by methylaluminoxane as co-catalyst are acquired. UV–vis diffuse reflectance (DR) spectroscopy of five metallocene catalysts with varying co-catalyst loading reveals the presence of different metallocene species on the surface of the catalyst particles. Deconvolution of the obtained spectra, in combination with an extensive TD–DFT study of UV–vis DR spectra of metallocene structures results in a proposed activation mechanism. We find that with increasing MAO loading, more AlMe2+-bound metallocenes are observed with a shift towards the trimethylaluminum-stabilized cationic methylated metallocene compound. This shift can be directly correlated with a higher activity in the olefin polymerization reaction. Based on this finding, we propose a universal metallocene activation mechanism in which the cationic methylated metallocene is the active species. This species is formed through initial interaction with AlMe2+, followed by ligand exchange with MAO and stabilized in complex with trimethylaluminum as a dormant species.
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