Several spectroscopic techniques have been applied in a concerted way to investigate the local structure and the function of the chromium sites in a series of Cr[CH(SiMe₃)₂]₃/SiO₂ catalysts for ethene polymerization differing in the chromium loading, and to correlate them with the microstructure of the produced polyethylene (PE). According to previous studies, the density of the produced PE is proportional to the Cr loading: the higher is the Cr loading, the lower is the PE density, because of an increase in the content of short-chain branching. Herein, the nature of the branches and their enchainment in the polymer has been further investigated to determine the different properties of the produced polymers, and the so detected differences have been traced back by spectroscopic analysis to the presence of two different types of Cr sites working in tandem: mono-grafted (≡SiO-)Cr[CH(SiMe₃)₂]₂ species that are responsible for ethene oligomerization, and bis-grafted (≡SiO-)₂CrCH(SiMe₃)₂ species that account for ethene homo- and co-polymerization. The relative abundance of the two species depends on the chromium loading. Moreover, we have also found that carbon monoxide selectively poisons the sites responsible for ethene oligomerization, indicating a possible strategy for the fine regulation of the properties of the produced PE.

协同使用了几种光谱技术研究了一系列Cr [CH（SiMe ₃）₂ ] ₃ / SiO _2中铬的局部结构和铬位点的功能。乙烯聚合用催化剂的铬负载量不同，并将它们与生产的聚乙烯（PE）的微观结构相关联。根据先前的研究，所产生的PE的密度与Cr的含量成正比：Cr的含量越高，PE的密度就越低，这是因为短链支链含量的增加。在此，进一步研究了聚合物中支链的性质和它们的键合，以确定所生产的聚合物的不同性质，如此检测到的差异已通过光谱分析追溯到存在两种不同类型的Cr位点串联：单接枝（≡SiO-）Cr [CH（SiMe ₃）₂ ] ₂乙烯低聚反应的有机物种，以及乙烯均聚和共聚的双接枝（≡SiO-）₂ CrCH（SiMe ₃）₂物种。这两种物质的相对丰度取决于铬的负载量。此外，我们还发现一氧化碳选择性地中毒了负责乙烯低聚的位点，这表明了对所生产的聚乙烯的性能进行精细调节的可能策略。