AI Article Synopsis
- The study examines how the anions from methylalumoxane (MAO) can be analyzed using mass spectrometry to understand the changes occurring during oxidation.
- It reveals that while immediate oxidation of MAO leads to gelation, the composition of the main oligomeric anions remains unchanged at first.
- Over time, the reaction incorporates methylaluminum methoxide (Me AlOMe) into the anions, confirming the formation of oxidized MAO oligomers, which also allows for tracking the MAO's environmental history.
Article Abstract
The anions formed from methylalumoxane (MAO) and suitable donors (e.g. octamethyltrisiloxane) are amenable to mass spectrometric (MS) analysis. Their composition as deduced from this data allows direct insight into the chemical transformations of their neutral precursors. One such process is oxidation, which is well-known to be facile for MAO without any clear idea of what actually occurs at a molecular level. Addition of O to MAO results in immediate gelation, but MS analysis reveals no corresponding change to the composition of the principal oligomeric anions. A slow (hours) reaction does occur that involves net incorporation of Me AlOMe into the oligomeric anions, and the identities of the OMe-containing anions were confirmed by H NMR spectroscopy, MS/MS analysis, and addition of an authentic sample of Me AlOMe to MAO. The result tallies with the fact that addition of O to MAO produces Me AlOMe from free Me Al which eventually leads to formation of oxidized MAO oligomers and changes in ion abundance. Aging of the oxygenated MAO results in further growth of the oligomers similar to that of the non-oxidized species. Mass spectrometric analysis therefore reveals useful insights into the environmental history of a given MAO batch.
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| http://dx.doi.org/10.1002/chem.201705458 | DOI Listing |
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