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Issue 2, 2021
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Real-time analysis of methylalumoxane formation

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Abstract

Methylalumoxane (MAO), a perennially useful activator for olefin polymerization precatalysts, is famously intractable to structural elucidation, consisting as it does of a complex mixture of oligomers generated from hydrolysis of pyrophoric trimethylaluminum (TMA). Electrospray ionization mass spectrometry (ESI-MS) is capable of studying those oligomers that become charged during the activation process. We have exploited that ability to probe the synthesis of MAO in real time, starting less than a minute after the mixing of H2O and TMA and tracking the first half hour of reactivity. We find that the process does not involve an incremental build-up of oligomers; instead, oligomerization to species containing 12–15 aluminum atoms happens within a minute, with slower aggregation to higher molecular weight ions. The principal activated product of the benchtop synthesis is the same as that observed in industrial samples, namely [(MeAlO)16(Me3Al)6Me], and we have computationally located a new sheet structure for this ion 94 kJ mol−1 lower in Gibbs free energy than any previously calculated.

Graphical abstract: Real-time analysis of methylalumoxane formation

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Supplementary files

Article information


Submitted
14 Sep 2020
Accepted
23 Oct 2020
First published
27 Oct 2020

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2021,12, 546-551
Article type
Edge Article

Real-time analysis of methylalumoxane formation

A. Joshi, H. S. Zijlstra, E. Liles, C. Concepcion, M. Linnolahti and J. S. McIndoe, Chem. Sci., 2021, 12, 546
DOI: 10.1039/D0SC05075J

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