Real-Time Analysis of Methylalumoxane Formation

20 August 2020, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

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’ve 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 energy than any previously calculated.

Keywords

activator
hydrolysis
methylalumoxane
electrospray ionization mass spectrometry
real-time analysis

Supplementary materials

Title
Description
Actions
Title
Manuscript chemrxiv 200818 HZ CC ML EL AJ SM
Description
Actions
Title
SI chemrxiv 200819 SM2 AJ2
Description
Actions

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.