Fundamental organometallic chemistry of the olefin polymerization activator methylaluminoxane (MAO). – Aime-AO

Methylaluminoxane (MAO) is a pivotal activator in olefin polymerization processes, allowing for high catalytic activity when combined with metallocene precatalysts. This enables the industrial production of polyolefins with precise control over composition and mass distribution. However, despite its widespread use, MAO remains an ill-defined material, and its precise structure, activation mechanism, and interactions in catalytic systems are still under debate. This knowledge gap hinders further optimization and rational design of improved MAO-based activators.
The Aime-AO project aims to provide a molecular-level understanding of MAO and supported derivatives through a combination of (surface) organometallic chemistry, cutting-edge ultra-high-field solid-state NMR spectroscopy (²7Al MAS NMR), and DFT calculations, focusing on the aluminum centers within MAO. Preliminary results have already demonstrated the exciting potential of our approach, as the 27Al NMR signatures revealed unprecedented insights into MAO’s structure. This project will push the boundaries of MAO characterization by exploiting the extreme conditions required for ²7Al NMR acquisition, made possible only by the 28.2 T ultra-high-field spectrometer in Lille. The unique combination of ultra-high magnetic field, fast magic angle spinning (MAS) frequencies, and advanced pulse sequences allows access to previously unresolved structural details. This breakthrough approach will significantly advance our understanding of MAO and related systems. The goal of Aime-AO is thus to unravel the structure, reactivity, and role of MAO in metallocene-based polymerization, ultimately enabling the development of more efficient catalytic systems.
The project is structured around 3 scientific work packages (WP).
The first WP is about the investigation of MAO at molecular level. It focuses on understanding the fundamental structure and reactivity of MAO. The influence of various modifications through the reaction with various reagents (Lewis acids, halide salts, doping agents) on the activation properties of MAO will be explored via homogeneous olefin polymerization studies. Advanced spectroscopic techniques, including multi-nuclear NMR and isotopic labeling, will be used to identify reactive centers and probe catalytic activation mechanisms.
Work package 2 will extend the investigation to supported MAO as polymerization activators. It will focus on the interaction of MAO with solid supports (e.g. silica) to develop more efficient heterogeneous catalysts. The goal is to improve catalytic performances by rational modification of supported MAO, including post-treatment with Lewis/Brønsted acids, surface functionalization, and targeted functionalization methods. Key structural insights will be gained through solid-state NMR, EXAFS, XPS, EPR and STEM-EDX spectroscopies.
The final WP will be dedicated to the development of advanced NMR methods specifically for the characterization of MAO and its derivatives under extreme acquisition conditions. It will focus on the development of high-resolution NMR techniques under ultra-high field conditions (up to 28.2 T) and high sample spinning speed. The unprecedented sensitivity and resolution will enable the application of high-resolution ²7Al MAS NMR, heteronuclear correlation experiments, and ab initio calculations to refine MAO’s structural models. These findings will establish new methodological benchmarks for studying complex quadrupolar nuclei in challenging environments.
Aime-AO brings together three leading research teams specializing in organometallic chemistry, surface chemistry, polymerization catalysis, and solid-state NMR spectroscopy. The project is expected to deliver fundamental breakthroughs in MAO chemistry, leading to improved catalyst design for industrial polyolefin production. By integrating experimental and computational approaches, Aime-AO will pave the way for the rational optimization of MAO-based activation systems.