New methods for characterization of methylaluminoxanes (MAO) and determination of trimethylaluminum (TMA) using proton NMR are reported. Addition of excess perdeuteriotetrahydrofuran to sharpen and shift the TMA peak followed by curve fitting to remove residual overlap between the TMA and MAO peaks allows accurate, precise, and rapid quantitation of TMA and MAO in solution. The analysis also provides determination of all the solution components of MAO preparations and the number of methyl groups per aluminum in MAO when combined with an independent determination of the aluminum content.

New methods for characterization of methylaluminoxanes (MAO) and determination of trimethylaluminum (TMA) using proton NMR are reported. Addition of excess perdeuterotetrahydrofuran to sharpen and shift the TMA followed by curve fitting to remove residual overlap between the TMA and MAO peaks allow accurate, precise and rapid quantitation of TMA and MAO in solution. The analysis also provides determination of all the solution components of MAO preparations and the number of methyl groups per aluminum in MAO when combined with an independent determination of the aluminum content. Accurate number average molecular weights for MAOs are determined from freezing point depression data corrected for TMA and other small molecule concentrations obtained using the NMR method.Methylaluminoxane (MAO) is an important co-catalyst for the oligomerization and polymerization of a variety of monomers. (1-7) Despite the commercial importance of MAO and the considerable effort directed at its characterization, the structure of MAO remains unclear. (7-10) The presence of multiple equilibria and alkyl group exchange prevent easy direct structural characterization. Methylaluminoxane is usually written as the oligomer formula [-Al(CH 3 )0-] n and the literature contains many postulated structures, including chains, cages, and rings of various sorts. (7-10) Further, residual trimethylaluminum (TMA) in MAO preparations clouds structural interpretations. (7-11)Controlled hydrolysis of TMA in toluene or other hydrocarbon solvent to form MAO leaves residual TMA in the product solution. (7,10,11) The TMA in MAO is present as free and bound species according to the equilibrium:(1) Commercial MAOs are known to contain significant quantities of TMA which can have important effects on the catalytic activity of the MAO. (10-11) The amount of residual TMA is an important parameter for characterizing MAO and for controlling MAO product quality.Several approaches to determine residual TMA have been explored in the Corresponding author.

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