Behaviour of differently produced methylalumoxanes in the phase separation with diethyl ether and molecular weight estimations

Abstract

Abstract:Cryoscopic molecular weight estimations and phase separation experiments of differently produced methylalumoxanes showed diverse behaviour. The cryoscopic molecular weight estimations showed higher molecular weights caused by increasing methyl conversion. The average molecular weight in benzene lay between 1000 t o 2000 while the solvent 1.4-dioxane delivered smaller molecular weights ( factor 2 t o 4 1. Molecular weights in trimethylaluminium were similar t o those in benzene. In phase separation experiments we obtained an increasing volume portion of lower phase with increasing methyl conversion during production. There was a decisive influence of circulation circumstances a t the ice surface and the trimethylaluminium concentration at production according to the behaviour in phase separation experiments.

A Density Functional Theory (DFT) Quantum-Chemical Approach to the Real Structure of Poly(methylaluminoxane)

“…As data in Table 3 show, the formation of "true" MAO is an exothermic reaction if n = 6, 9 and 12, but endothermic if n = 15. These results are consistent with experimental data [33] which prove the molecular weight of "true" MAO to be f1 100-1 200. As has been suggested by Sinn et al, [21] "if two Al1(CH 3 ) 2 -groups of two different molecules of "true"-MAO react with each other splitting off one TMA molecule, a big molecule MAO is produced with a molecular weight of M -A 1 200".…”

“…According to Lacroix et al, [33] Figure 7. Sinn et al [17] consider that the basic structure of MAO has the composition Al 12 [21] We carried out DFT calculations of the energetic stability of these molecular models [21] (Figure 9, structures A and B) for comparison with the model suggested in the present work ( Figure 8, structure C).…”

Methylalumoxane – History, Production, Properties, and Applications

“…As mentioned before, the variable Me‐to‐Al ratio in MAO depends on the manner in which MAO is produced. Sinn and co‐workers studied these ratios by using both individually synthesized and commercially obtained samples of MAO 37. After removal of unbound Me 3 Al, they reported Me/Al ratios ranging from 1.48 to 1.62.…”

“…Molecular weight ( M w ) estimates for MAO range from 700–20000 g/mol, which implies clusters containing 12–200 Al atoms 37,46. These values might vary depending on whether the M w for regular MAO or that for the MAO anion is estimated 49,50.…”

Diffusion of Methylaluminoxane (MAO) in Toluene Probed by1H NMR Spin-Lattice Relaxation Time

“…A molecular weight range from 1 500 to 3 000 g N mol -1 is obtained, which is higher than the molecular weight range of 700 to 1 200 g N mol -1 obtained by cryoscopic measurements of MAO dissolved in benzene. [19] When keeping in mind all the approximations used when deriving the molecular weight range in our study, it is a reasonable fit to the concentration-dependent diffusivity of MAO.…”