In an earlier, unpublished study, we obtained ESI-MS and 1 H NMR spectra of a commercial and proprietary sample of h-MAO with nearly identical Al (13. If one recognizes that the proprietary sample has an initial composition (average m/z = 1709 Da) that is similar to the commercial sample at three weeks (average m/z = 1710 Da), the slower rate of aging of the former can be rationalized as being further located along the same growth curve (dashed line in Figure ). Presumably the onset of gelation is also dependent on 𝑀 ̅ 𝑤 51 of the material present and thus more rapid in the material with higher m/z anions. NMR experiments in THF-d8 demonstrate that the proprietary formulation with higher m/z anions has ca. 50% higher activator content based on the intensity of signals due to the [Me2Al(THF)2] + cation. This difference is maintained for the aged samples, as both the sol and gel phases are soluble in excess THF or sufficient amounts of OMTS (ca. 2 mol% in PhF). The only time dependent change seen is the total Me3Al content (and total Al content) which decreases slightly in both samples, presumably due to volatiles evaporating from screw-top vials inside the glovebox over the three-week period of these experiments.