Cp2Zr(13CH3)2 (1) has been used as a probe for the reactivity of metallocene−methylaluminoxane catalysts for olefin polymerization. A 1H and 13C NMR study of the reaction equilibria between Cp2Zr(13CH3)2 and Lewis acids such as AlMe3 (2), B(C6F5)3 (3), and methylaluminoxane (MAO) (4) has been performed. AlMe3 is always present in MAO solutions, and B(C6F5)3 is a relatively strong Lewis acid, which has a capacity to form and stabilize ion pairs comparable to that of MAO. The use of isotopically 13C-enriched dimethylzirconocene has permitted the study of these systems by 13C NMR in conditions as close as possible to usual polymerization conditions, which require large excesses of MAO for reaching high activities. The comparisons of the reactivity of Cp2Zr(13CH3)2 with B(C6F5)3 and with MAO have provided the first direct evidence of the formation in solution of monomeric [Cp2Zr(13CH3)]+[Me·MAO]- (8), of dimeric [Cp2Zr(13CH3)]2(μ-13CH3)+[Me·MAO]- (7), and of the [(Cp2Zr(μ-Me)2AlMe2]+[Me·MAO]- (9) cationic species, having MeMAO- counterions. The influence of temperature, Al/Zr mole ratio, and zirconium concentration on the equilibria of ion pair formation has been elucidated.

In concentrated suspensions, stratification occurs in experiments only for the higher size ratio α = 7. Simulations using a high Péclet number, additionally find stratification with α = 2, when ϕ is high enough. Our results provide a quantitative understanding of the conditions under which stratified colloidal films assemble. Our research has relevance for the design of coatings with targeted optical and mechanical properties at their surface.

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