The influence of the nature of the catalytic system on zirconocene-catalyzed polymerization of alkyl methacrylates

Three non-bridged dimethylzirconocene complexes; i.e., bis(η⁵-cyclopentadienyl)dimethylzirconium (1), bis(η⁵-tert-butyl-cyclopentadienyl)dimethylzirconium (2), bis(η⁵-indenyl)dimethylzirconium (3), and the chiral zirconocene rac-ethylenebis(η⁵-indenyl)dimethylzirconium (4) were synthesized and used as catalysts for the polymerization of methyl methacrylate, MMA, combined with tris(pentafluorophenyl)borate (A) or tetrakis(pentafluorophenyl)borate dimethylanilinum salt (B) in the presence of ZnEt₂. The evolution of the polymerization characteristics; i.e., molecular weight, molecular-weight distribution, and yield were examined for the above systems. The influence of the nature of the solvent was also investigated. The aggregation behavior, the steric hindrance, and the lipophilicity of the active catalytic systems are the most important parameters determining the polymerization characteristics. The tacticity of the products is reported and the influence of the catalyst structure is discussed. Finally, the polymerization of other methacrylates (alkyl = butyl, hexyl, decyl, stearyl, and sec-butyl), was conducted and the effect of the nature of the alkyl ester group on the molecular and structural characteristics was established.