| Abstract
| - The synthesis and molecular structure of the first examples of monomeric lithium esterenolaluminates that serve as structural models for single-site anionic propagating centers, as well as themechanism of their polymerization of methacrylates catalyzed by conjugate organoaluminum Lewis acids,are reported. Reactions of isopropyl α-lithioisobutyrate (2) with suitable deaggregating and stabilizingorganoaluminum compounds such as MeAl(BHT)2 (BHT = 2,6-di-tert-butyl-4-methylphenolate) in hydrocarbons cleanly generate lithium ester enolaluminate complexes such as Li+[Me2CC(OiPr)OAlMe(BHT)2]-(3). Remarkably, complex 3 is isolable and exists as a monomer in both solid and solution states. Unlikethe uncontrolled polymerization of methacrylates by the aggregating enolate 2, the methacrylatepolymerization by the monomeric 3 is controlled but exhibits low activity. However, the well controlled andhighly active polymerization can be achieved by using the 3/MeAl(BHT)2 propagator/catalyst pair, which isconveniently generated by in situ mixing of 2 with 2 equiv of MeAl(BHT)2. The structure of the addedorganoaluminum compounds has marked effects on the degree of monomer activation, enolaluminateformation and reactivity, and polymerization control. Kinetics of the polymerization by the 3/MeAl(BHT)2pair suggest a bimolecular, activated-monomer anionic polymerization mechanism via single-site esterenolaluminate propagating centers. The molecular structures of activated monomer 1, aggregated initiator2, and monomeric propagator 3 have been determined by X-ray diffraction studies.
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