The development of new polymer structures driven by innovation in polymerization catalysis is key to disruptive advances in applied and fundamental polymer science. Expansion of the scope of structural possibilities in polymeric materials enhances the diversity in terms of architecture, composition, and stereochemistry that drives our knowledge of polymer physics, and properties available for new applications. In heterocyclic monomer systems, the driving force for incorporation of distinct monomers into a polymer chain is derived largely from an indiscriminate ring-strain which imparts significant versatility for the synthesis of new functional materials. Heterocyclic monomers can be polymerized via a variety of traditional ionic and catalytic approaches which each exhibit various advantages from a materials design perspective. In order to combine the advantages of a both an ionic and a catalytic approach, we looked to the historical Vandenberg catalyst as our ansatz for the development of new organoaluminum initiators. In this presentation, I will propose a structure and mechanism of polymerization for the Vandenberg catalyst, and present the synthesis of new initiators that contain key structural elements of the proposed Vandenberg catalyst structure. While some features of the Vandenberg catalyst could be replicated (e.g., isoselectivity), and new capabilities could be introduced (e.g., control of molecular weight and end-group functionality), the performance in terms of polymerization rate could not be improved upon using our defined molecular catalysts. Serendipity then led to the identification of a new class of polymerization initiators that operate via a distinct mechanism that is characteristically anionic in nature, provides control over molecular weight, chain-end functionality, and proceeds at a similar polymerization rate as the Vandenberg catalyst: The bis-(alkane-aluminum)-N-alkoxides, or BANANAs.

Design and synthesis of new initiators for the ring opening polymerization of epoxides inspired by the Vandenberg catalyst

253rd National Meeting (2017)

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