(654b) N-Al Lewis Pair Catalysts for Functional-Group Tolerant Living Epoxide Polymerization

Poly(ether)s derived from epoxides represent a versatile class of functional polymeric materials. Epoxide ring-strain depends little on monomer structure. This fact enables compositional control of structure-property relationships in this versatile macromolecular platform. Our lab has developed a class of stable, crystalline monoµ-alkoxo)bis(dialuminum) (MOB) initiators that offer the control of anionic ring opening polymerization, but with enhanced tolerance to chemical functionality and access to high molecular weight. The MOBs can be synthesized in a single step with purification afforded by direct crystallization from the reaction medium. The MOB-initiated living polymerizations create heterobifunctional materials at controlled molecular weights and with low dispersities. In more detailed mechanistic investigation, we found that during early stages of the polymerization that MOB initiators dimerize and rearrange. Significantly, an aluminum alkoxide site provided a location for monomer addition whereas a distinct N-Al adduct served as the catalyst. These two moieties were decoupled into distinct molecular species, and their reactivity was further explored separately. This enabled orthogonal control over polymer structure and polymerization rate. In this presentation, the synthesis, mechanism, and versatility of N-Al catalyst chemistry will be presented within the context of polyether-based materials design and synthesis.