Single-Site, Organometallic Aluminum Catalysts for the Precise Group Transfer Polymerization of Michael-Type Monomers

Unlike different types of Lewis pairs as polymerization catalysts for acrylic monomers, organometallic aluminum(III) compounds are reported that show a surprisingly high polymerization activity even without an additional Lewis base. DFT calculations, end group analysis and kinetic investigations clearly suggest a main group element (MGE) group transfer polymerization (GTP) mechanism analogous to the known metal-mediated GTP mechanism. The novel catalysts perform a precision polymerization of a broad variety of monomers, ranging from 2-isopropenyl-2-oxazoline to tert-butylmethacrylate and N,N-dimethylacrylamide. Additionally, extended Michael-type structures like 4-vinyl pyridine are accessible. Especially the Al(III) half-metallocenes show an almost quantitative initiator efficiency, and, combined with the living character of the polymerization reactions, they enable the synthesis of block copolymers, even with unconventional monomers like vinyl phosphonates.